CHAPTER IV

THE CAUSAL THEORY OF PERCEPTION

    At every step in the preceding chapters we have been brought against the causal theory of perception. We saw too that it tended to land common-sense in conclusions that it did not want. Common- sense started with naïf realism and only left it when and inasmuch as it was forced to do so. But it was forced away from it at certain points by arguments independent of the causal theory of perception, and, whenever this happened, it introduced the causal view. For no sooner had common-sense distinguished between appearance and reality than it was forced to give some account of the relations between them in those objects which it perceived as being all of a piece, and, but for difficulties, would have continued to regard as all equally real. Unhesitatingly and without reflexion it rushed to the causal theory. The reality caused the perception of the appearances, and from the appearances you could get information about the reality. But the theory, whether true or not, was a bad ally for common- sense realism. It was not content to act as a humble account of the connexion of those two aspects which common-sense had been forced to separate. It could not leave common-sense with that amount of naïf realism that it wanted and that other arguments allowed to it. For the causal view itself becomes the strongest argument against naïf realism, and, when pursued, seems to leave it no foothold in the world. Educated common-sense followed it in its rejection of secondary qualities, but refused to give up primaries and so matters stand to-day with science --except when it becomes phenomenalistic. But it was impossible for the philosopher to stop there; he was hurried on to the Thing-in-itself, and, in its mysterious presence, according to temperament he worshipped with Mr Spencer, constructed moral fairy tales with Kant, or began to ask, as we propose to do, whether his leader -- the causal theory -- which he had so innocently followed might not be a will o' the wisp.

    We propose to discuss in the present chapter the arguments against naïf realism that depend on causation. We shall have to enquire where precisely they will let us rest and what precisely is meant by the view which is certainly held vaguely by educated common-sense that our perceptions have causes and that some relation is to be found between the nature of these causes and the reality of the objects perceived.

    The essential argument that we have to examine is that from the relativity of objects of perception to an organ; but we shall find that the causal theory once introduced exerts an influence on all the other arguments which we have previously discussed without assuming it.

    It seems to be held that relativity to an organ is fatal to the reality of sense qualities. The statement to begin with is vague, but at the very outset we must carefully distinguish it from the position that I discussed in the last chapter which held that, since one of the qualities which reflexion shows to belong to every object that we perceive is that of standing in the relation of being perceived, there can be no ground for supposing that any object that can be perceived ever exists out of that relation. The argument here to be discussed introduces indeed a relation; but it is a relation to the body and not to the mind. Let me quote Bradley as an exponent of the argument under discussion. 'A thing is coloured, but, except to some eye, it seems not coloured at all. And the eye . . . relation to which appears somehow to make the quality -- does that itself possess colour? Clearly not unless there be another eye that sees it. Nothing therefore is really coloured; colour seems only to belong to what is itself colourless. And the same result holds with heat and cold¹.

    There is clearly an analogy between this argument and the one for pure phenomenalism. It says: No doubt when you perceive red you do not at the same time perceive a relation to your eye. Still, in considering whether red be real or only an appearance, you ought clearly to take into account all that you can possibly find out about it. Now one of the things that you can find out about it is that it is never perceived except when it is also possible to find that it stands in certain relations to your eye. What right then have you to believe that it can exist out of those relations? The argument is then confused with the formally similar one for phenomenalism, because the relation mentioned in it is confused with that of being perceived, which plays the same part in that argument. It is, however, easy to see that the two relations cannot be identical, since relativity to an organ cannot possibly be the same as relativity to a percipient mind.

    Our first duty then will be to clear up the relations between the two arguments. Call the present one b and the phenomenalistic one a. In the first place b is no ground by itself for believing the phenomenalistic conclusion. The fact that whatever I perceive has a certain relation to an organ of perception cannot possibly be by itself any reason for supposing that it does not exist when it is not perceived. For the relation to the organ, whatever it may be, is not the relation of being perceived, since that is a relation to the mind and not to the body. Hence, although b might prove, e.g. that there is no reason to suppose that red ever exists out of some relation to the eye, yet, as this relation cannot itself be that of being perceived, there can be no reason supplied by b alone that red does not exist in this relation R to the eye even when it is not perceived. It is clear that to prove the phenomenalistic conclusion we need something more than b, viz. a premise to the effect that the relation R to the organ of sense, whatever it may be, implies also the relation of being perceived. Without this we merely know that we never do perceive X without being able to show that it is also related to some organ; and this leaves two alternatives open to us beside phenomenalism, viz.

1. that the object continues to exist in the same relation to our organs even when we cease to perceive it, or
2. that, whilst it cannot be perceived when it ceases to stand in this relation to the organ, yet it does not cease to exist when it ceases to stand in this relation.

And, as before, the sole reason so far for choosing phenomenalism rather than one of these alternatives is the old argument a which we have already discussed.

    So far I have taken the relativity argument quite generally, and have shown that, unless the relation R to an organ which it claims to discover can be proved to imply the relation P of being perceived, it has no bearing on phenomenalism whatever. We will now consider R a little more closely and see if there be any reason to suppose that it implies P. What is the nature of R? It is clear that at this stage we must not tie ourselves down to the causal theory which common-sense commonly assumes as the connecting link between appearance and reality when it thinks it has discovered a distinction between the two. For the perceived relation is supposed to connect our organs of perception with what we perceive and the argument from it is supposed to show that what we perceive is always an appearance. On the other hand the causal relation is supposed to connect our perception of a given object taken as a mental event with the supposed real cause of that perception which is not itself the object of it. Another point to notice about R is that it must be a relation of whose existence and nature we must be able to learn, and we must therefore be careful that we do not, by assuming that the presence of R makes the objects of our perception appearances, assume that R itself is at once an object of a perception and a reality.

    It is tolerably easy to see by considering particular cases what sort of a relation R must be. We shall see that it is not supposed to be a perceptible relation, and that is as it should be. Let us consider sight for example. I see a coloured object. I shut my eye or am deprived of it by accident and I no longer see such an object. So too if I turn my eye away and replace it by my ear. Again my eye is a very complicated organ in which various distinct parts can be found, and, by lesions of the eye and the comparison of it with other optical instruments I can discover approximately what role each part plays in the act of vision. We can find reason for supposing that the rods and cones are connected with colour vision, and convergence and accommodation with the perception of distance. The relation R then splits up into several distinct ones in the case of sight.

1. Without eyes or with them shut I can see nothing.
2. Some at least of the distinguishable characteristics in the object perceived cannot be perceived in the absence of certain appropriate structures in the eye.
3. With open eyes possessing all the appropriate parts in working order what I perceive depends on the position of my body.

To put the matter more generally we must say:

1. Without special organs you cannot perceive the special qualities like sound, colour, extension, etc.
2. With such organs there is reason to believe that some of the special characteristics of these qualities are so connected with the detailed structure of the organ that in its absence they are imperceptible. And
3. with the appropriate organs in full working order what you perceive will still be a part conditioned by the position and past history of your body.

It is only in the case of sight and hearing that much progress has been made in correlating distinctions that can be perceived in those qualities that cannot be perceived without the organ with the structure of that organ.

    We can now at least be clear about the various relations with which we have to deal. There is firstly the relation P of an object to the mind when that object is perceived. And then there is the relation R between the object and the body which has been found to split up into the three relations r₁, r₂, r₃. The relation r₁ is that without the appropriate organ we cannot perceive qualities of a given sort. To this the main exception would be perceptions in dreams. r₂ is a relation involving the particular characteristics of qualities (e.g. the particular colour or sound). It is such that without certain distinctions in the structure of the appropriate organ we cannot distinguish these particular characteristics. The relation r₃ is between the position and past history of our bodies and what we perceive. The question is whether the fact that whenever objects stand in the relation P to the mind they also have the relations r₁, r₂, r₃ to our bodies is any reason for supposing that they cease to exist when they cease to stand in the relation P.

    With regard to the relation r, it seems to me tolerably obvious that it proves nothing. The fact that without eyes no one would perceive colours can be no reason for supposing that, granted that people have eyes and perceive colours, those colours cease to exist when they are not perceived. The possession of this structure might be the only way in which a mind that is connected with a body could perceive colours which would be there whether it perceived them or not. It is generally, and I think justly, held that there might well be sensible qualities that we do not perceive just because we have not the requisite organs. Electrical and magnetic qualities might perhaps be offered as examples. And there is a singular inconsistency in the position of a man who holds that the fact that without eyes we cannot perceive colours proves that colours are only appearances, and also holds that the fact that we dream about colours proves the same conclusion. When we dream about colours the objects of our dream perceptions are as coloured as those of waking life; the only difference is that we perceive them with our eyes shut. It is therefore an undue attempt to make the best of both worlds which proves that colours are mere appearances both because we can and because we cannot perceive them without using our eyes.

    But it will be said that it is not the fact that we must have appropriate organs in order to perceive definite sense-qualities that proves that the latter are mere appearances, but rather the necessity of the relation r₂. It will be said that this is a mere rhetorical flourish preparatory to the really fatal argument that when you have got the organs and thus are able to perceive the general qualities the perception of the particular characteristics depends on the detailed structure of the organ. But, taken by itself, this argument seems to be precisely in the same position as the argument from r₁. It is impossible to tell a priori whether the detailed structure of the organ is the condition by which the mind perceives real distinctions or whether it merely conditions the production of the perception of an apparent object with these apparent distinctions in it. Either explanation will account for the facts.

    The argument is often reinforced by considering how different the world must look to birds and insects with their eyes so widely different in structure from ours. It will be said: We have every reason to think that, even if there be something in common between what is perceived by all beings that have eyes, yet shapes, distances, and no doubt colours, will depend on the different structure of their organs. Think then how different must be the detail of what we perceive with our couple of movable adjustable lenses from what an insect perceives with an immovable eye consisting of hundreds of lenses set in different directions. What right have you to suppose that the object of your perception alone continues to exist unchanged when you cease to perceive it? There seems to be something in this argument which makes it worth while for us to consider precisely what it proves or renders probable, rather than hastily to reject all sense-qualities from the real, as is often done.

    As stated the argument is open to criticism. We are told in one breath that the internal structure of the insect's eye obviously differs very much from our own and also that for this reason it is presumptuous to suppose that the spatial characteristics that our eyes discover in their objects of vision hold when we cease to perceive. Well, if that be so, what reason have we for supposing that the insect's eye really does differ from our own? Our only reason is that it looks to differ; but then it is presumptuous, we are warned, to suppose that the distinctions that we perceive are those which exist when we cease to perceive them. Hence it is presumptuous to believe that the insect's eye really does differ from ours; but it was the supposed difference in the first instance that made it presumptuous to trust our own sight.

    The argument can, however, be freed from this defect. What it wants to be able to hold is that, whilst there is no particular reason to suppose that what I perceive is real, there is reason to believe that the perceived differences of structure between my eye and an animal's are marks of a real difference in structure. Although differences in the objects perceived may not themselves be real characteristics yet they may well be marks of real characteristics and this would be enough for the present purpose. When I perceive differences in the structure of two eyes and conclude that they must involve some difference in the characteristics of the objects perceived by means of them, I am not forced to believe that in order for there to be a real difference between the eyes at all it must consist in the reality of the perceived differences. It is enough that these perceived differences shall be marks of real ones. In that case I can conclude that the real structure of the insect's eye differs from that of my own and therefore that in all probability what he perceives is different from what I do. The premise on which this conclusion is based can be shown to be probable. When we have no information whatever about the nature of 'correspondence' between appearance and reality it will be improbable that two objects that look different will have the same reality 'corresponding' to them. For the corresponding realities can be identical in only one way whilst they can differ in an indefinite number. Hence, when nothing more is known except that the objects of one's perceptions are appearances, the alternative that what corresponds to two different appearances is entirely the same is only one alternative out of an infinite number. The real structure of the insect's eye might differ from that of our own in an indefinite number of ways; it could only be identical with it in one. Now the fact that the perceived objects differ certainly does not add to the already small probability that the corresponding realities are identical. Hence it seems fair to conclude that the perceived difference between my eye and that of an insect is a mark of a real difference in structure and therefore that it is probable that the insect does not perceive precisely the same object of perception as I do.

    Granted then that our experience does give us some good ground for supposing that insects perceive different objects from what we do in respect of detail, can the rest of the argument be maintained? The rest of the argument was that under these circumstances it was very presumptuous to suppose that what we perceive is real rather than the different object which the insect perceives. This is supposed to force us to the alternative that neither of the two objects is real. Clearly some further argument must be needed to prove this, since anything that has yet been offered leaves open the alternative that both are real even when we reject as unreasonable the belief that one is superior to the other in reality. Now the only ground for denying that both what the insect sees and what I see are real is the old one that we mentioned in the second chapter that we otherwise multiply real entities to a terrible extent. For the position is quite comparable with that of the innumerable different ellipses that we see as we move about when we say that what 'we really perceive' is a circle. The alternative then was open to us to hold that all these were equally real, but that each could only be seen from one position and that none of them could be felt. Here again it might be that both what we perceive and what the insect perceives are equally real, but that only minds furnished with eyes like ours can perceive the reality that we do, and only those furnished with eyes like insects can perceive the reality that they do. And once more I must insist that until you assume that all these perceptions of very similar objects have a common real cause there is nothing improbable in a world of reals, each of which can only be perceived by one creature from one place. Still, as we know, that is not the alternative that anyone adopts. We always assume that realities are dear and perceptions of appearances cheap and prefer to shape our theories of perception so as to lessen the former at the price of increasing the latter.

    What then I wish particularly to point out is that once more the relativity argument has proved powerless by itself to show that the objects of our perceptions are appearances rather than that the structure of our organs is the necessary condition of our perceiving certain special qualities and characteristics of reality. In the argument that we have just discussed it has merely succeeded in leading us back to the argument I(b) of our first chapter and in providing some new special cases to which to apply it.

    We have now seen how far the argument from relativity to an organ, in as far as it rests on a correlation between the observed structure of our organs and the characteristics of our objects of perception, is relevant to the question of realism. We have seen that all the facts are capable of two interpretations, viz. the Instrumental one which holds that our organs and their detailed structure are the instruments by which the mind perceives real things and their real qualities and characteristics; and the Causal one which holds that our organs and their internal structure are conditions of the perception by the mind of objects and distinctions in them, both of which for aught we can tell are mere appearances. So far the only means that has been offered for deciding between the two views is the old argument from complication of reals.

    Our next step will be to discuss these two alternatives further and to consider the extraordinary way in which science and common-sense divide up given masses of perceptions as between these two views. We may then perhaps hope to discover some principle of separation which we can criticise. Where correlation can be found between organ and object perceived common-sense will sometimes hold that the bodily conditions are what enable the mind to perceive certain characteristics that continue to exist whether they be perceived or not, and in other cases it holds that the detail is the actual cause of the detail in the object perceived and that the distinctions in the object cease to exist when we cease to perceive them. We will cite some examples and then try to discover some principle of distinction and to criticise it.

(i) The fact that we need definite organs to perceive definite qualities and that the perception of detail in the object perceived is found to depend in some measure on the structure of the organ is not generally thought by common-sense to prove that the qualities and the details perceived are mere appearance. It is rather held that the organ may be regarded as an instrument like a hammer or a chisel which the mind uses to perceive qualities and distinctions which are really present whether they are perceived or not. As we saw we only begin to doubt this when we consider that in all probability other creatures must perceive things as rather different from what we do, and that it is difficult to give any prerogative to our organs as telling either the whole truth or nothing but the truth about reality, and equally repugnant to believe that what each of us perceives is real but imperceptible to the other.

(ii) The fact that as we move our bodies about what we perceive is seen to change shape steadily is held to prove that we do not perceive the real; for it is held that in general these changes do not take place in the real that 'corresponds to' our objects of perception. Similarly the double objects that we perceive when we push our eyes aside are not supposed to be real. Thus this sort of dependence on the positions and states of our organs is supposed to prove that what we perceive is appearances and that the change in our organs causes them to alter, and not that the real alters and the changes in our organs are the means by which we perceive this real alteration.

(iii) The use of instruments on the other hand seems to be held to be comparable with that of the detailed structure of our organs and to be the means by which we perceive real distinctions which we could not perceive without them. Yet

(iv) not all instruments are supposed to do this. Some are believed to distort the real, i.e. to show us characteristics that are not there except as perceived. And the taking of certain drugs or excess of alcohol is supposed to have the same effect; i.e. not to reveal new details in reality but to make us perceive more appearances.

    Here we have a wide and difficult subject for discussion and criticism. We must first of all distinguish the Instrumental View from the rest. The Instrumental View refers to the relatively permanent structure of our bodily organs and holds that they are the means whereby our minds get at real distinctions. So far is this view carried that, unless the proper instrument be employed, what is perceived is not real. This is one reason why it is held to be obvious that what is perceived in dreams is unreal. 'You had your eyes abut when you saw this,' which would be the usual criticism of a dream perception would reduce to 'You were not using the instruments which everyone knows to be essential if you wish to see the real.' Of course there are other arguments about dreams which I have also discussed; but this would certainly be regarded as one important argument. The present view also holds that there are some additional conditions that the mind can usefully employ to help the bodily instrument, viz. certain arrangements of matter like microscopes. These, although not permanent conditions like the eyes and their structure, are yet held to be means of getting information about the real that could not be discovered without their help. Again, bodily instruments, like other instruments, are held to need adjustment and arrangement in proper positions in order for them to enable the mind to perceive the real. And this raises the difficulty of how we can tell when they really are in adjustment. And we also have to try and understand how it is that some instruments and some bodily motions can be known to help the mind to perceive the real whilst others can be known to make it perceive appearance.

    I think then that we can discuss the whole problem under the following heads:

1. Can we maintain that the bodily organs are instruments by which the mind can learn about the real in perception, and that the dependence of the perception of certain characteristics in the objects perceived on the detailed structure of the organ only shows that this detail is necessary for the perception of real characteristics and not that it is the cause of the perception of merely apparent characteristics?
2. Can we give a reasonable account of what we mean by these bodily organs being in proper adjustment which will enable us to hold that under certain conditions the objects perceived by them are real, but under others -- such as the pushing aside of the eye or the change of shapes with motion -- they are not real? And
3. Can we give a reasonable account of instruments of precision which will justify the view e.g. that an object seen through a microscope gives us new and true information about reality, whilst the universal yellowness seen after taking santonin does not?

    (i) The Instrumental Theory. First of all we must try to understand precisely what is meant by an instrumental theory of perception. We will begin by considering the analogy with tools, and see how far it holds. Let us consider a typewriter. This is a material mechanism consisting of parts so connected that by using it properly the hand can print letters on paper in any order that the mind chooses. The letters that are printable are correlated with differentiations of the typewriter itself. Now it is obvious that there is some analogy between an arrangement like this and an organ like the eye. The eye also is a differentiated structure; without it (if we set aside dreams) we can perceive neither visual extension, shape, distance, nor colours. With it there is strong reason to believe that some at least of the particular characteristics of these general qualities are correlated with certain differentiations of its structure. So far the analogy to the typewriter is pretty close. But now we must note some differences. (i) That effect of the typewriter's working for which we say it is the necessary instrument is produced in a third thing different both from that which employs the instrument and from the instrument itself -- viz. the paper. Now, in vision with the eye, on the assumption that the eye is an instrument by which we come to perceive reality, we must have quite a different arrangement. In the case of the typewriter there was

1. the mind and body of the typist;
2. the machine with its internal structure, and
3. the blank paper.

As a result of changes in a effects are produced in b which in turn produce effects in c which are correlated with the differentiations of b. In vision with the eye we seem to have

1. the mind,
2. the eye with its internal structure -- (we ought of course to include the brain and nerves, but the point is unimportant for the present purpose) --
3. the real object with its real differentiations, and
4. the effect, which is presumably the perception by the mind of the object with its differentiations.

But in the first case d was a change in c caused by a through the use b. Now in the present case this is precisely what is not supposed to happen. If the act of perceiving X changes X then it is not X that we perceive. In fact the change is supposed to be produced not in c but in a, i.e. in the mind that uses the instrument. If follows that, even on the instrumental view, the effect is a change in the mind, so that the instrumental view has at once some affinity to the causal one.

    The next point to notice is the peculiar nature of the effect. Knowledge and perception are of course unique events, and it is not to be expected that an example taken from material instruments used to affect the material world will furnish a complete analogy. Unfortunately there is not a general agreement as to the precise nature of the effect. The difficulty is that people are not agreed as to what they mean by a mind. But, waiving that difficulty, and supposing that we do know more or less what we mean by a mind even if we should be hard put to it to express our meaning in words, I suppose we could agree that the effect is what we call a perception and that a perception is something that can be analysed conceptually into a mind in the relation of perception to an object. It is an open question whether these terms can ever exist out of relations of that kind, but that of course is precisely the question that we have all along been discussing. All that can be said about the relation is that it must not alter the qualities of its referent otherwise than to give it the quality which it did not, if real, posses before, viz. that of being perceived, perceived, i.e. of being relatum to this relation. Some such view as this must I think be admitted. It must be noted that here it is hardly possible to call the real object a cause of the perception, except that it may be something in the object that causes a mind provided with the appropriate organs to enter into this relation to that particular object rather than to another at a given time. But this does not depend, I take it, on that particular character that it is perceived to have in distinction from other objects of perception; for all objects that are real and are perceived at any time must agree in possessing in them the causes necessary to set up the relation to the mind if those causes lie in the perceived objects at all. This is quite different from the case of the typewriter. There is not something already written on the paper, nor does something in the paper other than the writing set up a relation by means of the typewriter between the hand and the written paper.

    It is the belief in error that forces us to desert a purely instrumental view such as I have sketched. We have some reason to believe that we do not always perceive what really exists; at any rate if we believe it we have to deal with a terribly complicated world. Now the difficulty on the present view of the perception of appearances is obvious. They are not perceptions of nothing, but have an object just as much as do those which are supposed to be perceptions of the real. And the objects in both cases are clearly very much alike. The important difference is supposed to be that appearances, unlike real objects of perception, cease to exist when they cease to be perceived. But if perception by means of an organ just means that through its assistance mind and object are brought into the relation of perception to each other, this seems to imply that both are existing beforehand ready to be brought into that relation. And this cannot be so with apparent objects. The only way then to explain the perception of appearances on this theory would be to suppose that they begin to exist and enter into the relation of being perceived at one and the same moment. Now this is clearly the edge of a slippery slope. For now it seems as if the mind and its organs were, at any rate, the part-causes not merely of the entering of an already existent reality into a definite relation to the mind, but also of the existence of objects with their differentiations. If then the mind + an organ + perhaps some third factor are capable of causing not only the entry of realities into the relation of being perceived but also the existence of objects in that relation -- objects which cease to exist when the relation ceases to hold -- what ground can we have for supposing that any of the objects that we perceive are realities rather than that they are appearances caused in the second way, which is now admitted to be possible? In fact can you begin to distinguish between appearances and realities without making it very probable that we perceive nothing but appearances?

    Thus the instrumental theory comes to be replaced by a causal one. In the causal theory something X acts on the organ, the organ and the mind together produce a perception as a whole, i.e. something from which indeed an object can be analysed out, though there is no reason to think that it can exist out of that whole called a perception. Such an object is an appearance in our sense of the word. As soon as all perceived objects thus become appearances the analysis of the perception into mind + relation + object tends to be dropped and replaced by a whole called a state of mind in which the difference of object is attached as a kind of adjective. For, since all these objects are appearances, and cannot exist, as is believed, out of this relation to the mind, it is felt that the old analysis is otiose. This is of course harmless enough so long as it merely means that, whilst the distinction between perception and object perceived is clearly recognised, it is also recognised that it is only an analysis like that of a note into its pitch, intensity, and quality, and that the elements elicited do not exist apart. But in practice it is a most dangerous step because the undoubtedly important difference between object perceived and perception of object, which remains on any theory, is minimised until it is thought that because the latter is mental the former must obviously be so too.

    But we have been running ahead of common-sense and must now return to it, The replacement of the instrumental theory by the causal one is very slow and tentative, and common-sense believes that it can distinguish between cases where the instrumental theory still holds and others where the causal one becomes necessary. Let us consider the steps that common-sense makes.

1. The instrumental theory is believed at first to be sufficient for the ordinary perceptions of everyday life, and only mirages and bent sticks and such objects are held to require the causal view.
2. Further investigation shows that what different people see at the same time and what the same person sees at different times from different places often closely resemble each other and yet have discoverable differences. The likenesses and differences seem easily explicable on the causal theory by the assumption of a common cause and slightly different conditions. Hence the causal theory begins to spread at the expense of the instrumental one.
3. Speculative persons now suggest that in all cases what we perceive are appearances but that in true perceptions the objects perceived are like the real non-mental non-organic causes of these perceptions, whilst in illusory perceptions they are not.
4. Finally it is asked: What possible reason can there be for supposing that the causes of our perceptions in any way resemble the effects?

Thus we reach the thing-in-itself. Ordinary common-sense wavers between (a) and (b); orthodox science (apart front Mach's school) wavers between (b) and (c). (d) is held with varying degrees of consistency by Kant, Spencer, and Huxley; but efforts have always been made to get away from it and to offer some further determination of things- in-themselves, e.g. the Will in Schopenhauer and the noumenal self in Kant. Common-sense apparently never supposes that the causes of our perceptions are past states of ourselves or of other minds. This alternative, according to the way in which it is worked out, leads to Solipsism, Phenomenalism, or Idealism.

    We must now consider the position that the organs of perception are the mind's instruments a little further, and show some other distinctions between them and instruments like typewriters which are used by the body and the mind. In all use of instruments the user is supposed to be a substance and active. We saw that we could make little use of the conception of activity and that there were difficulties about substance except for objects in space. This view then will assume that the mind is a substance and active. By its activity we can only mean, after our discussion on causality, that events in it are part-causes of an effect. The effect here is however a change in the mind, as we have seen. Hence we have to distinguish

1. the change in the mind that caused it to use the instrument and
2. the change that this use of the instrument causes in the mind that uses it.

All ordinary instruments like typewriters are voluntarily employed, thus, in their employment there are on the instrumental view of the bodily organs two separate uses of instruments --(i) the mind uses the body (here by means of volition) and (ii) the body uses the typewriter. We have to consider the first of these. In the use of organs by the mind for perception the use may be voluntary or involuntary. There are a good many perceptions that we cannot help having. On the other hand it is clear that the use of our organs is also in part voluntary. The volition enters when we voluntarily place and adjust our organs and when we pay attention. It is only in such cases as these that the mind's use of organs of perception is strictly analogous to the use of a typewriter. We voluntarily do certain things with our bodies just as we do with typewriters because we have reason to believe that the result will be one which we wish and cannot reach without the use of such helps. But, whilst typewriters will not work of themselves, i.e. someone must wish to write in order for them to write anything, minds can and do have perceptions by means of their organs even when they do not wish to do so. When the reference to volition as an antecedent to the use of the instrument is cut out a good deal of the analogy between our organs and instruments seems to vanish. We must now say that the same mind which can use bodily organs to produce changes in itself called perceptions may also have those changes produced in itself by the instruments without having previously willed to use them. Now we know that, in the case of perception, the perception that is finally produced is an effect in the mind; but what was essential to a purely instrumental view was that the mind + the organ should also condition the perception. On the view of perception as a relation between mind and object the mind could only be said to be a cause in the sense that it depends on its nature that the relation of perception can be set up between it and anything else. Now even when our having a certain perception can be said to depend on our past volitions the immediate effect of those volitions is merely to adjust our organs and put them into definite positions. After that what we perceive does not depend, so far as we can see, on any other volition. But, for complete analogy between the use of an instrument by the body and that of an organ by the mind, it would seem, as we saw, essential that the mind should be 'active' in using the instrument, and that would mean that all the time it was being used events in the mind were going on and were part- causes of the effect. We see however that there is no evidence that this is the case either with voluntary or involuntary perception. In the first place, for the present purpose the former reduced to the latter, because, as we saw, the whole effect of volition is to produce a preliminary adjustment of the organ after which everything proceeds involuntarily. And in this involuntary process we cannot discover that the cause of the perception is the comparatively permanent structure of the organ + changing states of the mind. As far as we can see the mind only enters as a kind of permanent condition in the sense that it is the sort of thing which alone can be referent to the relation of perception. Thus the analogy between perception by means of an organ and the use of an instrument like a typewriter breaks down over the fact that the user in the first case is not and in the second case is continually 'active' while he uses the instrument. The view with which we seem to be left is that organ + mind are joint conditions with some other cause of the mind entering into the relation of' perception to an object.

    What however was the essential element in the instrumental view from the standpoint of the theory of knowledge? It was that the use of the organ gave us true knowledge about reality which we could not get without it. Now this possibility is not affected by the distinction that we have just noted between the way in which minds use organs and the way in which they use typewriters by means of bodies. Suppose that the organs + the mind are joint conditions with some other cause of the establishment of the relation of perception between the mind and some object, then the important question for the theory of knowledge is not directly what that third part of the cause may be, but whether as a matter of fact the term to which the three in conjunction cause the mind to have this relation is a real thing or an appearance. It would not be necessary in order that perception should give knowledge of the real that the third condition of the perception beside the organ and the mind should lie in the reality which is perceived in that particular perception. Yet common-sense has rarely accepted any other alternative. It has always wanted the cause to be like the object of the perception that it causes, and, in as far as it has failed to be so, it has held that object to be appearance.

    We must take a less timid view however and put our question about the revised form of the instrumental theory as follows: Granted that the mind and the structure of our bodily organs are joint conditions which in combination with some other cause bring the mind into the relation of perceiving an object, can we discover (a) Whether that object is real, and, if so, when? and (b) What are the natures of the causes in particular cases?

    Now common-sense in its own theory of knowledge has an answer to both these questions. In its less reflective form it says: (a) Nearly all the objects with which we enter into the relation of perception are real; but some are appearances (b) When our perceptions are perceptions of the real the cause of our perceiving just this thing at this moment lies in the reality which we perceive together with the joint conditions that we have the appropriate organs and a mind. When we perceive an appearance the cause cannot be in the object of that perception, since that did not exist until the perception itself did so. It must therefore lie in other things which we do not perceive at the moment when we perceive the appearances. This seems to me to be the theory of knowledge of reflective common-sense, and, as it is carried over, in part at any rate, into natural science, we shall do well to examine it carefully.

    This theory enables common-sense to give some account of the various ellipses that are seen from various positions and the real circle which it believes to be there. The real circle, it will say, has in itself the cause of our perception of it when combined with other relatively permanent conditions. The ellipses that are seen from other positions are appearances and, as such, it cannot be events in them that cause our perception of them. On the contrary it is still events in the real circle. These have remained the same but the conditions have changed slightly and therefore it is only to be expected from our general knowledge of causal laws that a slight change in the effect will be produced such as is observed. This then would be the way in which common-sense would fulfill its favourite maxim that 'realities are dear and appearances cheap' on the present view. We shall have later to consider whether this particular argument is justified even on its own premises.

    At present however we will consider generally the view that we have attributed to common-sense. That view depends on the synthetic proposition that when real things are perceived events in the real things are part-causes of the perceptions of them, the other conditions being (a) a mind, and (b) bodily organs properly constructed and adjusted. Is such a synthetic proposition true, and, if so, could we ever have been led to discover its truth?

    The first point to note is that it contains two synthetic propositions.

1. Certain objects of perception have events in them which are causes of those objects being perceived; and
2. All objects that are real and are perceived have the perceptions of themselves caused by events in them.

It leaves open the question whether there are real things that are never perceived, but common-sense would certainly hold that that was possible and probable. We have to enquire then whether these two synthetic propositions are true, or whether it is possible to get the sort of evidence necessary to prove or render them probable. They are certainly not self-evident, so that unless they can be rendered probable by some other propositions we have no particular right to believe them. We may therefore begin by asking whether there is any way of proving or rendering them probable.

    Causal laws can only be elicited by observation either of the sequence of events which we finally decide to be cause and effect, or of other sequences which we analyse so that the causal law in question emerges as a product of analysis, or as a hypothetical law between what is not observed which what is observed renders probable. Now it is quite clear that we cannot observe first certain events in X and then note that later on we perceive X, for that would be to imply that we can observe parts of X before we observe any of it, which is absurd. Hence, if the causal law be one of succession it cannot be discovered by observing the succession directly. If the causation be contemporary it would be theoretically possible to observe directly that conjunction of events which might encourage a belief in a causal law. For we might observe that there was always a definite process going on in all objects that we perceive so long as we perceive them. But there would be very little comfort to be got out of this. In the first place we do not observe anything of the kind. And further, if we did, we certainly could not base a law of simultaneous causality on this alone; we should also want to know whether the same process might not be going on in the things when we did not observe them. And we clearly could not decide this point by observation, since we cannot perceive what things are doing when we do not perceive them.

    It is perhaps worth while to note that if we are dealing with successive causation the converse of (b) will follow from (a). If there be any objects of perception, the perception of which is caused by events in those objects that happened before the perception took place, then it is clear that such objects must be real. For they must have existed before the perception of them took place in order that they should have states before that event, and if they were appearances this would be impossible. If the causality be simultaneous this will still follow. For the event in the object will then take place at the same moment as the perception, if it be the cause of the latter. But an event cannot be said to take place in anything unless that thing has existed for a finite time², and therefore if an event in an object be a cause even by simultaneous causality of the perception of that object the object must have existed for a finite time before it was perceived, and therefore be real. The same will hold if we allow the cause to follow the effect, though common-sense does not generally admit this possibility. For if an event in X be a cause of a previous perception of X, then X must exist after the perception of X, and therefore cannot be a mere appearance. If we allow an interval between cause and effect we must be prepared to admit that a mind may perceive an object either before it has begun or after it has ceased to exist. There is no particular objection to this. Common-sense would indeed reject the former alternative, but it holds that the latter often occurs, and, as far as I can see, there is no difference in principle involved.

    After this digression we can return to the question of how it is supposed that we actually learn about the propositions (a) and (b). It will now be admitted that we cannot hope to discover by direct observation the causal laws whether simultaneous or successive that connect events in what we perceive with our perception thereof. The only possible method then must be the hypothetical one. Now we are also told by science that the cause of our perceptions of objects is imperceptible events in imperceptible parts of those objects if real. Science would certainly hold that the perceptions of dreams are appearances, and as we saw would probably give as one reason for this opinion that they are not perceived by means of the appropriate organs. But, if pressed as to why this should matter, I think it would almost certainly reply that as the organs are not used we must assume that dreams are due to central excitations, which just means that they are caused by our own bodies. And, if it be asked why perceptions completely caused by states of our own bodies should not be perceptions of real objects, I think there can be no doubt that science would answer that it is because the object of our dream perception is not a part of that body whose changes cause the perception. Thus there seems to be no doubt that science does in some way accept the common-sense view that the perceptions of real objects must be caused by events in those objects, although it cannot be quite so naïf about it as is common-sense.

    It will be best then to formulate the theory under discussion in terms of the beliefs of science since we see that they only differ from those of common-sense by their greater elaboration and more consistent application of a common principle. We must then (1) formulate the position which natural science takes up on this matter, and (2) see whether it is a subject to which the hypothetical method really applies.

    (1) We know roughly that science believes that extension, figure, mass, and motion are real, and that it believes itself able to prove, or at any rate to render very probable, that the causes of the perceptions, both of other qualities which it believes to be appearances and of those qualities which it believes to be real, are the motions of small extended masses with electric charges. It is true that so far, without introducing causation, we have seen no reason whatever for ascribing a superior reality to the so-called primary rather than to the so-called secondary qualities, whilst, with such a theory, it remains a question whether either can be said to be real. However, we will set this difficulty aside for the present and consider the exact sense in which science believes that when we perceive a real object the cause of the perception of it is to be found in changes within it. In the first place, if chairs and tables really consist of little extended bodies in very rapid motion, can it be said that I ever perceive anything real, since I certainly do not perceive anything of this kind when I look at a chair or a table? If we throw away at once at the bidding of science all secondary qualities, this awkward question will still crop up with regard to primaries. I think that science would answer: You do not indeed perceive all that is real, nor indeed are all the particular shapes and sizes that you perceive real, but as far as concerns primary qualities, all that you perceive when your organs are properly adjusted either is real or is related according to known laws with real primary qualities. The chair that I see has a certain shape and size; subject to certain modifications, that remain to be discussed and are connected with the change of shape and size through change of relative position and adjustment of our organs, science would hold that we do perceive the real shape and size in a certain definable sense. That is to say, that, while we do not perceive the differentiation into electrons in rapid motion, yet the limits within which the electrons are moving about are practically those that are seen with the naked eye. Again, if the chair visibly moves, we do not indeed perceive the motions of individual electrons, but all the electrons are moving in the direction of the perceived motion of the chair as a whole, retaining the old geometrical outline. It is in this sense, then, I take it, that the primary qualities that we perceive under certain conditions with our organs are real.

    We can now understand in what sense science means that when we perceive what is real the cause of our perception is events in the reality that is perceived. It means that the cause is events in the real which are not themselves perceptible, but are changes in imperceptible parts of that whose real shape, size, and motion as a whole we are caused to perceive by these events. This is an intelligible statement, but in it the view of common-sense is beginning to lose its simplicity. It will be noted that on the ordinary scientific view the instrumental and the causal positions are combined in the perception of an object. The events in that object are supposed to bring us really into perceptual relation with some at least of its primary qualities, and the eye is a necessary means to this end. But they also are supposed to cause states in our eyes which cause perceptions of colours, and the objects of these perceptions are mere appearance. If we had not properly constructed eyes we should not perceive either shapes or colours; but the second would not rob us of any knowledge about the real on this theory, whilst the first would. I think, however, that even among secondaries science would draw some distinction. It would almost certainly hold that the colours perceived on real tablecloths were in some way more reputable than those perceived in dreams, on the ground that the cause of the former was events in that of which there was a perception, whilst this is not so in the latter. I do not think, however, that anything can be made of such a distinction. Once a quality is believed to be an appearance it is surely impossible to smuggle back a kind of reality for it which is reflected from one of the other effects of the cause of our perception of it.

    The final position of science then would seem to be that the perception of what is real must be caused by events in that real thing, but that those real events also cause the perception of appearances which may (as in the case of colours) or may not (as in that of sounds) be localised in that real thing by the percipient.

    (2) As we now understand the position that science takes up as to the relation between the real and the causes of our perceptions of it, we can pass to the consideration of the method by which science claims to discover these imperceptible causes and hypothetical laws in the case of our perceptions both of appearances and of realities.

    The method as we saw must be in the end hypothetical. Science has to establish two things: (a) That when we perceive the real there are differentiations in it that we do not perceive, and (b) The nature of the psychophysical laws connecting the imperceptible changes of these imperceptible realities with our perceptions. With regard to the laws, we ought to note that certain things can be discovered before we make any particular theory as to the nature of the more remote causes of our perceptions. These have indeed already been mentioned in part at any rate. It is independent of any particular theory that without eyes we cannot see colours and shapes and that therefore bodily organs are in general necessary for the perception of the distinct general qualities, whether they be real or only appearances. Again, the fact of perceiving similar things in dreams, and the results of lesions of the brain and nerves suggest that the last stage in the process would be a state of brain, and that when we do perceive by using organs, the organs have states which affect the brain, and the states of the brain are the last cause of the perception, both of appearances and of realities. Thus without any special theory about the nature of the complete causes of our perceptions, it looks as if we could distinguish three kinds of causal laws which successively operate in the causation of our perceptions. These would be

1. Physicophysiological laws which deal with the causation of the variable states in the relatively permanent structure of our organs;
2. Physiological laws connecting the states of our organs with the final states of our brain; and
3. Psychophysiological laws connecting the final states of our brain with the differentiations of the object the perception of which they cause.

When we do not want to refer to this probable analysis of the total process we shall just refer to the whole process as Psychophysical.

    What particularly interests us at present is the evidence for the physicophysiological laws, but it is hardly possible to consider these alone and apart from the total process. It is clear that our evidence must in the end rest on what we do perceive. Now all that we can be fairly sure about without hypothesis is the necessity of organs of a certain definite structure for us to be able to perceive certain general qualities at all. But of course we never do perceive qualities in general, but particular cases of them, and we perceive now one particular case and now another; now a green circle and now a red triangle. If we accept the instrumental view we are not forced to believe that there is a different bodily state for every different particularisation of general qualities that we perceive. The eye with its special structure might be essential to our perception of colour and shape and extension of any kind, but it might well be that when once we had the structure requisite for this we could perceive a red triangle and a green circle without there being any special state of body corresponding to red and green, to circle and triangle. Something would bring a mind capable of perceiving colour and shape now into perceptual relation with a red triangle and now to a green circle, and there would be an end of the matter. On the other hand, this is not the type of view that science tends to adopt as it advances. It expects to find not merely that a permanent structure of the organs is necessary for the perception of general qualities, but also that to every particular difference perceived there will be a different state in the organ. Thus it would expect to find that the eye really was in a different state when it perceived a red triangle from that in which it is when it perceives a red circle. It is clear that a great deal in this view must be as hypothetical as anything in the purely psychophysiological part of the process. No one can observe that there is a different state in the eye and finally in the brain for every different particularisation of every quality that is perceived. Still as time goes on some direct evidence is found. We can more or less correlate the accommodation and convergence of our eyes with the distance at which we perceive objects and prove that in their absence objects can only be perceived clearly at a single distance; and we can correlate, though with less certainty, the fibres of Corti with the hearing of notes. Still in the main the further developments of the physiology of the sense organs and their laws must be as hypothetical as electrons and the laws of light-transmission.

    Now when we have got beyond what we can actually observe it is clear that from the same data, viz. our perceptions and their observed qualities, we have yet to substantiate two sorts of hypothetical entities at least and three sorts of hypothetical laws at least. Any perception will involve the hypothetical causes of the states of our organs and their laws; the hypothetical imperceptible states of our organs and of the brain and their laws; and the hypothetical laws connecting the states of our brains with the objects that they are supposed to cause us to perceive. We have, in fact, a large number of unknowns to determine from one set of knowns, viz. our perceptions and their sequences. It is clear, then, that there can be no perfectly determinate solution of the problem. You can make up various laws and various entities, and by suitably connecting them account for the facts. Still, if one theory can be set up whose assumptions are not intrinsically improbable, and which does account for the facts that can be observed much better than any other, and also intrinsically quite well, we may fairly assume that it is very probable.

    In some measure this seems to be possible. For instance, we can tell by actual observation that certain permanent general qualities in what we perceive can only be perceived by people who have a certain perceptible organ and with a perceptible structure of a certain kind. And still keeping to the perceptible, we can carry such correlation a good deal further with great probability. Now, if we can assume that what we cannot perceive resembles in the main what we can and do, it is fair to hold that an hypothesis that carries such a correlation between the structure of our organs and the ability to perceive details still further, is intrinsically quite probable, and, if in company with other intrinsically probable hypotheses, it accounts well for what we do perceive, the total system will be probable, and will reflect an additional probability on its parts.

    So much for physiological hypotheses and entities. Again, with regard to physicophysiological ones, subject to the same assumption of the probability that what is not perceived is like what is perceived, we may build up an initially probable hypothesis about the physical causes of the physiological changes that end in perceptions; and this, when combined with our physiological and psychophysiological hypotheses, themselves supposed intrinsically not improbable, will account so well for what we do perceive that it will furnish a probable theory and will reflect an additional probability on its elements. For instance, we might run very rapidly over the scientific arguments for the wave-theory of light to show the kind of argument with which we have to deal. It would go somewhat as follows:

1. It is a matter of direct observation that when we hear a sound we can generally find a vibrating body which we can see and feel to be vibrating.
2. Another essential element is a medium between the body and the ear, and it can be shown that we only hear the sound after a definite interval from the beginning of the vibrations which depends on the distance and the nature of the medium.
3. There are a great many phenomena with regard to colours which can best be explained by supposing that the cause of our perception of them is also a vibratory disturbance; but the absence of a material medium is not found, as in the case of sound, to stop the experience altogether.
4. There are numbers of phenomena which can be easily explained on the assumption that bodies are more differentiated than they appear to be, and only with great difficulty without that assumption.
5. On the assumption that little imperceptible bits of matter and little electric charges obey the same laws as larger perceptible ones, there is good reason to believe (a) that little charged particles exist in bodies under certain conditions, and (b) that when they vibrate they will emit periodic electric and magnetic disturbances that will travel with a calculable velocity, and will be executed at right angles to their direction of propagation.
6. Experiments make it probable that light also travels with the velocity, and the effect of magnetic fields on polarised light make it very probable that the periodic disturbances mentioned in (v) are to be identified with light, and are the cause -- together with the structure of our organs --of our perception of colours and shapes.
7. Just as it is practically certain from experiments with Savart's wheels and with sirens that the pitch of notes that are heard depends on the number of vibrations that reach the ear per second, so we find that many otherwise inexplicable phenomena receive an elegant explanation when a similar assumption is made as to the connexion between perceived colours and periods of vibration of light.

    Such, then, in the roughest outline are the arguments on which science founds its particular theory as to the causes of our perceptions. It will be seen that to be plausible the arguments must assume that what is real but imperceptible resembles that which we perceive. If primary qualities be real, then it is very probable that what we perceive is more differentiated than it appears to be, and if the imperceptible obeys the same laws as the perceptible, then it is very probable that the account which science offers of the mode of production of our perceptions is correct. On the other hand, unless we have reason to believe that, at any rate with regard to primary qualities, the result of this whole complicated process is actually to make us perceive the real, even if it only enables us to perceive a part of what is really there, the whole theory becomes meaningless as it stands, and must either be rejected in toto or replaced by some very complicated set of further propositions. Unless, for instance, what we perceive as extended really is extended, it is certainly not obvious what could be meant by saying that the perception of it was caused by the imperceptible motions of imperceptible parts of it. The question, then, as to whether we accept the instrumental view which holds that all this causal process ultimately ends in the perception by the mind of something real, or the purely causal view according to which it merely causes us to perceive an object which is an appearance, and allows no conclusions about the real further than the conclusion that it is able to cause perceptions of this kind, is no academic one, but is vitally important to science. Once grant that science is right in taking the instrumental view with regard to the perception of primaries, and it can go on its way rejoicing, and everything that it tells us will be a real contribution to cosmology. But deny this and its eminently successful theory will have destroyed its own premises, and the attempt to restate it in terms of the new situation must be laborious, and may well be unsuccessful. But before we come to this vitally important point as to whether science can justify itself in retaining just so much of the instrumental view as it does and replacing it everywhere else by a causal one, we must consider a little more closely the position which science takes, that when we perceive a reality the cause of our perception is to be found in it.

    If it be true that the perception of all that is real in an object perceived is caused by events in that reality, the position of science as to the unreality of secondaries might seem to follow logically from its statement that the perception of secondaries is caused by states of primaries. For if 'P is real' implies that the perception of P is caused by events in P itself, it must follow that if the perception of P is not caused by events in P itself then P is not real. Such an argument, though formally valid, would be illusory in the present case because it depends on an ambiguity in the word 'in.' No doubt if the scientific theory be correct the perception of red is caused by the motions of imperceptible bodies, and with respect to the causal laws involved, nothing is mentioned except their primary qualities. That, however, is not surprising. The observed laws of mechanics are always stated in terms of primary qualities, simply because it is observed that it is practically³ indifferent to them what colours the bodies may have. We have no ground for denying that the little particles whose motions cause the perception of a red body may be red. It will entirely depend on whether we hold that the effect of the wave-motion on the eyes and brain and mind is to bring the latter into relation with the real colour or merely to produce a perception with an apparent object, viz. red. Unless you first deny the possibility that the motions, which as a matter of fact cause you to perceive red, are the motions of red bodies, you cannot hold that the fact that without those motions you cannot perceive red, and that the laws of them involve no mention of redness proves that they cannot be red. In fact, you cannot be sure that the perception of red is not caused by events in what is red until you know that they are events in what has merely primary qualities, and therefore you cannot use the scientific theory of the causation of perceptions to disprove the reality of colour.

    But is there any reason to accept the scientific view that when we perceive something that is real the events that cause that perception are to be found in the reality that we perceive? A priori there is certainly no very good reason, so far as I am aware, for such a belief. When we perceive a definite reality, the event whose causation we are seeking is the establishment of a relation between the mind and that reality. Certainly on the ordinary view of causation this event must have a cause; but I know no reason why that cause should be found in the reality which is relatum to this relation. If I throw a stone through the third ground-floor window on the right of the Great Gate, the cause of my throwing it through that window may have no connexion with events in the window or the room beyond. It may just as well be because someone jerks my arm at the time, or because I believe that three is a sacred number. I think that the best reason that science could offer for its belief would be that the assumption of it seems to lead to a general theory that is better in accord with the observable facts than any other that can be suggested, whilst it is not intrinsically improbable if we suppose primary qualities to be real. There is, however, a further reason which makes this suggestion an intrinsically reasonable one. When we perceive a real thing the effect is a setting up between it and the mind of a certain relation. It is held that for this to happen a mind, a certain kind of organ, and an event of some sort are necessary. The question is: What sort of event and where? The reason why an event is wanted at all is because our perceptions begin and end, and we perceive now this and now that. Granted, then, that we knew the type of event required, we should still have to ask why the relation set up by it between the mind as referent and a real object as relatum should have now X as relatum and at another time Y. Yet this certainly happens, and therefore it seems as if the nature of X and Y ought to enter somewhere into the statement of the causal law. Now, of course, it need not be the case that the particular way in which X and Y enter should be that the event is in X when X is perceived, and in Y when Y is perceived; but, since the position of the event is as yet undetermined, and since it is certain that X and Y must be mentioned somewhere in the causal law, it is certainly reasonable as an hypothesis to locate the events in X and Y respectively, and to say that when a real thing is perceived the event that causes us to begin to perceive that thing is an event in it. When once this is done we build up on that probable hypothesis the scientific theory that the cause of the perception of both primary and secondary qualities is to be found in imperceptible events in imperceptible parts of what we perceive in this particular perception. And in so far as the theory, founded on this initially reasonable assumption, is found to account for actually perceived phenomena under various circumstances, the initially probable assumption has its probability strengthened.

    We can now sum up the scientific position and the arguments for it, including those by which it holds itself to be justified in rejecting secondary qualities.

1. There is reason to believe that our successive perceptions depend jointly on our minds, the permanent structure of our bodily organs, and on some variable event whose location is as yet undetermined.
2. In the perception of the real the effect of these causes is to establish a relation between the mind and some particular reality that is perceived.
3. Since we sometimes perceive one object and sometimes another and this only partly depends on our own volitions, it will follow that, if our minds ever enter into this relation with real objects, a complete law of the causation of our particular perceptions will have to take into account those qualities or relations of the reals in question which determine why the mind is related now to one and now to another.
4. Since the position of the event, which is a joint cause of the perception according to (a), has not yet been defined, it seems probable that we can satisfy (c) by locating it in the particular reality which it causes us to perceive.
5. When we make this assumption and try to determine the nature of the events in question, we are led by ordinary scientific arguments to the view that the causes of our perceptions are motions of imperceptible pieces of matter contained within the boundaries that we actually perceive.
6. But the laws at which we arrive not only do not require us to take into account the secondary qualities of these imperceptible particles, but also account for the perception of the secondary as well as of the primary qualities.
7. Hence not only is the probability of our initial assumption that our perception of the real is caused by events in the realities that we perceive strengthened by the agreement of the theory based on it with the facts, but also, since that theory accounts for the whole of what we perceive by events which are only known to have the characteristics of part of it, there is no reason to suppose that the remaining characteristics of what we perceive are real.

    We must now criticise this argument. It is obliged to hold that primary qualities are real. Its troubles spring from the fact that it certainly does not believe that all perceived primary qualities are real and that it holds that no secondaries are so. A purely instrumental theory or a purely causal theory does not suffer from such difficulties. Their special difficulties are that the one gives us a great deal more reality than we want, whilst the other makes the undoubtedly successful scientific theory difficult if not impossible to state consistently with its conclusions.

    We have already said something about the scientific argument against secondaries. But we merely showed there that the scientific theory, even if fully accepted, does not make it impossible that there should be real secondaries, and that the mechanism of the wave theory should be the one way by which we are able to perceive them. But the argument in (g) above against secondaries is rather different. It is not directed to proving that they cannot be real, but only to showing that there is no reason why they should be so. Let us consider this argument. It simply rests on the fact that, whilst the theory as to the causes of our perceptions of primaries has to be stated in terms of primaries, the theory of the causation of the perception of secondaries does not explicitly demand any more than primaries and events in them. Now we have indeed seen that it is utterly impossible to conclude from such an argument that bodies are not really coloured; but, for all that, it might be held that if we accept the general theory there is a stronger reason for believing in the reality of primaries than in that of secondaries. For unless some primaries are real the theory as stated falls to the ground, whilst on the other hand it would he perfectly consistent with the theory --though not, as is so often believed, a necessary consequence of it -- that all secondaries were mere appearances. Still there is one consideration which is relevant and must be noted. We cannot confine the supposed real qualities to extension and figure and number. We only experience extended colours or temperatures or hardnesses, and I fail to see what right we have to apply laws which have been obtained by observing extended bodies that always had other qualities beside extension to mere extensions. I think then that we shall have to conclude that the theory that makes primary qualities real must also accept the reality of some other quality related to extension in the same sort of way as are colours and temperatures. That quality might not be a colour or a temperature, or, if it were, it might never be the colour or temperature that we perceive. But, as we have seen, there is so far no independent argument to make us take the instrumental view for primaries and the causal view for secondaries, so that when it is once granted that the instrumental view must be taken for at least some primaries there is no good reason for not taking it also for the perception of at least some secondaries, and supposing that sometimes at any rate the result of all the complicated mechanism of the wave-theory and the eye and the brain, is to bring us into direct perceptual relations with real colour.

    It ought to be noted that the same positive argument does not apply to sounds. I do not think that it is possible to prove that the instrumental view is not sometimes true of them as well as of colour, and that the vibrating bodies and the waves and the complex structure of the ear are not the means by which the mind perceives what would still exist whether perceived or not. But, on the other hand, whilst all that is extended has colour or temperature or 'feel,' all that is extended is not sonorous. Hence there is no positive reason for believing that the perception of sound is any more than an effect of the motions of perceptible bodies, and the perception of a mere appearance.

    The crux of the whole question then really is whether we can keep the instrumental view for the perception of primaries. If so we can keep the scientific theory as in essence true about a large part of reality. There being no a priori reason why we should not accept the reality of primaries merely on the ground of relativity to an organ, the difficulty springs not from this relativity, but from the fact that neither science nor common-sense believes for a moment that the instrumental theory applies to most of the primary qualities that we perceive. Science is perfectly convinced that most of the shapes and sizes that we perceive are not real, but are appearances more or less like the reality. And here it has clearly dropped the instrumental theory altogether.

    We must therefore consider the cases in which it is believed and those in which it is denied that we perceive real primary qualities, in the hope that we may be able to justify the distinction that is drawn. In fact we have got to answer the question that I asked in p. 200 of this chapter: 'Can we give a reasonable account of what we mean by bodily organs being in proper adjustment, which will enable us to hold that under definite knowable conditions the objects perceived by their means are real, but that under others, such as the pushing aside of the eye or the change of shape due to motion, they are not real?' All the arguments of any weight against primaries practically come to the assertion that we cannot make this distinction. Thus we have to consider our old friends the successive ellipses seen instead of an object which is believed to be really a circle, and the second object seen on pushing aside the eye, and the visions of sleep and drugs. The realist view seems to be that in the main we can distinguish; that, although under many circumstances what we perceive are appearances, yet these can not only be known to be such, but can also be connected with the reality by known laws, so that its qualities can be discovered from theirs.

    The idealist argument would be: You perceive shapes and sizes, and as you change your position they alter slightly. You do not believe that all these successive qualities are real and yet you do believe that primary qualities are real. But what ground can you possibly have for your conclusions about real primary qualities except what you do perceive, which you admit to be appearance, and all of whose observable laws must be laws of appearances? With regard to the visual perception of three-dimensional objects the case is still more paradoxical, as Mr Prichard⁴ points out in his able book on Kant. We believe that there may be real spheres, yet we are equally certain that if there be real spheres what we see when we say, in our crude way, 'that we perceive a sphere' never is spherical but is ellipsoidal.

    This must necessarily modify the instrumental view of knowledge. It will now not be able to say in general that in the perception of real primary qualities some event in the real makes us perceive that real. In the case of the three-dimensional bodies we never do perceive the real, and therefore, if the event in what we believe to be real causes us to perceive anything, it is at any rate not the real. It will have to be modified somewhat as follows. In many cases we cannot perceive the real object, events in which are the joint cause with our bodies and minds of our having the perception. In fact, in the case of seeing three-dimensional objects we never can perceive the reality. But the characteristics of the appearance that we do perceive depend jointly according to discoverable laws on

1. real events in the reality that is said to 'correspond' to the appearance,
2. on the real primary qualities of the reality,
3. on the real relative spatial positions of the organ and the reality, and
4. on the state of the organ and the mind.

We must note how very different in principle this is from the old instrumental view. In that view we could perceive realities, and, when we did so, the effect was the establishment of a relation between the mind and a pre-existing reality. No question of likeness of cause and effect arose; for nothing could be more unlike the cause (viz. events in the way of motion of imperceptible parts of the reality perceived) than the effect (viz. a relation between the mind and the reality). But here the question becomes a very pertinent one. If you never perceive the reality but only appearances, which, with the perceptions of them, are caused as wholes by events in the reality, how do you discover those laws which enable you to judge, either (a) that the reality has primary qualities as the appearance has, or (b) that the particular primary qualities of the reality can be deduced from those of the appearance? Here you do seem to be assuming quite unjustifiably as you did not do on the old statement of the instrumental theory, that one aspect of an effect must resemble the thing in which the events that caused it took place.

    Is there any way out of this difficulty? I think the first point will be to investigate its premises a little more closely. The essence of the argument is that with three-dimensional bodies you say that you never perceive the reality, and therefore it seems impossible to see how you can be justified in your further assertion that you know how the qualities of the reality are connected with what you perceive. One important point is that so far the argument has offered no ground for doubting that extension and figure of some kind are real. I may shift about from place to place keeping my eye (as we say) on the same object, and I may observe that it changes in shape; but I never observe that it ceases to be extended and to have a shape. Now it seems to me that this is a very important fact for the present purpose. We know that if primary qualities be real at all, they cannot just be shapes in general and sizes in general, but must be particular shapes and sizes. Moreover we have now seen that the present argument at least gives us no reason to doubt the existence in reality of the general quality, and therefore of some (though, it may be, unknown) particulerisations of it. Hence if we find general laws connecting the shapes and sizes of perceived figures we may be able without undue presumption to gain some knowledge of the shapes and sizes of real figures that correspond to what we perceive.

    Before, however, we work out this consideration any further it is right to notice an alternative that common-sense and science do not accept, and, as far as I know, do not discuss. This is the alternative that the circles and ellipses really do alter in shape as we move relatively to them. After all why should not our movement be a cause of their change of shape according to definite laws just as well as our squeezing them with our fingers if they chance to be made of some bendsome material? In that case it is clear that the purely instrumental theory would be saved. We should perceive something different in each position, but then the real object would have changed. This would be a very reasonable view to take if we happened to be alone in the universe, but it will not do in view of the fact that there are other people who claim to perceive the same reality as ourselves. For if what both of us perceive is a reality, and if it really alters when we move, then, if I move and the other man stands still, the same reality will both change and remain unchanged. Thus the main reason why we cannot accept this explanation is not that there is anything intrinsically improbable in it, and not that it would not perfectly well account for the changes of the objects perceived with change of position for each one of us taken separately. The trouble about it is that it will not allow us in any sense to say that two people 'perceive the same thing at the same time' no matter how much alike the objects of their perceptions may be. For the theory in question will make the objects of all the successive perceptions of each of us real, and, since the above considerations show that they cannot in general be the same realities as other people perceive at the same moment, we shall need as many realities as there are people. And this common-sense wishes to avoid.

    The suggestion then that the real actually does alter in shape as we move about will not help us greatly, and, having mentioned and discussed this suggestion, we can return with a good conscience to the problem of how much, if any, of the instrumental theory of perception can be kept when once some of it begins to be rejected. So far we have seen that no reason has been adduced even by those who say that we never can see the true shapes of solid objects, to prove that we are not right in ascribing primary qualities to the real even if perception does not at once tell us what the particular primary qualities may be. The next point to notice is that science does not believe that in no case do we perceive the real primary qualities of objects. For it holds that in the case of two-dimensional ones at any rate there are positions from which the true shape can be seen.

    Let us consider then whether there is any reasonable ground for distinguishing those cases in which we are said to perceive the true shapes of bodies from those much more numerous ones where this is denied. We will take the circle and the ellipses. All the ellipses are said to be appearances and the circle alone is said to be real. Are there any really relevant differences between the circle and the ellipses that will justify this distinction? The facts of the case here are that (a) in one set of positions and in one set alone we perceive a circle, and (b) in all positions, whatever we may see, we feel a circle. Now we have already argued in our second chapter that, apart from some kind of causal theory, it is a sheer fallacy to suppose that the agreement of two senses increases the probability that in which they agree is real. We are no more certain that what we feel is circular than that what we see is elliptical at the same moment; -- we could not be more certain, for both judgments have the greatest certainty that it is possible for judgments to have. Hence it is perfectly open to us to say either that both the seen ellipses and the felt circle are real and coexist; or that both are mere appearances; or that one is real and the other an appearance; but, so far as I know, there is no reason why what is perceived by two senses should be more likely to continue to exist when it is perceived by neither than what is perceived by only one. This was the conclusion that we reached before we elaborated the instrumental view of perception as we have been trying to do in this chapter. The question now is whether that view adds anything to the results of our earlier discussion. I am inclined to think that it does. We must remember that we are now accepting the possibility of the instrumental view -- which has never I think been successfully denied -- and that it is our present business to see if there be any ground for retaining it at all when it has been restricted as much as science and common-sense restrict it. Now, on that view, if we ever do perceive a real object, our minds are brought into direct relation with that reality owing to events that occur in it, and the possession by our minds of proper instruments. Now it is quite certain that the same real object cannot be at once circular and elliptical. Hence if our minds are ever brought at the same time into the relation of perception to an object that is at once circular and elliptical it cannot be real. Hence if we suppose that the tactual and visual shapes belong to the same object, none but the circular object can be real; for in all other cases there is this synthetic incompatibility. Thus, whilst it is perfectly true to hold as we did in an earlier chapter that agreement between the deliveries of various senses is no proof that the object is more than an appearance, yet we can say that if the mind ever comes into perceptual contact with the same reality through two different senses it is only where their deliveries agree that this can actually be the case. When there is disagreement either one sense is not in contact with reality at all, or they are not in contact with the same reality. We have already discussed in the second chapter in what sense we believe that visual and tactual spatial characteristics do belong to the same object and can be synthetically incompatible.

    I think then that the position which common-sense takes up as regards the ellipses and the circle is a perfectly reasonable one. The agreement of the senses does not indeed, as we have seen, refute the possibility that the felt and seen circle may both be appearances. If we decide then

1. that most of the visually perceived objects are to be counted as appearances so as to prevent the infinite multiplication of realities,
2. that all the visual objects and also the tactual objects are connected with a single reality, and
3. that under suitable circumstances this common reality can be an object of both sight and touch, we shall have to conclude that the reality is circular and not elliptical.

To take any of the ellipses as real, together with assumptions (a) and (b), is (1) arbitrary, since it is only the circle that is marked out by a special property, viz. the agreement of the senses, and (2) involves the view that touch does not here bring you into contact with reality at all, though sight does.

    But once the distinction has been made the laws that we can discover to connect the objects of our perceptions as regards spatial qualities will in certain knowable cases be laws connecting realities with appearances. For instance, when we have distinguished the circle as real from the ellipses as appearances, the observations that we can make on the perceptions that we have when we stand in certain places, will teach us laws connecting real primary qualities with those of appearances. And when these laws are once firmly established we shall be able to argue from an object of perception to the most probable particular primary qualities of the reality that 'corresponds' to it.

    Now our ability to do this was precisely the paradox which was so troublesome before, viz. the question of how it can be possible, for instance, to say that we know that all our spatial perceptions have merely apparent objects if these be solids. We can now easily justify this apparently paradoxical statement. We have no reason to doubt now that we can perceive the real figures that exist in two dimensions and distinguish them from mere appearances. By so doing we can discover the laws that connect the shapes of appearances seen from certain positions with the shapes of realities. Then we can give a meaning to the saying that we know that we can never see what is really a sphere. This means that when we feel a sphere we always see some kind of ellipsoid no matter in what position we stand, and when we see a sphere from some definite position, we can always only feel an ellipsoid. And the general laws that we have discovered by the consideration of the changes of shape of two- dimensional objects with changes of position will enable us to understand why this should be the case.

    So far so good then. It was essential to the scientific theory to be able to keep the instrumental view of perception with regard to primary qualities, and there seemed to be a grave doubt whether it could do this in view of the fact that for all secondaries and for many primaries, it held a different theory which made them appearances. We saw that in regard to secondaries there just was no conclusive ground for a distinction, though it would not make any real difference to the scientific theory whether it dropped them or kept them. And, with regard to the changing shapes of what we see most of which science pronounces to be appearances more or less like the reality, we saw that

1. this distinction might be drawn without our having to deny that shape and size are qualities of the real;
2. that it is possible to agree that if the instrumental theory be ever valid, it will be so only when science holds it to be so, and not when it denies that it is; and
3. that by applying this criterion and starting from the perception of objects of two dimensions, science can discover laws connecting real shapes with those of appearances seen under definite conditions, and come to the conclusion that we never see solid bodies as they really are.

    But we are by no means at the end of our troubles yet. All that has been said in the last paragraph will hold if we have reason to believe that the instrumental theory is a true account of perception in at least some cases. But the question is whether there are not other considerations beside those that have already been considered that render this very improbable. In fact the question will be: Can we give any reasonable account of what we mean by the instrument being wrongly adjusted or out of order; and will not the account that we have to give of this be so general that it will replace the old instrumental theory altogether?

    Let me now try to make the problem a little plainer. The difficulty arose most clearly over what common-sense holds to be sheer illusion, though it will be easy to see that it also applies to the case of the appearances that are called 'appearances of' a reality like them such as the successive ellipses. The position is as follows. Grant that there is illusion whether small or great and you must grant that the complex mechanism involved in perception can produce two entirely different results. Entirely different in one sense and yet on the other hand unfortunately very much alike. It is the combination of their extreme likeness and their utter difference that threatens to wreck the instrumental theory, and with it, the science of physics as ordinarily understood. When we perceive reality, if we ever do so, the effect of the whole process in the reality, the organ, the brain, and the mind is to establish a relation between the mind and the reality that we perceive. When we perceive appearance, the effect of much the same process in the organs and the brain is to produce, not a relation to something already existing, but a whole of object + relation to mind. Now two effects could hardly be more unlike than this. Yet on the other hand there is an immense likeness between them. The perceived object in both cases is very much the same. The ellipses that are only produced as elements in the whole called a perception are extremely like the circle which is believed to be able to exist out of the perception. Hence it is not unreasonable to say to the person who wants to keep the instrumental view in one place and to drop it in another: Can you really believe that practically the same mechanism can produce such utterly different results? Again, you have granted that most of the objects that you perceive are appearances. You only see the circle which you believe to be real in one set of positions; but you see the ellipses which you believe to be appearances from an infinite number of sets of positions. Surely it would be more reasonable to hold that it too is an appearance. Look at the advantages that will accrue from this slight change. At once you will be able to drop this incredible belief that the same mechanism sometimes brings your mind into relation with a previously existing object and sometimes creates the object in the relation. And, with the dropping of the difference, the likeness which was so puzzling on your original theory will become natural. In all cases the effect will be the production of a perception as a whole whose object cannot continue to exist out of it. What then more likely than that some common cause under slightly varying conditions produces these very similar perceptions?

    This is the argument for idealism as against the instrumental theory of knowledge when an effort is made to confine the latter to some parts only of perception. It offers common-sense and science a choice between the incredible view which they agree in rejecting that anything that anybody perceives anywhere is real and the view which it has just attacked. It concludes that realism can keep to neither position and must pass over into complete idealism. The argument seems to me to be a powerful one, but the results of accepting it are serious. All that we can perceive is appearance, and there is no reason to suppose that the real has any qualities like those which we perceive. All that can be said of the real is that it must be of such a nature as to be able to cause the perceptions that people actually have.

    We must consider this argument as carefully as possible and see if it be sound. The line that it takes is that we must suppose that in many cases the effect of the processes in our organs and brains is to set up a perception as a whole instead of a relation to a real object, and that therefore it is better to assume that this is what happens in all cases of perception. In fact the present position is that the causation of our perceptions can be analysed vertically into states of brain, caused by states of organs, caused by states of something else. The states of brain, however caused, produce the same perception whose object is of course an appearance; but in some cases the object perceived resembles a reality, states in which are a remote cause of those in the organ.

    The first question is whether this view can formulate its position consistently with its own conclusions. We must remember that we are still left with all the old observations, viz. those that tell us that without an eye colours are not perceived, and with an eye the possibility of perceiving various colours depends on the internal structure of the eye. But, whilst it was easy to formulate these conclusions on the instrumental theory, it is less so now that we believe that all objects of perception, and therefore the eye and its structure, are appearances. I think however it can be done. I know that when it is impossible for me to perceive an eye in a man's body under circumstances where I might expect to do so, that as a rule he cannot perceive colours or visual extension. On the causal theory the ultimate cause of my perceiving an eye is certain states of my brain. A remoter cause is states of my own eye, and a still remoter one is some other states of the real. Now it is clear that by all these conditions I do not mean perceived conditions. For it is certain that people perceive colours when no one perceives their eyes or their brains. Hence we must put the whole theory into terms of real causes of perception. I think it will then become reasonable to state the observed facts in the following way: There is a relatively permanent structure in reality, which is a condition of the possibility of the mind which is connected with it, perceiving coloured and extended appearances, and which is also a remote cause of other people, whose minds are possessed of similar real structures, perceiving an eye. We can deal in the same way with correlations between the perceptible structure of an organ and the possibility of perceiving some particular quality like red or green.

    Thus it is hardly true to say that a purely causal theory leads to complete agnosticism, for it does allow of a certain amount of analysis of the causes of our perception in accordance with the actually observed conditions for their production. We must now see whether such an analysis cannot be carried further. If we consider the general nature of what we perceive we shall see that all perceptions have much in common. They are all built up out of quite a few general qualities like colour, sound, extension, figure, taste, smell, temperature, etc., which continually recur. The differences other than geometrical between our objects of perception consist in the following respects: (1) The presence of a given general quality in one and its total absence in another; (2) Difference in the degrees of the characteristics of the qualities. By this I mean that the general qualities like colour have for their particularisation a small number of characteristics which may be compared to independent variables -- e.g. colour is particularised by colour-tone, saturation, and intensity. Each of these variables has a continuous set of values, and perceptions differ in their objects according as the values of these variables differ. Apart from characteristics and their continuous series of possible values there would be only 2ⁿ-1 different possible objects of perception where n is the number of different general qualities and is, as we have seen, quite a small number. But all these general qualities have to be particularised by the special values of their characteristics. Of these they generally possess several -- thus colour and sound have three apiece -- and each of them is generally supposed to have a continuous or at any rate a compact series of possible values. It is from the last fact that the infinite variety of the objects that we perceive springs.

    Now this analysis of what we do perceive at once suggests, it seems to me, a further analysis of the causes of our perceptions. We have now seen that we have very good evidence for the belief that the possibility of having perceptions, whose objects have the general qualities that we have mentioned, depends on the connexion of the mind with a real structure, states of which are the condition of one mind perceiving these general qualities, and other states of which are the cause of other minds connected with similar structures perceiving bodily organs. Hence the general qualities perceived can be correlated with this permanent real structure without which they cannot be perceived.

    But, on the other band, we are not able to perceive in our organs anything that corresponds to the particular values of the characteristics of these general qualities, which perpetually alter as we have different perceptions. But it seems not unreasonable to believe that what determines the perception of a given particular quality at a certain moment must be states in that permanent structure which we believe to be the condition for the perception of the general quality of which this is one possible particularisation. This, at any rate, seems the most reasonable analysis to make.

    We must not, however, make the mistake of supposing that we can go on to conclude that if a particular quality has (say) three independent characteristics, there must be either three real states in its cause or that, if there be only one state it must have three distinguishable characteristics like e.g. wave-length, amplitude, and form. For we saw in the chapter on Causality that, although a different effect -- however small the difference -- must have a different cause, yet this does not prove that, when the differences in the effects are differences in the values of certain independent variables with a continuous range of values, the cause of any given effect of the kind must be as differentiated as that effect. We cannot, in fact, be sure that the three characteristics of perceived colours may not be due to events that have only one variable characteristic.

    I think we can now say that we have been able to show that a purely causal theory, which makes all the objects of perception appearances, can be stated compatibly with the observations about our bodily organs with which the two rival views of instrument and cause both started. We have seen what sort of analysis can probably be made, on the strength of those observations, of the unknown causes of our perceptions. But the difficulties attending the scientific theory of the causation of perceptions on this view, which makes the objects of all our perceptions appearances, remains untouched. What is the objection to the scientific theory from our standpoint? It is a theory of the more remote causes of our perceptions, of the causes of those states in our organs and minds, which, however caused, end in a perception of an appearance. But it is stated in terms of primary qualities and it actually involves the view that we can find out the primary qualities of these remote causes in many cases from those of the appearance perceived. Hence it assumes that the remote causes of our perceptions resemble their objects not only in the general way that both have primary qualities, but also in the much more particular one that there is a general resemblance between the shape of the appearance and the shape of the remote cause. We might put the matter thus: Real primary qualities are essential to the scientific theory, therefore (a) the causes of our perceptions are held to have primary qualities and must be real, since they are admitted to be imperceptible, and (b) the theory can only be built up by assuming that the causal laws between these remote causes and the events in the real structure of our organs are those that hold between observable primary qualities. On the other hand the conclusion of the theory gives us no warrant whatever for supposing that primary qualities are any more than appearances. And finally it seems a very extraordinary thing that science should hold that what resembles the object that we perceive is not its immediate cause, or the last cause but one, but a cause which, on its own theory, is a long way back in the vertical causal series.

    The first point that we have to notice is that science holds that in general we only perceive an object which something in the real resembles, when other people also perceive it or can do so. There are difficulties about this view which we will discuss later; at present we will accept it. Now we notice that under similar circumstances a slight change in our own position, when we remain as we say, 'looking at the same thing,' makes but a very slight change in the qualities of what we perceive. The ellipses are very like the circle and each other. Now this I think quite reasonably suggests that under such circumstances our perceptions have a common remote cause, and that some slight change of condition makes the difference in what we perceive. This is the sort of justification that science can offer for the apparently arbitrary procedure of fleeing to a remote member of the causal series as the one that is supposed to resemble the object perceived. It does not of course justify the assertion that the object perceived is like any of the causes of the perception ; but it does suggest that, if it were, it would be a cause remote enough to be common to the causal series of several observers that it would resemble.

    The next point on which we must be clear is that the further determination of the real world does not pretend to be anything more than hypothetical. This, it must be remembered, would be true of such arguments and conclusions as are involved in the wave- theory of light and the dynamical theory of gases even if we could have maintained the instrumental theory, and held that we sometimes perceived the real. For, although on that theory we perceive the real, it is quite certain that we do not perceive those particular realities with which the scientific theory deals, and therefore they can only be proved by the success with which they account for what we can perceive. Now, the only reason that we are worse off when we believe that we do not perceive the real is that the initial probability of an hypothesis about the real, stated in terms of qualities of what we perceive, is less. The probability that is reflected back on such an hypothesis by the fact that it does explain what we perceive remains the same as before. But it is easy to see that, under the circumstances, any alternative hypothesis about the real will have to rest its probability entirely on its ability to explain the perceived. For by our own admission nothing is directly known about the qualities of the real and therefore the initial probability of any further particular determination of it is the same as that of any other, so long as the laws of logic and probability are obeyed by it. Hence in comparing the probability of any two alternative theories as to the further determination of the nature of the real causes of perception we need not consider anything but their respective success in explaining what we do perceive. And there is certainly no alternative theory of the nature of the real before the public at present that can claim to explain so many of the facts so well as the theory of science. Thus the correct answer of science to such an objection as Dr McTaggart makes in his Dogmas of Religion, that 'the existence of matter is a bare possibility to which it would be foolish to attach the least importance⁵,' is that, whilst all alternative possibilities are equally bare when you start from the view that what you actually perceive is appearance, this particular one accounts for the perceptions that we actually do have in a way in which no other, so far as we can tell, does. (I have already discussed in my chapter on Phenomenalism the plausible theory that the causes of our perceptions are themselves mental in character.)

    But the statement that, on the theory of probability, if we start from the view that all that we perceive is appearance, the further determination of reality in terms of primary qualities which science offers is the most probable with which we are acquainted, must not be misunderstood. Science has absolutely no need to suppose that reality has those peculiarities which I have already mentioned as being incommunicable even from man to man. I mean the peculiar and incommunicable sense experiences that we have. It is true that we cannot perceive reality and therefore when we say that there is a real square we cannot mean that the reality has that sensuous particularity that we experience when we see a square. But this is utterly unimportant to science, because, as we have seen, such sensuous particularity is absolutely incommunicable, and therefore cannot be a possible subject of a science of any kind. Just as we cannot possibly know whether A and B, who always use the words 'red' and 'green' under the same circumstances, really have the same experience, so we cannot and do not need to know whether the real has the peculiar sensuous quality that we experience when we use those terms. But just as we can agree with each other as to the use of these terms -- the important point being that we all find and fail to find distinctions in what we perceive in agreement with each other -- so we can ascribe primary qualities to reality in the sense that we can believe that it will agree in having distinctions where we perceive spatial distinctions and where other people agree with us in perceiving them. This, then, is all that can be demanded when we say that the real has primary qualities; we cannot mean more than when we say that the objects of other people's perceptions can be known to be square or red, and we know that this merely means that one of us will never find homogeneity where the other finds distinction.

    If, then, we allow science to assume hypothetically the reality of at least some primary qualities, we have seen that it can build up a very successful theory to account for the perception both of primaries and of secondaries. It does this, as we saw, by assuming that the real shapes are those for which sight and touch agree, and therefore that in some cases at least, though very few, the appearance is exactly like the reality events in which are a remote cause of our perception, whilst in general the perceived distance of a visible object is the real distance of the remote cause. But it would obviously be very much better if the scientific theory could be stated in a much less definite form. If, in fact, we could state it in terms of causes without having to specify their nature so accurately, it is clear that it would still retain such probability as it does from explaining the facts, but would gain in probability by not having to make such definite and complicated assumptions about reality. The question is whether this is possible, and to this question we now turn.

    It is tolerably easy to offer an account of the scientific theory of the causation of our perceptions of sounds which does not assume the reality of primary qualities. The ordinary arguments assume this reality and proceed from the fact that when we begin to hear a sound there is strong reason to believe that we could always have perceived a body vibrating which began to vibrate at a time before we began to hear the sound. This time is shown to depend on the perceived distance of the vibrating body and the nature of the medium between it and our ears. Now, on the present theory, to say that we always could have perceived a body vibrating at a certain time, means that a real thing existed, states in which are capable of making us perceive such a body. We know that there must be such real causes on the present theory; we know, too, that they are remote causes, events in which produce real changes in that real structure which 'corresponds' in the sense discussed earlier to our perceptible ears. But we do not need for the present purpose further to specify the nature of that real thing. Hence we can state the scientific law as follows: A remote cause of our hearing a sound is a remote cause, events in which are capable of making us perceive a vibrating body if there be a proper organ in a proper state at the time. Thus the theory adopted by science for the cause of our perception of sounds, though stated in terms of primary qualities, can be stated just as well in terms of the supposed remote causes of our perceptions of primary qualities. It then becomes indifferent to us whether primary qualities be realities or merely appearances, and science does no harm in continuing to state its position in terms of primaries, since we can always interpret it in the way in which we have just been doing.

    But clearly this will not help us very far unless we can also state the scientific theory of the causation of our perceptions of primary qualities, and of colours in terms that do not assume the reality of primaries. And this is by no means a simple problem.

    Let us begin by stating the scientific theory in terms of primaries, and then see if it be possible to transform it. The theory is that the last cause of our perceiving an object of a definite shape and colour is states in our brains; that the cause of these is states in our eyes; that the cause of these is vibrations that travel with a definite velocity through an imperceptible medium; and that the cause of these is the vibrations of numbers of imperceptible particles. This last stage of the causal process is supposed to have a definite figure closely related to that which we perceive as a result of the whole process. Moreover, the little particles, beside lying within this definite boundary, are supposed to have a position in space relatively to us, which is practically that in which the perceived figure is seen to be. Consider now for a moment the difficulties that beset any attempt to state such a theory as this in terms which do not involve the reality of primary qualities. There are three difficulties about this theory over and above those which occur in the physical account of the perception of sounds. (1) With sound we could under favourable circumstances perceive the vibrating body and the medium. Here we cannot even theoretically perceive either the particles or the medium or their motions. (2) The theory of sound does not try to explain the causation of our perceptions of sounds which it grants to be appearances by the states of supposed real sounds. But this theory does undertake to explain the perception of primary qualities by real primary qualities and their states, whilst it is forced to conclude that, so far as we can tell, there is every probability that all the primary qualities that we perceive are appearances. (3) As a consequence of this difference the theory of sound did not have to come to the amazing conclusion that a cause four stages back in the process closely resembles the object of the perception, which the subsequent stages end by producing. But this is the conclusion at which the theory of light arrives, or, perhaps we ought to say, from which it starts. Now these three difficulties, peculiar to the theory of light, end in another paradox, which seems almost insoluble except on the assumption of the reality of primary qualities. Science tells us that the remote cause of our perception of an object is imperceptible parts of that object. But it also holds that the object perceived is an appearance; for we perceive chairs and tables as homogeneous and not as quantities of little bodies in rapid motion. But it is hard to see how a reality can be part of an appearance, even if we grant that these can be unperceived parts of an appearance at all. The solution of the paradox seems to depend entirely on the assumption, not merely that primary qualities are real, but also that, as far as distance and shape are concerned, the primary qualities of the appearance that we perceive are substantially similar to those of its remote cause. It then can be said that the little particles are unperceived, and that they form part of a reality which occupies practically the same place as the perceived appearance. But this solution does not seem possible without these very special, and, so far as I know, intrinsically groundless assumptions.

    We must not however despair, but see if we cannot state the essence of the scientific theory of the perception of primaries without assuming their reality. We have already seen that the fact that all persons under certain circumstances perceive much the same objects -- e.g. ellipses -- renders it very probable that there is a common remote cause of their perceptions. Let us revert, then, to the case of the circle and the ellipses. We know that in whatever position we may be, so long as we touch the object, we feel something circular. The question of whether we touch it or not depends on our own volitions. Thus we seem to be justified on the causal theory in supposing that there is a permanent reality which, whenever we will, will give us the same tactual sensations of shape. We know further that we can often get these tactual sensations when we cannot see anything at all. This suggests that the cause of our seeing the circular or elliptical object, when we do see it, is events that do not always take place. 'In the dark,' as we put it, these events are presumably not taking place. But when they do happen we perceive an object that is geometrically very much like what we feel, and, under certain circumstances, is exactly like it as far as shape is concerned. Now this, I think, suggests that there is some permanent reality which causes our sensations of touch whenever we will, and that sometimes events happen in that reality which cause us to see objects of various shapes which, however, are always like the felt shape.

    Now the question is whether we might not be allowed to assume the instrumental theory for touch even though we have had to drop it for sight. Let us recall for a moment why it seemed unlikely to be true for sight, and see whether the same argument will apply to touch or not. There was nothing intrinsically impossible or even improbable about the instrumental theory to begin with. It remained a perfectly possible alternative theory to the causal one, which makes all our perceptions appearances until we come to the fact that science and common-sense agree in believing that the greater part of our visual perceptions, even of primary qualities, are mere appearances. Then it had to hold that precisely the same sort of causal processes in the same bodily organs must be capable of producing two entirely different results, viz. the establishment of a relation between the mind and a reality, and the production of a whole perception consisting of an apparent object very like the one that is supposed to be real + the same sort of relation to the mind as we had before. And we agreed that this was a very unlikely state of affairs, and that it seemed much more reasonable to suppose that in all cases the effect was of the same nature, viz. the production of the perception of an appearance as a whole. Thus the ground of the decision against the instrumental theory in the case of sight was that it was held that most of the objects perceived by sight were appearances. But this conclusion does not prejudice the possibility of the instrumental theory for other organs of perception. If with them, e.g. with touch, we were to find no reason for supposing that any of the objects perceived were appearances, we should no longer have the paradox of the same causal process producing two utterly different effects, and therefore no ground for rejecting the instrumental theory as regards the deliveries of that organ.

    Now it is at least obvious on the face of it that there are very much fewer cases of perception of objects by touch that are declared to be illusory than there are of sight. For instance, all the difficulties that arise from change of shape with change of position vanish at once here. So long as we feel the object at all, no matter who we are or where we are, we feel the same shape, or at worst can explain the change of shape by a real change in the object. Our feeling it or not depends on our volition, but when we once feel it we always feel it as having the same shape.

    But it will be said: There are illusions of touch, and even though there be much fewer than of sight, that is enough to wreck the theory that the organs of touch act purely instrumentally. Let us then consider these supposed illusions and see whether they be really relevant. The two following seem to be typical cases. (i) There is the old Aristotelian experiment of holding a pen between the crossed first and second fingers so that it touches the back of the former and the inside of the latter. Under these circumstances it is said that two pens are felt instead of one. (I cannot get the illusion myself, but I am prepared to believe Aristotle and the numerous other distinguished persons who have been more fortunate than I have.) (ii) The other is the illusion that has been pretty closely investigated in modern times -- of the two compass points which have to be placed at different distances apart when applied to different parts of the skin in order to be felt as distinct. Everyone is acquainted with a particular application of this who has been so unfortunate as to have a hole in his tooth. This will appear enormous to his tongue and tiny to the eyes of himself and his dentist.

    I do not think either of these criticisms need prevent us from holding that touch is a sense that acts purely instrumentally, and that for aught we know to the contrary, tells us the real shapes of real things. In the first place, so far as I know, there are not supposed to be any illusions about felt shape. The two illusions mentioned above rest on the fact that a judgment in the one case about number and in the other about distance and length, conflict with judgments based on the deliveries of sight; and in these cases we accept sight. The first point to notice is that the experiment with the compass points is entirely irrelevant to the possibility of the instrumental theory. It does not make against that theory if the use of the instrument does not tell you the whole truth about the real; the troubles arise when it gives you a perception with an object that is believed to be an appearance. Now, if there be really two compass-points, and under certain circumstances you only feel one, there is no apparent object involved, and therefore no argument against the instrumental theory. You explain the facts at once by saying that the skin on your back is not nearly such a delicate instrument for perceiving the real as is the skin on your tongue-tip, and therefore distinctions in the real can be discovered by one which are left unnoticed when the other is employed. And if you pass to the further experiment by which it is found that at different parts of the skin, when the compass-points are far enough apart to be distinctly perceived in all cases, the distances perceived by the eye and the skin do not agree, this still is not relevant.

    We do not here have at some points, or at all, illusory objects of perception. At all the points we perceive distances between the two compass-needles, but when we compare their magnitude that at one point seems greater than that at another, although we do Dot believe that this is really true. Now, comparison of a past perception with a present one in respect of the magnitude of one of its characteristics is quite clearly an act of judgment and not of perception. Now there is no reason on a purely instrumental theory why you should not make erroneous judgments about the real. Let us be quite clear about this point. When I have a perception on any theory, certain of the judgments that I make about its object must be infallible, e.g. judgments as to its being extended, and having such and such a colour or shape. Now, whilst the judgment that it has extensive magnitude and that its boundary lines have length, is infallible, it is quite clear that the perception does not guarantee infallible judgments as to what those lengths are. For you could at best only have infallible judgments as to one length being greater than, equal to, or less than another in the same object of perception. Now it is clear that the present experiment with compass-points does not make us suppose on the instrumental theory that now one of two lines in the real is longer and now shorter than the other. It only tells us at best that if we can trust our memories it seems likely that the length that we now perceive would be judged to be greater than the one that we perceived when a different part of the akin was touched, if as a matter of fact both lengths could be perceived at once, which they cannot. But when once we grant that there is no question in either case of a positive perception of something that is believed to be an appearance, but merely the question of a judgment of comparison between a characteristic in an object perceived by two different instruments we have no difficulty in accounting for the facts compatibly with the instrumental theory that in both cases what we perceive is the real object. Judgments of comparison between the object of two different perceptions may very well be determined by other causes besides what is actually perceived. We may perceive real distance and perceive it as having a definite magnitude, but the actual magnitude which we judge it to have may well depend on other circumstances beside the perceived distance. Hence the same distance may well be judged to have different magnitudes when perceived by different instruments. Nor indeed have we far to seek for the cause of our judging that the magnitude differs in the two cases. In both cases the instruments used are parts of the skin. We know from the earlier forms of this experiment, which I have already discussed, that some parts of the skin are more delicate instruments than others in that one part can discover distinctions when the other only finds homogeneity. Hence it is clear that in the less sensitive parts of the skin, when the distance is really the same, the real state of affairs will be more like that in which no distinction can be detected than it is at a more sensitive part. And this may well be interpreted as a real shortening of the distance between the points. Thus I think that we are justified in holding that, as far as the compass-point experiment is concerned, there is no reason for supposing that what we perceive by the sense of touch is ever an appearance, at least as regards geometrical qualities. And this leaves it perfectly open to us to assume the instrumental theory for this sense. We have not indeed disproved the causal theory which makes the objects of all our perceptions appearances, but it removes the sole ground which led us to prefer that view in the case of sight. The causal theory for touch remains a possibility which it would be foolish to adopt without necessity, since with the instrumental alternative we can accept substantially the theories of physics, whilst with the causal one it is doubtful if we could transform them so that the same evidence still supported them.

    It now remains to say a word about Aristotle's experiment, and to show that this, too, is erroneous judgment, and not the perception of an appearance, as is the seeing of ellipses when what is real is a circle. The first point to notice is that two instruments of perception are used on the instrumental theory -- the outer part of one and the inner part of the other finger. The second point is that if the deliveries of the sense of touch can be trusted, which of course on the instrumental theory they can be, these two organs are not in contact with the same part of the reality. These two facts, which are true on the instrumental theory, can now be used to explain the illusion compatibly with it. No one in the position in which the fingers are held ever does have a perception of a single round surface. He feels, on the contrary, two bits of round surfaces. But the assertion that we perceive a pen means that we perceive the whole circular surface, and this we do not do. Hence under the circumstances any assertion about pens, and therefore about the number of pens, is not a judgment based entirely on a perception and guaranteed by it, but is either an inference or an association. It is as much an inference to say, under the conditions of the experiment, that you hold one pen as that you hold two; the only difference is that the latter inference is liable to be made and that it happens to be erroneous. Thus we do not perceive an appearance, but we make a false judgment. And so this attempt to show that we sometimes perceive appearances by means of touch seems to have broken down.

    Touch, then, we may conclude, for anything that we have yet learnt, is a purely instrumental sense which always makes us perceive the truth about the geometrical qualities of real objects, even if it be only a small part of the truth and if we be liable to base unwarrantable inferences on such partial knowledge. But if once this position be granted, we have made an immense step forward in the rehabilitation of the scientific theory of the causation of visual perceptions. For we can now agree with science that the geometrical qualities of the appearances that we see bear a close resemblance to those of certain reals, and that in some cases they are exactly like them. And science will now be justified, if it finds that view conducive to the explanation of our visual perceptions -- as it does, in supposing that a remote cause of its perceptions is in many cases events which are imperceptible in these tangible reals that resemble the objects of visual perception. For the recognition of the reality of the tangible carries with it a solution of the paradoxes mentioned on p. 252. For instance, there is now no difficulty about real, but imperceptible events in imperceptible little bodies which occupy the same place as that in which the body is perceived to be. For it was granted that touch did not tell us the whole truth about tangible realities. But it was claimed that it told us, so far as we know, nothing but the truth about their geometrical qualities. In that case they are truly extended, and may well have parts too small for our senses to perceive. Again, it now ceases to be arbitrary to take the fourth stage backwards in the causation of a visual perception for that which 'corresponds' to the object perceived. For now we have reason to believe that there can be reals which closely resemble the object perceived in shape, and that events in them may be the common cause of similar but slightly different visual perceptions in various people. It is clearly not arbitrary to take as the corresponding reality that which resembles in geometric form these perceptions' objects, and is at the same time the common remote cause of the perceptions.

    At the same time I should hesitate to lay too much stress on the instrumental character of touch. It is evident that in order to be able to maintain it we must be prepared to assert that we never perceive appearances by touch, at any rate, as regards figure. We must be able to prove of any suggested case that it is either a perception of fewer, but not of different distinctions from those of the real, or that it is not a case of perception of appearance, but of erroneous judgment based on the perception of the real. Now it would certainly be rash to maintain that no cases do arise which are only explicable as perceptions of appearances. If, for example, we ever have tactual experiences in dreams it is doubtful whether they could be explained otherwise than as the perceptions of appearances. I do not know that we ever do feel the shapes of things in dreams, but a theory that rested on the assumption that we never do so would be in a precarious state.

    Fortunately, however, by combining the facts of sight and touch it is possible, even on the assumption that the causal theory holds for the latter sense as well as for the former, to gain some probable conclusions about the real causes of our perceptions of appearances. It is granted that the approximate agreement of our visual perceptions under given circumstances suggests a common remote cause for them. Further, the fact that practically always we all feel the same shape under these circumstances if we will move our fingers along the edges, makes it almost certain that there is a common remote cause of our perceptions of tactual figure. And this is found to be independent of the relative position of the object touched and the body of the person who touches it other than the actual touching organ. Again, there is always a general agreement in shape under these circumstances between what we feel and what we see, and under some circumstances a complete agreement. Yet the processes of causation of the two sorts of perception are widely different. They employ different organs, and one set of perceptions can be had in the absence of the other. Now the fact that when we feel an object we can nearly always see an object of much the same shape tends, I think, to show that there is probably a common set of conditions which the causes of the two kinds of perception obey. When we add to this the facts that there is every reason to believe that the intermediate stages in the causal process are widely different in the two cases, and that something that we have previously only felt may subsequently be accompanied by a visual appearance (owing, e.g., to its being heated or illuminated), we shall be inclined to believe that the supposed identity of conditions in the remote causes of our corresponding perceptions of sight and touch are not identical events. If, then, the events differ, as they must do, since the intermediate causation is so different, and since one sort of perception can be had without the other, we must look for the identity which is to explain why, when both sorts of perceptions do occur together, their shapes do so closely correspond in something else than remote events. It looks, in fact, as if we might find it in some permanent conditions of relations, which both the events that cause the visual perceptions and those that cause the corresponding tactual ones obey. Now it seems to me that the simplest way to account for all these facts is to assume a real counterpart to tactual perceptions whenever we can share those perceptions with others, and so have reasons to believe that they are due to a common remote cause.

    Let us recapitulate the advantages that such an assumption offers us.

1. We have already seen that we practically never suppose that tactual perception deceives us as to the shape of the real. So much was this so that, except for the fact that cases might possibly arise in which we should have to flee to appearances of touch, we urged that there was no reason to deny the possibility that tactual objects of perception were real. If we think, however, that it is safer to believe that tactual objects, too, are appearances, they will have the advantage over visual appearances that, whereas the assumption that the former were all real would lead to terrible complications, no such complications would arise over the belief that tactual appearances were real. Now this is essential to the theory of a real spatial counterpart. To make this the counterpart of visually perceived spatial appearances would make the world of reality as complicated as it would be if we supposed that these visual appearances were themselves real. But to make it a counterpart of the tactual appearances will not lead to these complications because we already know that there is only one tactual appearance to an infinite number of corresponding visual ones. Hence the internal consistency and the comparative simplicity of tactual appearances make it reasonable to hold that, if there be a spatial counterpart at all, it will be to tactual and not to visual spatial appearances.
2. The assumption of such a counterpart avoids the assumption either that what we perceive is more than appearance, or that the reality that causes the perception is exactly like the object of the latter. It avoids the belief which we have already seen to be strictly impossible of proof, or even of conjecture, that the real remote causes of our perceptions have the same sort of sensuous particularity as do the objects of each man's perceptions for himself. But it replaces it by the belief that there is a one to one correspondence between perceived geometrical distinctions in the object of tactual perception and certain permanent ones in the reality events in which cause the perception. And this is all that we mean when we say that another man perceives the same object as we do.
3. It offers an explanation of the facts (a) that the shapes of visual appearances and of tactual ones are always correlated closely and may be identical, although the perceptions of which they form an analysable element must be very differently caused; and (b) that the tactual perceptions of different people agree, whilst their visual perceptions under such circumstances only differ slightly.
4. It thus enables the ordinary scientific theory of visual perception and its causes to be built up on the foundation of the essential reality of the shapes given in tactual perception. For it is to these shapes that there is a real one to one correspondence. The theory of a real counterpart to tactual appearances thus gains any probability that the success of the scientific theory of perception is able to reflect on its premises, and this is of course a very great deal.
5. On the other hand it is not tied down like the instrumental theory to accept every tactual perception that occurs as supplying true information about the spatial relations of the real. All the objects of tactual perception for it are appearances. To nearly all of them it is able to believe that there are real counterparts. On this assumption it builds up the scientific view of the world and in particular of visual perception into an immense self-consistent whole. If now it ever happens -- as far as I am aware it never does -- that a tactual perception occurs which leads to the belief in a 'real' shape which does not fit in with the rest of the scientific theory, and which cannot be explained away either as false judgment or merely partial perception, the present theory is prepared to meet it. It knew all along that all the objects of its tactual perceptions were appearances, but, on the assumption that to practically all of them there is a real counterpart, it has been able to build up a consistent theory of visual perception which has now attained to such probability from perpetual verification by experiment that in the case of these (possible) few objects of tactual perception it may be able to deny that there is a real counterpart to them on the ground that such a belief would be inconsistent with its whole well-verified body of knowledge.

    Our conclusion, then, is that it is most probable that there is a real counterpart corresponding point for point to what is perceived in most (perhaps in all) the tactual perceptions that we have of figure, though doubtless more differentiated than the tactual objects themselves; and that events in this reality are the causes of our visual perceptions, according to laws which science, stating its position in terms of perceptible primaries, is able to discover. Whether there be any real correlate to the particular colours that we perceive over and above the real correlates of the imperceptible motions which science demands it is impossible to tell. That the real possesses something more than the correlate of tactual extension there is no reason to doubt; for tactual extension and visual extensions are both extensions of something. But what that something is and whether it or only events in it differ when we perceive different colours, temperatures, and 'feels' it is impossible to decide. Only this much can be said, that where, as in physical optics and in the scientific theories of sound and of heat (Kinetic Theory of Gases), we can make up successful hypothetical laws of the causation of our perceptions in terms of the counterparts of figures, spatial relations, and their changes alone; the belief that there are actual correlated qualities in the real is pro tanto weakened in probability. The reality of colours, and sounds, and temperatures, or rather of a real correlate to these general qualities in the remote causes of our perceiving them is not disproved by the scientific theory; these qualities are in the same depressing logical position as Dr McTaggart's non-omnipotent and non-creative God -- 'the only reason against their reality is that there is no reason for it.' In such good company we will leave them.

    Before ending this rather tedious chapter we must, however, see how the causal theory has affected our previous position about dreams and drugs and instruments which we had to leave in a rather unsatisfactory state at the end of the third chapter. It will be remembered that in that chapter we came to the conclusion that, apart from the causal theory of perception, it was impossible to draw a distinction on any reasonable basis between the reality of the God whom the mystic can only perceive after certain definite initiatory processes, the pink rats that can only be seen by those who habitually take excess of alcohol, and the nuclei of cells which can only be seen by people who use microscopes after a certain prescribed method. We saw that the scientist wanted to put the cell-nuclei into an impregnable position, after which the Deity and the rodents must sigh in vain, and that there was grave doubt whether, even with the causal theory, he could do this. But we have travelled some distance since we left that chapter, and we may now be better able to deal with the question. The old difficulty was that it seemed monstrous to hold that the fact that mystics only experienced God, or people only saw everything yellow when they had performed certain rites or taken santonin, proved that what they saw was appearance, whilst the entirely comparable case of using a microscope did not prove any such thing. And our discussion of the instrumental view has only increased our certainty that any such arguments to prove that an object of perception is an appearance are invalid. The theory that the mystic initiation is a necessary means to the perception of a reality that cannot be perceived without it is a priori as reasonable a view as the alternative that those initiations are just the causes of the perception of appearances by the persons who employ them.

    On the other hand, the upshot of the present chapter has been to show that, unless we want to have an immense complication of similar realities that are only perceptible from one position or by one person, we must in many cases reject the instrumental theory; and that when we once begin to do this in any case there are good grounds for doing so in all cases, certainly as far as sight is concerned. Hence we have now to explain why, when it is granted that what the mystic, the drunkard, and the microscopist perceive is equally appearance, we hold that the last mentioned gives additional knowledge about reality and are doubtful whether the two former do so.

    At first sight the microscope seems to present a contradiction to the views that we have put forward as to it being reasonable to assume a real counterpart to tactual figure, but not in general to visual figure. For it almost seems as if we were here trusting our eyes as against touch for a knowledge of reality. A little consideration will prove that this is not the case and will justify the confidence that is placed in vision with a properly constructed optical instrument. If we assume that there exists as a rule a real counterpart to figures which we agree on perceiving by touch, we get the laws connecting these figures with what is perceived by sight under definite conditions as laws connecting the shapes of visual objects with the real counterparts of tactual ones. Thus are developed the theorems of geometrical optics. By applying these laws we learn that an arrangement of tangible points in a plane, if looked at through a microscope properly focussed and at right angles to that plane, will be replaced in visual perception by an object whose shape, at any rate at the centre of the field of vision, will not differ from the tangible shape, but whose size will seem greater than the tangible size. This last phrase means that the distance apart of two points seen through the microscope will be judged to be equal to a tangible length greater than that which we actually feel. Now it should be noticed that in this point, where there is a positive inconsistency between the teaching of sight as aided by the microscope and touch, we do not hold that sight is correct, but that touch is. That is, we believe that whatever corresponds to length in the real counterpart of the tactual figure agrees with it rather than with the lengths perceived by means of the microscope. But we also know that two points that may be perceived as one by the skin at one point may be perceived as two at other points. Hence it is fair to conclude that in the real counterpart when whatever corresponds to tactual distance diminishes beyond a certain amount it no longer is able to produce a tactual perception with two distinguishable points. Hence we are led to conclude that the inability to distinguish two points in our tactual perception does not prove that there is not a real distinction of the same kind as is responsible for the differences of tactual magnitude that we actually can perceive. Now we know from the general laws of light that a microscope makes two points which can be perceived tactually as distinct to be perceived as still further apart in the visual appearance, i.e. as being as far apart as two points which, seen by the naked eye, would correspond to a larger tactual distance. Hence it is reasonable to believe that in vision with a microscope really distinct points too 'near together' to produce any distinction of tactual character, are able to produce distinctions in the visual perception's object.

    It is reasonable, then, to hold that in vision with a microscope we learn about real distinctions of the same type and in the same relations as those which do produce distinctions in objects of tactual perception and of visual perception with the naked eye, but which in their real relations have less of that magnitude which accounts for the perception of length than is necessary to cause perceptions with distinctions in their objects without the use of artificial aids to perception. In this sense, then, I think the belief that properly constructed optical instruments give us information about reality subject to limitations put upon them by the theory of light is justified. And, so far from conflicting with the belief in a real counterpart to tactual objects of perception it can only be properly defended on some such assumption.

    We can therefore pass at once to the case of drugs and of drunkenness. Mach tells us in his Analysis of Sensations that if a person takes santonin everything will appear yellow to him. We may take this fact as a text for the subsequent discussion, assuming on Mach's authority that it is true. Most people would hold that the yellow colour, due to taking the drug, is a mere appearance, and even the scientist who thinks that all colours are appearances would hold that this was unreal in some special sense. A priori the following views are possible:

1. The taking of santonin is comparable with the use of a microscope. It causes the perception of an appearance with a distinction in it to which something in the reality corresponds, but which does not make itself felt in the perceptions produced in people who have not taken santonin.
2. The taking of santonin makes a real change in the real cause of the perception, so that it now causes a perception of a yellow object.
3. The drug affects the brain or other organs involved in perception and causes the same remote cause to produce a different effect.

    I think we can practically dismiss the first alternative with a very few words. If santonin made us perceive a new colour there would be much to be said for the position here taken up. It might well be explained by the fact that the taking of the drug enabled us to have perceptions corresponding to wavelengths which now produce no effect on the mind. But it is quite clear that this is not what happens. We all agree with the person who has taken the drug in perceiving objects of practically the same shape and with some colour or other. Also we agree among ourselves about the colour and unite in disagreeing with the patient. Now the complete agreement, as we have already argued, suggests a common remote cause. But the difference is not one like we have between the microscope and the naked eye, that one perceives distinctions which the other simply fails to perceive. The drugged person simply differs from everyone else in the colour that he perceives; he does not perceive a fresh distinction; in fact, if Mach be taken to mean that he perceives everything as uniformly yellow, his position as against others is that of the colour-blind man against the rest of the world, rather than that of the microscope against the naked eye. If he be right then the agreement between other people to perceive various colours becomes inexplicable.

    The second alternative cannot possibly stand by itself. If when A takes santonin changes do really take place in the remote cause of his perceptions which make it contain those events which cause the perception of yellow, you have to explain why none of the other people, all of whom are capable of perceiving that colour, fail to do so. Thus as an alternative to supposing that the drug affects A's bodily organs of perception you propose a theory which involves that it affects those of everyone else. To offer such a complicated theory is ridiculous unless one is forced to it. Hence we are left with the usual conclusion that santonin merely affects the organs of perception of the man who takes it; so that the same remote cause which normally makes other people (and the patient when he has not taken the drug) perceive various colours, now makes the patient perceive all things as yellow.

    It only remains now to notice the cases of delirium, dreams, and mystical visions. The case of delirium produced by excess of alcohol or by any cause which makes people have much the same perceptions, is not strictly comparable with that of santonin. For now the patients all perceive the same sort of things, as they did before, but these are no longer anything like what other people perceive. Now under these circumstances we cannot suppose that there is a common remote cause of the perception of the delirious and the normal observer, as we did in the case of the people who have and those who have not taken santonin, and who perceive much the same shapes. Hence this does leave open the possibility that the perceptions of the delirious man have real causes which are remote, but which fail to produce any perceptible effect on the minds of people who have not taken the drug in question. This possibility needs a little further discussion. Of course the mere fact that even a delirious man's perceptions have an adequate cause somewhere is not of any interest in the present question; what we want to know is whether there is any ground for supposing that there exist remote causes for the existence of perceptions of pink rats by people who have drugged themselves with alcohol in the same sense as there exist remote causes for the perceptions of chairs and tables by people in their sober senses. Now I think that in the particular case of a man who sees pink rats with his eyes open there is strong ground for accepting the ordinary view that they are mere appearances in the sense that they have no remote cause which is in any sense a real counterpart of their shape. For pink rats are not things so very different from what ordinary people see every day. There is nothing peculiar about them except the fact that the rats that other people perceive are not of that colour. Moreover, they are localised at places in a room where other people can neither see nor feel anything by a man whose eyes are open. Now it seems to me that it is this close resemblance to the objects of ordinary perception and to the processes of ordinary perception ending in such a surprising discrepancy that is fatal to the belief in real remote causes that only affect the delirious through alcohol. The likeness to what can be perceived by normal people, and the open eyes, suggest that if there were such a remote cause it could not be -- either in itself or in its actions -- unlike the remote causes of our perceptions of chairs and tables and 'real' rats. But then it becomes inexplicable why it should only be able to produce perceptions in people who have habitually drunk to excess, Hence it seems clear that in this case the more normal explanation that these objects are produced entirely centrally, as an effect of the alcohol on the brain, is in all probability the right one.

    When, however, we come to mystical visions in which people agree who have had the same sort of initiation, it seems to me we get further and further away from the case of santonin with which we started and nearer to a position in which the ordinary view of central excitation, though still possible, ceases to be so overwhelmingly the more probable explanation. Mystics often have their experiences when their bodily organs -- at any rate the external ones -- are not in use. Also they frequently say that they cannot describe the experiences that they have had in terms of the objects that they perceive in their normal life. Now it seems to me clear that the less their experiences resemble those of other people, and the less their way of getting them resembles ordinary perception, the less objection there is to the explanation that there is a special real remote cause of them in just the same sense as there is a real remote cause of those perceptions on which ordinary people agree. For it now ceases to be improbable that such real causes should exist and operate without producing perceptions by the usual channels in uninitiated persons.

    I do not wish unduly to labour a point that would be more important for the philosophy of religion or of psychical research than for us, but as I hold that psychical research is a legitimate branch of natural science -- though a difficult and backward one -- I hope that I may be excused for adding a very few reflexions on this matter. There seem to me to be three possible cases to be dealt with if we assume the possibility of genuine veridical mystic vision. It might take the form of perception. In that case the veridical character of the vision would only mean that there really were common causes capable of producing perceptions of certain objects in mystics, but not in other people, and different from the causes of what anybody perceives in the ordinary course of nature. In that case we should be faced by precisely the same sort of problems for mystical vision as we found in ordinary perception, viz. whether anything, and if so what, can be determined about these common real causes from the objects of the perceptions which they cause. Or it might be held that in mystical vision we had true instrumentality, and the objects perceived were the real things. These questions it would be impossible to decide, even if we knew a great deal more about mystic vision than we do. For we have seen that they are far from easy, and can only receive more or less probable answers even for ordinary perception. Finally there is the possibility that what happens in certain mystical states is not a perception, but a feeling that a proposition is self-evident which is not present to other people. I find it difficult to understand what can be meant by, say, perceiving the doctrine of the Trinity. But I can understand that a mn might in a vision become immediately certain of the truth of that doctrine, or that he might have a perception which he held could best be explained by believing that the doctrine was true. But we should have no ground for accepting either his immediate certainty or his explanation of his perception without examination just because he attained them in a vision. He might be, as many of us are in ordinary life, immediately certain of a proposition that is in all probability false; and he might, as we often do, propose as an explanation of his perception which was inadequate, or take as the only possible explanation one to which a more intelligent or experienced person could offer dozens of equally or more probable alternatives.

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Notes ¹ Appearance and Reality, Chap. I, p. 12.

² For any change involves two different states at different moments, and all different moments are all different moments at finite durations apart.

³ Not theoretically, because of radiation pressure.

⁴ Kant's Theory of Knowledge, Chap. IV. passim.

⁵ Op. cit. p. 95.

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Contents -- Chapter 5

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