|C. D. Broad, Scientific Thought , 1923|
THE SENSATIONAL AND PERCEPTUAL BASIS OF OUR SCIENTIFIC CONCEPTS
"Fallunt nos oculi, vagique sensus
Oppressa ratione mentiuntur.
Nam turris, prope quae quadrata surgit,
Detritis procul angulis rotatur."
Matter and its Appearances; Preliminary Definitions
In the First Part we have been dealing with the gradual development and modification of the traditional scientific concepts of Space, Time, and Motion, within the region of Physics. These concepts were taken over by science from educated common-sense, and we have been tracing the process of clarification and definition which they have undergone at the hands of scientists in pursuit of their own business. At two places only have we deliberately gone outside the range of ordinary scientific reflection. The first was where we explained the Principle of Extensive Abstraction, and tried to justify by its means what mathematical physicists take for granted, viz., the application of geometry and mechanics, stated in terms of points, instants, and particles, to a world of extended objects and non-instantaneous events. The second was where we dealt with the general problem of Time and Change, and tried to defend their reality against the very plausible objections which have been made to them by certain philosophers.
Now the careful reader will have been struck by two points in Part 1. (1) He will have noticed that the "raw material," which science took over from common-sense and elaborated, was really anything but "raw." It was already highly complex and sophisticated. The common-sense notions of a single Space, a single Time, and persistent bits of Matter which exist, move, and change within them, are by no means primitive. They must be the results of a long and complex process of reflection and synthesis, carried out by countless generations of men on the crude deliveries of their senses, embodied in everyday speech, and thus handed down from father to son for further elaboration. The main outlines of this conceptual scheme have been accepted without question by scientists, and we have so far merely been tracing those modifications of detail within the scheme, which a more accurate knowledge of the facts of nature has shown to be necessary. In Part II, I want to dig below the foundations of Part I, and to try to connect the concepts of science and common-sense with their roots in crude sensation and perception. If we should find, as I think we shall, that recent modifications in the traditional concepts, which have been made on purely scientific grounds bring the general scheme into closer connexion with its sensible and perceptual basis, this will be an additional argument in favour of such modifications, and should tend to neutralise the impression of paradox which these later developments produce on men who have been brought up on the traditional scheme.
(2) The second point which will have struck the reader is that practically nothing has been said so far about the concept of Matter. This is true. There is a much wider divergence between the common-sense and the scientific concepts of Matter than between the two concepts of Space or of Time. The scientific concepts of Space and Time are fairly straightforward developments and clarifications of the concepts of common-sense. But common-sense thinks of Matter as having many intrinsic qualities, such as colour, temperature, etc., besides its merely spatio-temporal characteristics. Science, on the other hand, tends to think of Matter as being simply "the movable in space," and to ascribe to it no intrinsic non-spatio-temporal qualities except mass. Now the treatment of Matter and our knowledge of it will bring us in the most direct way to the heart of the problem of Part II. Matter is admitted to be, or to be specially closely connected with, what we perceive with our senses. And again, it would be admitted by most people that we should never have known of spatial attributes like shape, size, and position, if we had not perceived bits of matter of various shapes and sizes in various places. Lastly, we learn about Motion by watching bits of Matter moving about, and by moving about ourselves. Thus, in trying to clear up the relations between Matter, as conceived by science, and what we perceive with our senses, we shall at the same time be dealing with thee sensible and perceptual bases of the concepts of Space, Time, and Motion. So, in one sense, this Part will be wholly about the concept of Matter. But this will involve a reconsideration of the concepts of Space, Time, and Motion. I shall begin by stating the problem in its most general form, and shall gradually go into greater detail.
The Traditional Notion of a bit of Matter. -- When we ask what is meant by a bit of Matter the question is itself ambiguous. In one sense a complete answer to it would be a complete theory of Matter, and this could only be made, if at all, at the very end of our discussion. This, however, is not the sense in which I am asking the question here. All that I am asking is: "What is the irreducible minimum of properties which practically everybody would agree that an object must possess if it is to be called a bit of Matter?" I think that science and common-sense would agree that at least the following conditions must be fulfilled: (i) Its existence and properties must be independent of the minds that happen to observe it, and it must be capable of being observed by many minds. This characteristic may be summed up by saying that Matter is neutral as between various observers, or is "public" -- to use a convenient word of Mr Russell's. This distinguishes Matter sharply from any ordinary conscious state of mind. The latter is in a unique way private to the person whose state it is. My belief that 2 + 2 = 4 is different from yours, though the two beliefs refer to the same fact. My belief cannot literally wander out of my mind and turn up in yours. It is true that I may convert you from your erroneous belief that 2 + 2 = 5, and replace it by my true belief that 2 + 2 = 4. This does not, however, mean that my belief has become yours, in the sense that it has left my mind and taken up its abode in yours. Were this so, I could never persuade you of anything without losing my own belief in it, and schoolmasters would presumably be distinguished from other men by an ultra-Humian scepticism as to all the subjects that they teach. This is not, in fact, found to be the case. All that really happens when A converts B to his own belief is that A's arguments, or the amount of A's bank balance, produce in B's mind a state of belief which refers to the same fact as B's belief, and has the same relation of concordance or discordance to this fact. My belief and yours are only called the same belief in the derivative sense that they are two different acts of believe which are related in the same way : to the same fact.
Exactly the same is true of desires. We do sometimes say that you and I have the same desire; but what we mean is that your desire and mine, though two states of mind, have a single object. Now, if there be such things as bits of Matter at all, they are not private in this way to each mind, but are common to all the minds that observe them. We talk of my beliefs and your wishes; we do not talk of my hydrogen atom or of your electron. We just speak of the or this atom or electron. It is, of course, true that a hat or an umbrella is regarded as a bit of Matter, and that we do talk of my hat and of your umbrella. But this, which at first sight seems an objection, is seen on further reflection to support what we have been saying. The sense in which my umbrella is mine is different from that in which my beliefs are mine. My umbrella is mine only in the sense that it is legally my property; my beliefs are mine in the sense that they could not exist out of my mind or pass into yours. You cannot take my beliefs; it is only too fatally easy for you to take my umbrella. So that even those bits of Matter to which we apply possessive adjetives are public in a way in which no state of mind is public.
(ii) A bit of Matter is supposed to be neutral, not only between different observers, but also to be in a certain way neutral as between several senses of the same observer. We are said to see, hear, and feel a bell. This sort of neutrality is not supposed to be complete. The shape and size of the bell are indeed supposed to be in some way common to sight and touch. As regards its sensible qualities the view of common-sense is that any bit of Matter combines a number of these, and that different senses are needed to reveal different sensible qualities. Thus sight, and it alone, makes us aware of the colours of bodies; touch, and it alone, makes us aware of their temperatures; and so on. But it is part of the ordinary view of a piece of Matter that all these various sensible qualities co-exist in it, whether the requisite senses be in action to reveal them all or not. If we first only look at a body, and then shut our eyes and go up to it and feel it, it is not supposed that it had no temperature on the first occasion and no colour on the second.
(iii) These two properties of publicity, as between different observers, and neutrality, as between the various senses of a single observer, are closely connected with a third feature which is held to be characteristic of Matter. Bits of Matter are supposed to persist with very little change, whether anyone happens to observe them or not, and to pursue their own affairs and interact with each other, regardless of our presence and absence.
(iv) This brings us to the fourth characteristic of Matter. It is commonly held to be part of what we mean by a bit of Matter that it shall have a more or less permanent shape and size, and that it shall have a position in Space, and be capable of moving from one position to another. It is admitted that bits of Matter are constantly changing their shapes, sizes, and positions; but it is held that they do this through their interactions with each other and not through any change in our acts of observation, and that in all their changes they continue to have some shape, size and position. If it could be shown that nothing in the world actually has such properties as these, it would commonly be held that the existence of Matter had been disproved, even though there were public, independent, and persistent objects.
Berkeley, e.g., is commonly held to have denied the existence of Matter, and he certainly thought himself that he had done so. Yet Berkeley's theory undoubtedly involves the existence of certain entities, viz., the volitions (and perhaps the sensations) of God, which are independent of the mind of any finite observer and are neutral as between my mind and yours. The reason why we say that, if Berkeley be right, there is no Matter, is because the volitions of God, though neutral and independent of us observers, have nothing corresponding to shape, size, and position; whilst the only entities which Berkeley allows to have these attributes, viz., our sensations, are private to each of us, and exist only so long as we have them. Very few philosophers have denied that there are entities answering to the first three conditions, but a great many have denied that there are any answering both to these and to the fourth condition. Such philosophers are held by themselves and by common-sense to have denied the existence of Matter. Now we shall have plenty of opportunity for seeing that there is a real difficulty in holding that the entities which have shapes, sizes, and positions are neutral and independent, and that those which are neutral and independent have shapes, sizes, and positions.
Before we consider these points in detail at all we must mention an additional complication which, though partly verbal, is sure to puzzle us if we do not resolutely drag it into the light. No doubt it is part of what we mean by a bit of Matter that it shall, in some sense, have shape, size, and position. But in how literal a sense must this be true? We have already seen that, in some sense, an extension or a duration is composed of points or of instants respectively. But this sense is highly complicated and sophisticated, or, to use a happy phrase of Dr G. E. Moore's, "Pickwickian." Now we shall doubtless be able to find Pickwickian senses in which there are entities that are at once public and extended. The question is: How Pickwickian may the terms in our statement become before it ceases to be useful, and becomes merely misleading, to say that we accept the existence of matter? Our theological friends have much the same difficulties in their interpretations of the terms that are used in the Creeds. It could obviously only be true in a highly Pickwickian sense that the Second Person of the Trinity is the son of the First. No one supposes it to be true in the literal sense in which George V is the son of Edward VII; and the only substantial point at issue is whether the sense in which it might he true (assuming, for the sake of argument, that the Persons exist) is not so extremely Pickwickian that the statement is more likely to mislead than to enlighten. Fortunately for us the terminology of our problem is not surrounded with the same emotional fringe as surrounds the terms used in Theology. It is no part of our duty to pay compliments to Matter, and so long as we state clearly what we do mean, it is of little importance whether our terms be used in a literal or in a highly Pickwickian sense. It will be a question of taste whether it shall be said that the theory that we finally adopt amounts to the acceptance or the denial of Matter. If we should be accused of saying that "Matter is not Matter," we shall at least be better off than *Dr F. R. Tennant, who labours under the dreadful imputation of teaching that "Sin is not sin."
The Notion of Sensible Appearance. -- I have now tried to point out what is the irreducible minimum of properties which ordinary people consider must be possessed by anything if it is to count as a piece of Matter. I have also pointed out, by anticipation, that the history of philosophy shows there to be a great difficulty in holding that there are any entities which fulfil all these conditions in a literal sense. Lastly, we have noticed that the question of the reality or unreality of Matter, thus defined, is not perfectly clear-cut, because of the practical certainty that many of our terms will have to be interpreted in a more or less Pickwickian manner, and the doubt whether it is worth while to go on using familiar phrases after their literal meaning has been departed from beyond a certain point. We must now consider what facts make it hard to believe that anything obeys all four conditions in at all a literal sense.
The difficulty arises because of the group of facts which we sum up by saying that it is necessary to distinguish between things as they are and things as they seem to us, or between physical reality and sensible appearance. Difficulties always arise when two sets of properties apparently belong to the same objects and yet are apparently incompatible with each other. Now the difficulty here is to reconcile the supposed neutrality, persistence, and independence of a physical object with the obvious differences between its various sensible appearances to different observers at the same moment, and to the same observer at different moments between which it is held not to have undergone any physical change. We know, e.g., that when we lay a penny down on a table and view it from different positions it generally looks more or less elliptical in shape. The eccentricity of these various appearances varies as we move about, and so does the direction of their major axes. Now we hold that the penny, at which we say that we were looking all the time, has not changed; and that it is round, and not elliptical, in shape. This is, of course, only one example out of millions. It would be easy to offer much wilder ones; but it is simple and obvious, and involves no complications about a transmitting medium; so we will start with it as a typical case to discuss.
Now there is nothing in the mere ellipticity or the mere variation, taken by itself, to worry us. The difficulty arises because of the incompatibility between the apparent shapes and the supposed real shape, and between the change in the appearances and the supposed constancy of the physical object. We need not at present ask we why we believe that there is a single physical object with these characteristics, which appears to us in all these different ways. It is a fact that we do believe it. It is an equally certain fact that the penny does look different as we move about. The difficulty is to reconcile the different appearances with the supposed constancy of the penny, and the ellipticity of most of the appearances with the supposed roundness of the penny. It is probable that at first sight the reader will not see much difficulty in this. He will be inclined to say that we can explain these various visual appearances by the laws of perspectives and so on. This is not a relevant answer. It is quite true that we can predict what particular appearance an object will present to an observer, when we know the shape of the object and its position with respect to the observer. But this is not the question that is troubling us at present Our question is as to the compatibility of these changing elliptical appearances, however they may be correlated with other facts in the world, with the supposed constancy and roundness of the physical object.
Now what I call Sensible Appearance is just a general name for such facts as I have been describing. It is important here as always to state the facts in a form to which everyone will agree, before attempting any particular analysis of them, with which it is certain that many people will violently disagree. The fundamental fact is that we constantly make such judgments as: "This seems to me elliptical or red, or hot," as the case may be and that about the truth of these judgments we do not feel the least doubt. We may, however, at the same time doubt or positively disbelieve that this is elliptical, or red, or hot. I may be perfectly certain at one and the same time that I have the peculiar experience expressed by the judgment: "This looks elliptical to me," and that in fact the object is not elliptical but is round.
I do not suppose that anyone, on reflection, will quarrel with this statement of fact. The next question is as to the right way to analyse such facts; and it is most important not to confuse the facts themselves with any particular theory as to how they ought to be analysed. We may start with a negative remark, which seems to me to be true, and is certainly of the utmost importance if it be true. Appearance is not merely mistaken judgment about physical objects. When I judge that a penny looks elliptical I am not mistakenly ascribing elliptical shape to what is in fact round. Sensible appearances may lead me to make a mistaken judgment about physical objects, but they need not, and, so far as we know, commonly do not. My certainty that the penny looks elliptical exists comfortably alongside of my conviction that it is round. But a mistaken judgment that the penny is elliptical would not continue to exist after I knew that the penny was really round. The plain fact is then that "looking elliptical to me" stands for a peculiar experience, which, whatever the right analysis of it may be, is not just a mistaken judgment about the shape of the penny.
Appearance then cannot be described as mistaken judgment about the properties of some physical object. How are we to describe it, and can we analyse it? Two different types of theory seem to be possible, which I will call respectively the Multiple Relation Theory, and the 0bject Theory of sensible appearance. The Multiple Relation Theory takes the view that "appearing to be so and so" is a unique kind of relation between an object, a mind, and a characteristic. (This is a rough statement, but it will suffice for the present.) On this type of theory to say that the penny looks elliptical to me is to say that a unique and not further analysable relation of "appearing" holds between the penny, my mind, and the general characteristic of ellipticity. The essential point for us to notice at present about theories of this kind is that they do not imply that we are aware of anything that really is elliptical when we have the experience which we express by saying that the penny looks elliptical to us. Theories of this type have been suggested lately by Professor Dawes Hicks and by Dr G. E. Moore. So far, they have not been worked out in any great detail, but they undoubtedly deserve careful attention. Theories of the Object type are quite different. They do not involve a unique and unanalysable multiple relation of "appearing" but a peculiar kind of obiect -- an "appearance." Such objects, it is held, actually do have the characteristics which the physical object seems to have. Thus the Object Theory analyses the statement that the penny looks to me elliptical into a statement which involves the actual existence of an elliptical object, which stands in a certain cognitive relation to me on the one hand, and in another relation, yet to be determined, to the round penny. This type of theory, though it has been much mixed up with irrelevant matter, and has never been clearly stated and worked out till our own day, is of respectable antiquity. The doctrine of "representative ideas" is the traditional and highly muddled form of it. It lies at the basis of such works as Russell's Lowell Lectures on the External World. In this book I shall deliberately confine myself to this type of theory, and shall try to state it clearly, and work it out in detail. The following additional works may be consulted with advantage:
- G. E. Moore,
- Philosophical Studies, V. and VII.
- G. D. Hicks
- Proceedings of the Aristotelian Society, 1913, 1916.
- G. F. Stout
- Manual of Psychology, Bk. III., Part II. Cap. I.
- Proceedings of the Aristotelian Society, 1913.
Notes * See his Origin of Sin.
Contents -- Go to Chapter VIII