Professor Marc-Wogau's THEORIE DER SINNESDATA
BY C. D. BROAD
Professor Konrad Marc-Wogau's Die Theorie
der Sinnesdata (Uppsala: A.-B. Lundoquistska Bokhandeln, pp. vi, 449)
is an exceptionally comprehensive book. Four closely connected strands
can be distinguished in it.
In discussing the book I shall ignore Strand 1 almost entirely; for I find very little to criticize in Marc-Wogau's accounts of other men's theories, and there is no point in summarizing
summaries. I shall concentrate my attention mainly on Strands 2 and 3. In connexion with Strand 4 I shall consider only those criticisms of principle which are an important part of Marc-Wogau's defence of his own theory, and some few of the detailed criticisms which happen to have interested me specially.
A very full, fair, and clear synopsis of nearly all the most important
books and papers by writers who have either used, or considered and explicitly
rejected, the 'sense-datum' terminology in discussing the philosophy os
A positive theory on this subject, which differs from that held by any
of these philosophers.
An elaborate discussion of certam general philosophical concepts, such
as the notions of Thing, Existence, Individual, etc. Marc-Wogau
holds that such a discussion is needed, both as the basis for his own theory,
and because the writers with whom he is concerned have used these notions
uncritically and without drawing the necessary distinctions.
Criticisms, both in principle and in detail, on the arguments used and the conclusions reached by the authors whose theories are summarized. These criticisms are based partly on the general results reached in what I have called Strand 3, and are partly independent of these. Their primary object is to show that conclusions at variance with Marc-Wogau's own theory are at any rate unproven. But many of them are of independent interest.
(A) Preliminary Remarks on Terminology.
Before going further I wish to state and exemplify the terminology which I am going to use in discussing the problems raised by Marc-Wogau. It is obviously very important to have a terminology which does not beg any of the numerous questions at issue in his book.
It may be remarked that Marc-Wogau confines himself almost entirely to
cases of visual perception. I shall do this also, though I think that the
tendency among philosophers to make this restriction has had a most unfortunate
effect on their treatment of the problems of sense-perception. In any case
the terminology which I shall use could very easily be adapted to tactual
and to auditory perception.
The most general term which I shall use
is Visual Experience. A feature common and peculiar to all such
experiences is that they are experiences of colour, if we include
under that heading black, white, and grey as well as the various hues.
Now visual experiences may be sub-divided
as follows. There are some which the person who is having them would naturally
describe at the time by saying 'I am seeing so-and-so' or 'I seem to see
so-and-so', or which he would describe in retrospect by saying 'I saw so-and-so'
or 'I seemed to see so-and-so'. We will call these Ostensible Visual
Perceptions. There are others which the experient would naturally describe
by saying 'I had such and such a mental image' or 'I saw so-and-so in my
mind's eye'. We will call these Visual Imagings. We shall be concerned
only with Ostensible Visual Perceptions.
An ostensible visual perception can
be considered from two points of view.
The answer to the second question often has
a very close connexion with the answer to the first. An ostensible visual
perception which is abnormally evoked is generally wholly or largely non-veridical.
An ordinary dream, or the visual experiences of a delirious waking person,
are examples of ostensible visual perceptions which are both abnormally
evoked and non-veridical. But the questions are different, and it is important
to distinguish them for the following reasons. (i) There are plenty of
ostensible visual perceptions which are normally evoked but are non-veridical.
Examples would be the experience called 'seeing a mirage' and in general
any kind of optical illusion. (ii) In the records of psychical research
there is extremely good evidence for the occurrence of ostensible visual
perceptions which are abnormally evoked but are veridical. Examples are
certain dreams and waking hallucinations which agree with certain contemporary
but remote scenes and events to a degree which it would be fantastic to
ascribe to chance-coincidence. Even if all such evidence were rejected,
it would plainly be undesirable to adopt a terminology which ruled out
the possibility of such cases by definition. So I shall sub-divide ostensible
visual perceptions into veridical and non-veridical, and
I shall subdivide each of these classes into normally evoked and
We can ask: 'Is there in fact an object answering to the description
which the experient gives of the object which he claims to be seeing, and
is he in fact perceiving such an object?' This question can be put in the
form: 'Is the ostensible visual perception veridical or non-veridical?'
We can ask: 'Is the ostensible visual perception evoked by light
coming to the percipient's eyes from an external object?' This question
can be put in the form: 'Is the ostensible visual perception normally
evoked or abnormally evoked?'
I think that the word 'see' is commonly
used in such a way that it would be incorrect to say that a person was
'seeing' so-and-so unless one believed that he was having an ostensible
visual perception which was both veridical and normally evoked. Suppose
that one was describing what one knew to be a dream or a waking hallucination.
Then, even if one knew that it corresponded to some distant contemporary
scene to a degree beyond all question of chance-coincidence, one would
say 'He (or I) seemed to see so-and-so', and not 'He (or I) saw
so-and-so'. Suppose that one was describing what one knew to be a misperception.
Then, even if one knew that it was normally evoked, one would use some
such phrase as, e.g., 'I seemed to see a man pointing a gun at me,
but what I really saw was a scarecrow in the twilight'.
Now, whatever may be the case with certain
other kinds of sensible experience, e.g., those of taste or of smell, the
following seems to be true of all or nearly all visual experiences, and
certainly of all those which could be described as ostensible visual perceptions.
It is natural to describe such experiences by using a transitive verb,
viz., 'see' or 'seem to see', followed by a grammatical object which consists
of a general name or an explicit description, e.g., 'a penny', 'a flash
of lightning', 'a brown fiat disk', 'a blue cross on a red field', and
so on. I shall express the fact which I take to lie behind this linguistic
usage by saying that in any ostensible visual perception there can be distinguished
two factors, viz., an act of awareness and an object of awareness.
Now suppose that a person is describing
an ostensible visual perception which he is having. He will very often
use the expression 'I see a so-and-so', where 'so-and-so' is either a general
name for a class of material things, e.g., 'penny', or is an explicit description
of a material thing, e.g., 'flat round disc made of copper and used as
a coin'. If he does this, he is using a description which plainly asserts
or implies a great deal more than is guaranteed by his present visual experience
alone. E.g., to call an object a 'penny' implies that it is something that
could be felt as well as seen, something which other people could see and
touch, something made of copper and issued by the British mint as a coin,
and so on. The expression 'I see a penny' might be used equally by a person
in any of the following situations.
In the second of these examples he says, and says correctly and truly,
that he is seeing a penny, i.e., a round object. But, if he were to confine
himself to describing the object of his awareness as it here and now looks
to him, he would have to say that he is aware of an object that looks elliptical.
In the third of these examples he is altogether mistaken in saying that
he sees a penny, though he may be using the word 'see' correctly relatively
to his beliefs at the time; for his ostensible perception is neither veridical
nor normally evoked. He would admit this when he recovered his normal state
and it was explained to him that he had been hypnotized. But, if he had
confined himself to saying: 'I have a visual awareness of an object that
looks brown, and flat and round and, in short, penny-like', there is no
reason to suppose that he would have been mistaken.
A person who was looking straight down on a penny lying on his table
A person who was looking so obliquely at a penny lying on his table
that it looked elliptical and not round.
A person under hypnotic suggestion who had a visual hallucination of
seeing a penny on his table, though there was in fact no such object there
at the time.
For these reasons it is essential to distinguish
conceptually the following two notions, viz.,
The distinction may be drawn as follows.
Suppose that the experient, in describing such an experience, were to confinee
himself to describing how its object here and now looks to him. Then I
should call the object thus described a visual prehensum; and I
should say that it is visually prehended as having those characteristics
and only those which the experient would ascribe to it if he confined himself
entirely to describing how it here and now looks to him. Suppose, on the
other hand, that the experient, in describing his ostensible visual perception,
does not thus limit himself. He describes it by reference to an object
which he asserts or implies to have characteristics other than those which
are here and now visually presented to him. He does this, no doubt, on
the basis of his present visual prehension, but he goes beyond (and
perhaps even against) what he here and now visually prehends. Then I should
call the actual or possible object thus described an ostensible visum.
- thc object which is visually prehended, and
- the object which is ostensibly seen, in any ostensible visual perception.
The examples given above illustrate the
- There may be nothing at all corresponding to the ostensible
visum of an ostensible visual perception, i.e., nothing actual which remoteiy
answers to the description of that possible object. In that case the visual
experience may be described as wholly delusive. But there will still
be a certain visual prehensum, and there may be no reason whatever to doubt
that it has the properties which the experient would ascribe to it.
- The description of the ostensible visum will always include
or imply properties which are not visually prehended in the prehensum.
Some of these may be properties which could not be visually prehended,
e.g., coldness and smoothness. Some of them may be properties which could
not be sensibly presented at all, because they involve what I call
'categorial characteristics' such as cause and substance. Examples would
be causal and dispositional properties, such as impenetrability, mass,
- The description of the ostensible visum may include or imply
a certain determinate characteristic which could be visually prehended
but which differs specifically from one which the prehensum is prehended
as having. E.g., when the penny is viewed very obliquely the prehensum
is prehended as elliptical, but the description of the ostensible visum
as a "penny" implies that the latter is round. But in this case
there is something answering to the description of the ostensible visum.
The ostensible visual perception here may be said to be wholly veridical.
For the ellipticity which the prehensum is prehended as having does not
lead the percipient to ascribe ellipticity to the visum; on the contrary,
in conjunction with certain other features in the total prehensum, it leads
him to ascribe roundness to the visum.
- There are plenty of intermediate cases where there is good
reason to believe that an ostensible visual perception is neither wholly
delusive nor wholly veridical. There is something actual which answers
in the main to the description of the ostensible visum, and which the percipient
is perceiving; but it differs in certain details from the latter. In such
cases we may say that the visual experience is veridical in principle
but delusive in certain details.
When an ostensible visual perception is
not wholly delusive we can talk of its actual visum, and we can
compare this with the description of that possible object which is its
I can hardly hope that this terminology
is impeccable, but I hope that it may serve. It is intended to leave open
for discussion the following questions.
- Suppose that there is an actual visum, answering completely
or in principle to the description of the ostensible visum of a certain
visual experience. What is the relation of the visual prehensum to the
actual visum? Are they necessarily different entities, inter-related
in some specially intimate way? Or is it possible that the visual prehensum
and the actual visum may be one and the same entity under different
descriptions, as, e.g., the Prime Minister of England and the Leader of
the House of Commons might be?
- If this is possible, is there any good reason for or against
holding that it is true?
- Is it possible for a visual prehensum to have characteristics
besides those which it is visually prehended as having, e.g., to
be in fact cold and smooth as well as brown and elliptical?
- Is it possible for a visual prehensum to have characteristics
incompatible with some of those which it is visually prehended as
having, e.g., to be in fact round though it is visually prehended as elliptical?
It is plain that the answers to Questions 3 and 4 may have an important
bearing on the answers to Questions 1 and 2. These are the kind of questions
which Marc-Wogau is mainly concerned to discuss, and I am naturally anxious
to use a terminology which shall not beg any of them.
(B) Preliminary Sketch of Marc-Wogau's Theory.
We can now give a very rough preliminary
sketch of Marc-Wogau's main contentions in Strands 2 and 3. I think that
the following are the most important points.
(1) He thinks that most writers who
would commonly be described as supporters of some form of the Sense-datum
Theory have held that the visual prehensum and the actual visum are different
entities even when the visual perception is wholly veridical. They have
held various views about the nature of the actual visum, and correspondingly
various views about the nature of the relation between the visual prehensum
and the actual visum. But they have never admitted that the visual prehension
and the actual visum could be one and the same entity under different descriptions;
and they have produced many arguments to show either that this is impossible
or that it is never in fact true.
(2) Most of them have either explicitly
asserted or tacitly assumed that a visual prehensum can have no characteristics
besides those which it is visually prehended as having, and a
fortiori that it can have no determinate characteristic incompatible
with any which it is prehended as having. If either of these contentions
is admitted, Question 1 above must be answered in the following way. A
penny, e.g., is certainly a round hard thing made of copper; and what I
visuallv prehend when I look at a penny is never prehended as hard or made
of copper, whilst it is prehended as elliptical and not as round
if I am looking very obliquely at the penny. Therefore, unless what I visually
prehend can have certain characteristics besides those which I prehend
it as having, and certain determinate characteristics incompatible with
some of those which I prehend it as having, it cannot be identical with
the penny which is the actual visum.
(3) Marc-Wogau holds that in certain
cases, e.g., when a penny is looked at directly and not very obliquely
from about arm's length in normal light by a person in the mental attitude
of ordinary practical life, there is no reason to doubt that what is visually
prehended is in a certain sense identical with the actual visum,
i.e., with the penny itself. In other cases, e.g., when the penny is looked
at in a very oblique direction or from a very great distance or when the
observer is in certain other mental attitudes, the visual prehension is
certainly not identical in that sense with the actual visum. It
is then an entity which stands in a certain peculiar relation to a certain
other qualitatively different entity, viz., the penny itself. In such cases,
and a fortiori in wilder cases, such as vision in a mirror, waking
hallucination, dreaming, etc., it is proper to speak of the visual prehensum
as a 'sense-datum'.
It will now be clear why Marc-Wogau discusses
certain very general problems which are not usually treated explicitly
by writers on the philosophy of sense-perception. The fundamental question
at issue is whether the prehensum and the actual visum of a visual perception
are ever identical or must always be different. Therefore
the various meanings of 'identity' anti 'difference' need to be discussed.
Again, the actual visum is in general a material thing, e.g., a
penny. Therefore it is necessary to discuss the notion of 'material thing'.
Therefore it is desirable to consider the following two notions, viz.,
- the identity of a thing through time and change, and
- the relations between one thing and its many appearances at
a given moment.
Now among the reasons which have been given
for holding that the visual prehensum and the actual visum are always different
the following have been prominent.
It is therefore desirable to clear up the notions of 'existence'
and of 'particular individual' and to point out any ambiguities which may
lurk in them.
- It has been alleged that the prehensum of any visual experience
certainly exists, whilst it is always possible to doubt whether
anything exists answering to the description of the ostensible visum.
- It has been alleged that the visual prehensum is always a particular
individual, whilst a material thing is of a different logical type,
e.g., a class.
Marc-Wogau's discussions of these several
very general problems occur at various parts of his book, interspersed
between the treatments of much more detailed problems specially concerned
with sense-perception. It seems to me to be convenient, now that I have
explained why Marc-Wogau thinks it necessary to deal with these general
problems, to take them all together and to clear them out of the way at
the beginning. For Marc-Wogau's arguments and conclusions about specific
problems in the philosophy of sense-perception depend in part on his answers
to these general questions.