The term "sense-data" is ambiguous; and therefore I think I had better
begin by trying to explain what the class of entities is whose status I
propose to discuss.
There are several different classes of mental events, all of which,
owing to their intrinsic resemblance to one another in certain
respects, may, in a wide sense, be called "sensory experiences,"
although only some among them would usually be called "sensations."
There are (1) those events, happening in our minds while we are
awake, which consist in the experiencing of one of those entities,
which are usually called "images," in the narrowest sense of the
term. Everybody distinguishes these events from sensations proper;
and yet everybody admits that "images" intrinsically resemble the
entities which are experienced in sensations proper in some very
important respect. There are (2) the sensory experiences we have in
dreams, some of which would certainly be said to be experiences of
images, while others might be said to be sensations. There are (3)
hallucinations, and certain classes of illusory sensory experiences.
There are (4) those experiences, which used to be called the having
of "after-images," but which psychologists now say ought rather to
be called "after-sensations." And there are, finally, (5) that class
of sensory experiences, which are immensely commoner than any of the
above, and which may be called _sensations proper_, if we agree to use
this term in such a way as to exclude experiences of my first four
sorts.
Every event, of any one of these five classes, consists in the fact
that an entity, of some kind or other, _is experienced._ The entity
which is experienced may be of many different kinds; it may, for
instance, be a patch of colour, or a sound, or a smell, or a taste,
etc; or it may be an image of a patch of colour, an image of a
sound, an image of a smell, an image of a taste, etc. But, whatever
be its nature, the entity which _is_ experienced must in all cases
be distinguished from the fact or event which consists in its being
experienced; since by saying that it is experienced we mean that it
has a relation of a certain kind to something else. We can, therefore,
speak not only of _experiences_ of these five kinds, but also of the
entities which _are experienced in_ experiences of these kinds; and
the entity which is experienced _in_ such an experience is never
identical with the experience which consists in its being experienced.
But we can speak not only of the entities which _are_ experienced in
experiences of this kind, but also of _the sort_ of entities which are
experienced in experiences of this kind; and these two classes may
again be different. For a patch of colour, even if it were not actually
experienced, would be an entity _of the same sort_ as some which are
experienced in experiences of this kind: and there is no contradiction
in supposing that there are patches of colour, which yet are not
experienced; since by calling a thing a patch of colour we merely make
a statement about its intrinsic quality, and in no way assert that
it has to anything else any of the relations which may be meant by
saying that it is experienced. In speaking, therefore, of _the sort
of_ entities which are experienced in experiences of the five kinds I
have mentioned, we do not necessarily confine ourselves to those which
actually _are_ experienced in some such experience: we leave it an open
question whether the two classes are identical or not. And the class
of entities, whose status I wish to discuss, consists precisely of all
those, whether experienced or not, which are _of the same sort_ as
those which are experienced in experiences of these five kinds.
I intend to call this class of entities the class of _sensibles_; so
that the question I am to discuss can be expressed in the form: What
is the status of sensibles? And it must be remembered that images and
after-images are just as much "sensibles," in my sense of the term, as
the entities which are experienced in sensations proper; and so, too,
are any patches of colour, or sounds, or smells, etc, (if such there
be), which are not experienced at all.
In speaking of sensibles as _the sort of_ entities which are
experienced in sensory experiences I seem to imply that all the
entities which are experienced in sensory experiences have some
common characteristic other than that which consists in their being
so experienced. And I cannot help thinking that this is the case,
in spite of the fact that it is difficult to see what intrinsic
character can be shared in common by entities so different from one
another as are patches of colour, sounds, smells, tastes, etc. For,
so far as I can see, some non-sensory experiences may be exactly
similar to sensory ones in all intrinsic respects, except that what
is experienced in them is different in kind from what is experienced
in any sensory experience: the relation meant by saying that in them
something _is experienced_ may be exactly the same in kind, and so may
the experient. And, if this be so, it seems to compel us to admit that
the distinction between sensory and non-sensory experiences is derived
from that between sensibles, and non-sensibles and not _vice versâ._ I
am inclined, therefore, to think that all sensibles, in spite of the
great differences between them, have some common intrinsic property,
which we recognise, but which is unanalysable; and that, when we call
an experience sensory, what we mean is not only that in it something
is experienced in a particular way, but also that this something has
this unanalysable property. If this be so, the ultimate definition of
"sensibles" would be merely all entities which have this unanalysable
property.
It seems to me that the term "sense-data" is often used, and may be
correctly used, simply as a synonym for "sensibles"; and everybody,
I think, would expect me, in discussing the status of sense-data,
to discuss, among other things, the question whether there are any
sensibles which are not "given." It is true that the etymology of the
term "sense-data" suggests that nothing should be called a sense-datum,
but what _is_ given; so that to talk of a non-given sense-datum would
be a contradiction in terms. But, of course, etymology is no safe guide
either as to the actual or the correct use of terms; and it seems to me
that the term "sense-data" is often, and quite properly, used merely
for _the sort of_ entities that are given in sense, and not in any way
limited to those which are actually given. But though I think I might
thus have used "sense-data" quite correctly instead of "sensibles,"
I think the latter term is perhaps more convenient; because though
nobody ought to be misled by etymologies, so many people in fact are
so. Moreover the term "sense-data" is sometimes limited in yet another
way, viz, to the sort of sensibles which are experienced in _sensations
proper_; so that in this sense "images" would not be "sense-data."
For both these reasons, I think it is perhaps better to drop the term
"sense-data" altogether, and to speak only of "sensibles."
My discussion of the status of sensibles will be divided into two
parts. I shall first consider how, in certain respects, they are
related to our minds; and then I shall consider how, in certain
respects, they are related to physical objects.
(I)
(1) We can, I think, distinguish pretty clearly at least one kind
of relation which sensibles, of all the kinds I have mentioned, do
undoubtedly sometimes have to our minds.
I do now see certain blackish marks on a whitish ground, and I hear
certain sounds which I attribute to the ticking of my clock. In both
cases I have to certain sensibles--certain blackish marks, in the one
case, and certain sounds, in the other--a kind of relation with which
we are all perfectly familiar, and which may be expressed, in the one
case, by saying that I actually _see_ the marks, and in the other, by
saying that I actually _hear_ the sounds. It seems to me quite evident
that the relation to the marks which I express by saying that I _see_
them, is not different in kind from the relation to the sounds which
I express by saying that I _hear_ them. "Seeing" and "hearing," when
thus used as names for a relation which we may have to sensibles, are
not names for different relations, but merely express the fact that,
in the one case, the kind of sensible to which I have a certain kind
of relation is a patch of colour, while, in the other case, the kind
of sensible to which I have the same kind of relation is a sound. And
similarly when I say that I feel warm or smell a smell these different
verbs do not express the fact that I have a different kind of relation
to the sensibles concerned, but only that I have the _same_ kind of
relation to a different kind of sensible. Even when I call up a visual
image of a sensible I saw yesterday, or an auditory image of a sound
I heard yesterday, I have to those images exactly the same kind of
relation which I have to the patches of colour I now see and which I
had yesterday to those I saw then.
But this kind of relation, which I sometimes have to sensibles of
all sorts of different kinds, images as well as others, is evidently
quite different in kind from another relation which I may also have
to sensibles. After looking at this black mark, I may turn away my
head or close my eyes, and then I no longer _actually see_ the mark I
saw just now. I may, indeed, have (I myself actually do have at this
moment) a visual _image_ of the mark before my mind; and to this image
I do now have exactly the same kind of relation which I had just now
to the mark itself. But the image is not identical with the mark of
which it is an image; and to the mark itself it is quite certain that
I have _not_ now got the same kind of relation as I had just now, when
I was actually seeing it. And yet I certainly may _now_ have to that
mark itself a kind of relation, which may be expressed by saying that
I am _thinking of_ it or remembering it. I can _now_ make judgments
about _it itself_--the very sensible which I did see just now and am no
longer seeing: as, for instance, that I did then see it and that it was
different from the image of it which I am now seeing. It is, therefore,
quite certain that there is a most important difference between the
relation I have to a sensible when I am actually seeing or hearing it,
and any relation (for there may be several) which I may have to the
same sensible when I am only thinking or or remembering it. And I want
to express this difference by using a particular term for the former
relation. I shall express this relation, which I certainly do have to
a sensible when I actually see or hear it, and most certainly do not
have to it, when I only think of or remember it, by saying that there
is in my mind a _direct apprehension_ of it. I have expressly chosen
this term because, so far as I know, it has not been used hitherto as
a technical term; whereas all the terms which have been so used, such
as "presented," "given," "perceived," seem to me to have been spoilt
by ambiguity. People sometimes, no doubt, use these terms as names for
the kind of relation I am concerned with. But you can never be sure,
when an entity is said to be "given" or "presented" or "perceived,"
that what is meant is simply and solely that it has to someone that
relation which sensibles do undoubtedly have to me when I actually see
or hear them, and which they do _not_ have to me when I only think of
or remember them.
I have used the rather awkward expression "There is in my mind a
direct apprehension of this black mark," because I want to insist that
though, when I see the mark, the mark certainly has to _something_
the fundamental relation which I wish to express by saying that it is
directly apprehended, and though the event which consists in its being
directly apprehended by that something is certainly a mental act of
_mine_ or which occurs in my mind, yet the something which directly
apprehends it may quite possibly not be anything which deserves to be
called "I" or "me." It is quite possible, I think, that there is _no_
entity whatever which deserves to be called "I" or "me" or "my mind";
and hence that nothing whatever is ever directly apprehended by _me._
Whether this is so or not, depends on the nature of that relation which
certainly does hold between all those mental acts which are _mine_, and
does not hold between any of mine and any of yours; and which holds
again between all those mental acts which are yours, but does not hold
between any of yours and any of mine. And I do not feel at all sure
what the correct analysis of this relation is. It may be the case
that the relation which unites all those acts of direct apprehension
which are mine, and which is what we mean to say that they have to one
another when we say they are all mine, really does consist in the fact
that one and the same entity is _what_ directly apprehends in each of
them: in which case this entity could properly be called "me," and it
_would_ be true to say that, when I see this black mark, _I_ directly
apprehend it. But it is also quite possible (and this seems to me to
be the view which is commonest amongst psychologists) that the entity
which directly apprehends, in those acts of direct apprehension which
are mine, is numerically different in every different act; and that
what I mean by calling all these different acts _mine_ is either merely
that they have some kind of relation to _one another_ or that they
all have a common relation to some other entity, external to them,
which may or may not be something which deserves to be called "me."
On any such view, what I assert to be true of this black mark, when
I say that it is seen by me, would not be simply that it is directly
apprehended by me, but something more complex in which, besides
direct apprehension, some other quite different relation was also
involved. I should be asserting _both_ (1) that the black mark is being
directly apprehended by _something_, _and_ (2) that this act of direct
apprehension has to something else, external to it, a quite different
relation, which is what makes it an act of _mine._ I do not know how to
decide between these views, and that is why I wished to explain that
the fundamental relation which I wish to call direct apprehension, is
one which quite possibly never holds between _me_ and any sensible.
But, once this has been explained, I think no harm can result from
using the expression "I directly apprehend A" as a synonym for "A
direct apprehension of A occurs in my mind." And in future I shall so
speak, because it is much more convenient.
The only other point, which seems to me to need explanation, in order
to make it quite clear what the relation I call "direct apprehension"
is, concerns its relation to _attention_; and as to this I must confess
I don't feel clear. In every case where it is quite clear to me that
I am directly apprehending a given entity, it seems also clear to me
that I am, more or less, attending to it; and it seems to me possible
that what I mean by "direct apprehension" may be simply identical with
what is meant by "attention," in _one_ of the senses in which that word
can be used. That it can, at most, only be identical with _one_ of the
relations meant by attention seems to me clear, because I certainly
can be said to attend, in some sense or other, to entities, which I am
not directly apprehending: I may, for instance, think, with attention,
of a sensible, which I saw yesterday, and am certainly not seeing now.
It is, therefore, clear that to say I am attending to a thing and yet
am _not_ directly apprehending it, is not a contradiction in terms:
and this fact alone is sufficient to justify the use of the special
term "direct apprehension." But whether to say that I am directly
apprehending a given thing and yet am _not_ attending to it, in any
degree at all, is or is not a contradiction in terms, I admit I don't
feel clear.
However that may be, one relation, in which sensibles of all sorts do
sometimes stand to our minds, is the relation constituted by the fact
that we directly apprehend them: or, to speak more accurately, by the
fact that events which consist in their being directly apprehended are
_in_ our minds, in the sense in which to say that an event is _in_ our
minds means merely that it is a mental act of _ours_--that it has to
our other mental acts that relation (whatever it may be) which we mean
by saying that they are all mental acts _of the same individual._ And
it is clear that to say of a sensible that it is directly apprehended
by me, is to say of it something quite different from what I say of a
mental act of mine, when I say that this _mental act is in my mind_:
for nothing is more certain than that an act of direct apprehension or
belief may be in my mind, without being itself directly apprehended
by me. If, therefore, by saying that a sensible is _in our minds_
or is _ours,_ we mean merely that it is directly apprehended by us,
we must recognise that we are here using the phrases "in our minds"
or "ours" in quite a different sense from that in which we use them
when we talk of our mental acts being "in our minds" or "ours." And
why I say this is because I think that these two relations are very
apt to be confused. When, for instance, we say of a given entity that
it is "experienced," or when the Germans say that it is "erlebt," it
is sometimes meant, I think, merely that it is directly apprehended,
but sometimes that it is in my mind, in the sense in which, when I
entertain a belief, this act of belief is in my mind.
But (2) it seems to me to be commonly held that sensibles are often
in our minds in some sense quite other than that of being directly
apprehended by us or that of being thought of by us. This seems to me
to be often what is meant when people say that they are "immediately
experienced" or are "subjective modifications"; though, of course,
both expressions are so ambiguous, that when people say that a given
entity is immediately experienced or is a subjective modification, they
_may_ mean merely that it is directly apprehended. And since I think
this view is held, I want to explain that I see no reason whatever for
thinking that sensibles ever are experienced by us in any other sense
than that of being directly apprehended by us. Two kinds of argument,
I think, are sometimes used to show that they are.
(_a_) It is a familiar fact that, when, for instance, we are in a room
with a ticking clock, we may seem suddenly to become aware of the
ticks, whereas, so far as we can tell, we had previously not heard
them at all. And it may be urged that in these cases, since the same
kind of stimulus was acting on our ears all the time, we must have
_experienced_ the same kind of sensible sounds, although we did not
directly apprehend them.
But I think most psychologists are now agreed that this argument is
quite worthless. There seem to me to be two possible alternatives to
the conclusion drawn. It may, I think, possibly be the case that we
did directly apprehend the ticks all the time, but that we cannot
afterwards remember that we did, because the degree of attention (if
any) with which we heard them was so small, that in ordinary life we
should say that we did not attend to them at all. But, what, I think,
is much more likely is that, though the same stimulus was acting on
our ears, it failed to produce any mental effect whatever, because our
attention was otherwise engaged.
(_b_) It is said that sometimes when we suddenly become aware, say,
of the eighth stroke of a striking clock, we can _remember_ earlier
strokes, although we seem to ourselves _not_ to have directly
apprehended them. I cannot say that I have ever noticed this experience
in myself, but I have no doubt that it is possible. And people seem
inclined to argue that, since we can remember the earlier strokes, we
must have experienced them, though we did not directly apprehend them.
But here again, the argument does not seem to me at all conclusive. I
should say, again, that it is possible that we did directly apprehend
them, but only with a very slight degree of attention (if any). And,
as an alternative, I should urge that there is no reason why we should
not be able to remember a thing, which we never experienced at all.
I do not know what other arguments can be used to show that we
sometimes _experience_ sensibles in a sense quite other than that of
directly apprehending them. But I do not know how to show that we do
not; and since people whose judgment I respect, seem to hold that we
do, I think it is worth while to say something as to what this sense of
"experience" can be, in case it does occur.
I have said that sometimes when people say that a given entity is
"experienced" they seem to mean that it belongs to some individual,
in the sense in which my acts of belief belong to me. To say that
sensibles were experienced by me in this sense would, therefore, be to
say that they sometimes have to my acts of belief and acts of direct
apprehension the same relation which these have to one another--the
relation which constitutes them _mine._ But that sensibles ever have
this kind of relation to my mental acts, is a thing which I cannot
believe. Those who hold that they are ever experienced at all, in some
sense other than that of being directly apprehended, always hold, I
think, that, whenever they are directly apprehended by us, they also,
at the same time, have to us this other relation as well. And it seems
to me pretty clear that when I do directly apprehend a sensible, it
does _not_ have to me the same relation which my direct apprehension of
it has.
If, therefore, sensibles are ever experienced by us at all, in any
sense other than that of being directly apprehended by us, we must, I
think, hold that they are so in an entirely new sense, quite different
both from that in which to be experienced means to be directly
apprehended, and from that in which to be experienced means to occur
in some individual's mind. And I can only say that I see no reason to
think that they ever are experienced in any such sense. If they are,
the fact that they are so is presumably open to the inspection of us
all; but I cannot distinguish any such fact as occurring in myself, as
I can distinguish the fact that they are directly apprehended. On the
other hand, I see no way of showing that they are _not_ experienced in
some such sense; and perhaps somebody will be able to point it out to
me. I do not wish to assume, therefore, that there _is_ no such sense;
and hence, though I am inclined to think that the _only_ sense in which
they are experienced is that of being directly apprehended, I shall, in
what follows, use the phrase "experienced" to mean _either_ directly
apprehended _or_ having to something this supposed different relation,
if such a relation there be.
(3) We may now, therefore, raise the question: Do sensibles ever exist
at times when they are not being experienced at all?
To this question it is usual to give a negative answer, and two
different _a priori_ reasons may be urged in favour of that answer.
The first is what should be meant by Berkeley's dictum that the _esse_
of sensibles is _percipi._ This should mean, whatever else it may mean,
at least this: that to suppose a sensible to exist and yet _not_ to
be experienced in self-contradictory. And this at least seems to me
to be clearly false. Anything which was a patch of colour would be a
sensible; and to suppose that there are patches of colour which are not
being experienced is clearly not self-contradictory, however false it
may be.
It may, however, be urged (and this is the second argument) that,
though to suppose a thing to be a sensible and _yet_ not experienced is
not self-contradictory, yet we can clearly see that nothing can have
the one property without having the other. And I do not see my way to
deny that we may be able to know, _a priori_ that such a connection
holds between two such properties. In the present case, however, I
cannot see that it does hold, and therefore, so far as _a priori_
reasons go, I conclude that there is no reason why sensibles should not
exist at times when they are not experienced.
It may, however, be asked: Is there any reason to suppose that they
ever do? And the reason, which weighs with me most, is one which
applies, I think, to a certain class of sensibles _only_; a class
which I will try to define by saying that it consists of those which
_would_ (under certain conditions which actually exist) be experienced
in a _sensation proper, if only_ a living body, having a certain
constitution, existed under those conditions in a position in which no
such body does actually exist. I think it is very probable that this
definition does not define at all accurately the kind of sensibles I
mean; but I think that what the definition aims at will become clearer
when I proceed to give my reasons for supposing that sensibles, of a
kind to be defined in _some_ such way, do exist unexperienced. The
reason is simply that, in Hume's phrase, I have "a strong propensity
to believe" that, _e.g.,_ the visual sensibles which I directly
apprehend in looking at this paper, still exist unchanged when I merely
alter the position of my body by turning away my head or closing my
eyes, _provided_ that the physical conditions outside my body remain
unchanged. In such a case it is certainly true in some sense that I
_should_ see sensibles like what I saw the moment before, _if only_
my head were still in the position it was at that moment or my eyes
unclosed. But if, in such a case, there is reason to think that
sensibles which I should see, if the position of my body were altered,
exist in spite of the fact that I do not experience them, there is,
I think, an equal reason to suppose it in other cases. We must, for
instance, suppose that the sensibles which I should see now, if I were
at the other end of the room, or if I were looking under the table,
exist at this moment, though they are not being experienced. And
similarly we must suppose that the sensibles which _you_ would see, if
you were in the position in which I am now, exist at this moment, in
spite of the fact that they may be more or less different from those
which I see, owing to the different constitution of our bodies. All
this implies of course, that a vast number of sensibles exist at any
moment, which are not being experienced at all. But still it implies
this only with regard to sensibles of a strictly limited class, namely
sensibles which would be experienced _in a sensation proper,_ if a
body, having a certain constitution, were in a position in which it is
not, under the given physical conditions. It does not, for instance,
imply that any _images,_ of which it may be true that I _should_
have them, under present physical conditions, if the position of my
body were altered, exist now; nor does it imply that sensibles which
_would_ be experienced by me now in a sensation proper, if the physical
conditions external to my body were different from what they are, exist
now.
I feel, of course, that I have only succeeded in defining miserably
vaguely the kind of sensibles I mean; and I do not know whether the
fact that I have a strong propensity to believe that sensibles of a
kind to be defined in some such way, do exist unexperienced, is any
good reason for supposing that they actually do. The belief may, of
course, be a mere prejudice. But I do not know of any certain test by
which prejudices can be distinguished from reasonable beliefs. And I
cannot help thinking that there may be a class of sensibles, capable
of definition in _some_ such way, which there really is reason to
think exist unexperienced.
But, if I am not mistaken, there is an empirical argument which,
though, even if it were sound, it would have no tendency whatever to
show that _no_ sensibles exist unexperienced, would, if it were sound,
show that this very class of sensibles, to which alone my argument for
unexperienced existence applies, certainly do not so exist. This, it
seems to me, is the most weighty argument which can be used upon the
subject; and I want, therefore, to give my reasons for thinking that it
is fallacious.
The argument is one which asserts that there is abundant empirical
evidence in favour of the view that the existence of the sensibles
which we experience at any time, always depends upon the condition of
our nervous system: so that, even where it also depends upon external
physical conditions, we can safely say that sensibles, which we should
have experienced, if only our nervous system had been in a different
condition, certainly do not exist, when it is not in that condition.
And the fallacy of this argument seems to me to lie in the fact that
it does not distinguish between the existence of the sensibles _which_
we experience and _the fact that we experience them._ What there _is_
evidence for is that _our experience_ of sensibles always depends upon
the condition of our nervous system; that, according as the condition
of the nervous system changes, different sensibles are _experienced_,
even where other conditions are the same. But obviously the fact that
our experience of a given sensible depends upon the condition of our
nervous system does not directly show that the existence of _the
sensible experienced_ always also so depends. The fact that I am now
experiencing this black mark is certainly a different fact from the
fact that this black mark now exists. And hence the evidence which
does tend to show that the former fact would not have existed if my
nervous system had been in a different condition, has no tendency to
show that the latter would not have done so either. I am sure that this
distinction ought to be made; and hence, though I think there may be
other reasons for thinking that the very existence of the sensibles,
which we experience, and not merely the fact that we experience them
_does_ always depend upon the condition of our nervous systems, it
seems to me certain that this particular argument constitutes no such
reason.
And I think that those who suppose that it does are apt to be
influenced by an assumption, for which also, so far as I can see,
there is no reason. I have admitted that the only reason I can see for
supposing that sensibles which we experience ever exist unexperienced,
seems to lead to the conclusion that the sensibles which would be seen
by a colour-blind man, if he occupied exactly the position which I, who
am not colour-blind, now occupy, exist now, just as much as those which
I now see. And it may be thought that this implies that the sensibles,
which he would see, and which would certainly be very different from
those which I see, are nevertheless at this moment in exactly the same
place as those which I see. Now, for my part, I am not prepared to
admit that it is impossible they should be in the same place. But the
assumption against which I wish to protest, is the assumption that,
if they exist at all, they _must_ be in the same place. I can see no
reason whatever for this assumption. And hence any difficulties there
may be in the way of supposing that they could be in the same place at
the same time as the sensibles which I see, do not at all apply to my
hypothesis, which is only that they exist _now, not_ that they exist
_in the same place_ in which mine do.
On this question, therefore, as to whether sensibles ever exist at
times when they are not experienced, I have only to say (1) that I
think there is certainly no good reason whatever for asserting that
_no_ sensibles do; and (2) that I think perhaps a certain amount of
weight ought to be attached to our instinctive belief that certain
kinds of sensibles do; and that here again any special arguments which
may be brought forward to show that, whether some sensibles exist
unexperienced or not, _this_ kind certainly do not, are, so far as I
can see, wholly inconclusive.
(II)
I now pass to the question how sensibles are related to physical
objects. And here I want to say, to begin with, that I feel extremely
puzzled about the whole subject. I find it extremely difficult to
distinguish clearly from one another the different considerations which
ought to be distinguished; and all I can do is to raise, more or less
vaguely, certain questions as to how certain _particular_ sensibles
are related to certain _particular_ physical objects, and to give
the reasons which seem to me to have most weight for answering these
questions in one way rather than another. I feel that all that I can
say is very tentative.
To begin with, I do not know how "physical object" is to be defined,
and I shall not try to define it. I shall, instead, consider certain
propositions, which everybody will admit to be propositions _about_
physical objects, and which I shall assume that I know to be true.
And the question I shall raise is as to how these propositions are to
be interpreted_--in what sense_ they are true; in considering which,
we shall at the same time consider how they are related to certain
sensibles.
I am looking at two coins, one of which is a half-crown, the other a
florin. Both are lying on the ground; and they are situated obliquely
to my line of sight, so that the visual sensibles which I directly
apprehend in looking at them are visibly elliptical, and not even
approximately circular. Moreover, the half-crown is so much farther
from me than the florin that _its_ visual sensible is visibly smaller
than that of the florin.
In these circumstances I am going to assume that I know the following
propositions to be true; and no one, I think, will deny that we can
know such propositions to be true, though, as we shall see, extremely
different views may be taken as to what they mean. I know (_a_) that,
in the ordinary sense of the word "see" I am _really seeing two coins;_
an assertion which includes, if it is not identical with, the assertion
that the visual experiences, which consist in my direct apprehension
of those two elliptical patches of colour, _are_ sensations proper,
and are not either hallucinations nor mere experiences of "images";
(_b_) that the upper sides of the coins are _really_ approximately
circular, and not merely elliptical like the visual sensibles; (_c_)
that the coins _have_ another side, and an inside, though I don't see
it; (_d_) that the upper side of the half-crown is really _larger_
than that of the florin, though its visual sensible is _smaller_ than
the visual sensible of the upper side of the florin: (_e_) that both
coins continue to exist, even when I turn away my head or shut my eyes;
but in saying this, I do not, of course, mean to say that there is
absolutely _no_ change in them; I daresay there must be _some_ change,
and I do not know how to define exactly what I do mean. But we can, I
think, say at least this: viz., that propositions (_h_), (_c_), and
(_d_) will still be true, although proposition (_a_) has ceased to be
true.
Now all these propositions are, I think, typical propositions of the
sort which we call propositions about physical objects; and the two
coins themselves _are_ physical objects, if anything is. My question
is: _In what sense_ are these propositions true?
And in considering this question, there are, I think, two principles
which we can lay down as certain to begin with; though they do not
carry us very far.
The one is (_a_) that the upper side of the coin, which I am said
to _see,_ is not simply identical with the visual sensible which I
_directly apprehend_ in seeing it. That this is so might be thought to
follow absolutely from each of the two facts which I have called (_b_)
and (_d_); but I am not quite sure that it does follow from either of
these or from both together: for it seems to me just possible that the
two sensibles in question, though _not_ circular _in my private space,_
may yet be circular in _physical_ space; and similarly that though the
sensible of the half-crown is smaller than that of the florin _in my
private space,_ it may be larger _in physical space._ But what I think
it does follow from is the fact that another person may be seeing the
upper side of the coin in exactly the same sense in which I am seeing
it, and yet his sensible be certainly different from mine. From this it
follows absolutely that the upper side of the coin cannot be identical
with _both_ sensibles, since they are _not_ identical with one another.
And though it does not follow absolutely that it may not be identical
with _one_ of the two, yet it does follow that we _can_ get a case in
which it is not identical with _mine_ and I need only assume that the
case I am taking is such a case.
From this it follows that we must distinguish that sense of the word
"see" in which we can be said to "see" a physical object, from that
sense of the word in which "see" means merely to directly apprehend
a visual sensible. In a proposition of the form "I see A," where A
is a name or description of some physical object, though, if this
proposition is to be true, there must be some visual sensible, B,
which I am directly apprehending, yet the proposition "I see A" is
certainly not always, and probably never, identical in meaning with the
proposition "I directly apprehend B." In asserting "I see A" we are
asserting not only that we directly apprehend some sensible but also
something else about this sensible--it may be only some proposition of
the form, "and this sensible has certain other properties," or it may
be some proposition of the form "and _I know_ this sensible to have
certain other properties." Indeed we have not only to distinguish that
sense of the word "perceive" in which it is equivalent to "directly
apprehend," from _one_ sense in which we can be said to perceive a
physical object; we have also to distinguish at least two different
senses in which we can be said to perceive physical objects, different
both from one another and from "directly apprehend." For it is obvious
that though I should be said to be now seeing _the half-crown_, there
is a narrower, and more proper, sense, in which I can only be said
to _see_ one side of it_--not_ its lower side or its inside, and not
therefore the whole half-crown.
The other principle, which we can lay down to start with is (_β_) that
my knowledge of all the five propositions (_a_) to (_e_), is based,
in the last resort, on experiences of mine consisting in the direct
apprehension of sensibles and in the perception of relations between
directly apprehended sensibles. It is _based_ on these, in at least
this sense, that I should never have known any of these propositions
if I had never directly apprehended any sensibles nor perceived any
relations between them.
What, in view of these two principles, can be the sense in which my
five propositions are true?
(1) It seems to me possible that the only _true_ interpretation which
can be given to any of them is an interpretation of a kind which I
can only indicate rather vaguely as follows: Namely, that all of them
express only a kind of fact which we should naturally express by saying
that, _if_ certain conditions were fulfilled, I or some other person,
_should_ directly apprehend certain other sensibles. For instance
the only _true_ thing that can be meant by saying that I really see
_coins_ may be some such thing as that, _if_ I were to move my body in
certain ways, I should directly apprehend _other_ sensibles, _e.g._
tactual ones, which I should not directly apprehend as a consequence
of these movements, if these present visual experiences of mine were
mere hallucinations or experiences of "images." Again, the only true
thing that can be meant by saying that the upper sides of the coins
are _really_ approximately circular may be some such thing as that,
_if_ I were looking straight at them, I should directly apprehend
circular sensibles. And similarly, the only true interpretation of
(_c_) may be some such fact as that, _if_ I were to turn the coins
over, or break them up, I _should_ have certain sensations, of a sort I
can imagine very well; of (_d_) that _if_ I were at an equal distance
from the half-crown and the florin, the sensible, I should then see
corresponding to the half-crown would be bigger than that corresponding
to the florin, whereas it is now smaller; of (_e_) that, _if,_ when
my eyes were closed, they had been open instead, I should have seen
certain sensibles.
It is obvious, indeed, that if any interpretation on these lines _is_
the only true interpretation of our five propositions, none of those
which I have vaguely suggested comes anywhere near to expressing it in
its ultimate form. They cannot do so for the simple reason that, in
them, the conditions under which I _should_ experience certain other
sensibles are themselves expressed in terms of _physical objects,_ and
not in terms of sensibles and our experience of them. The conditions
are expressed in such terms as "if I were to move my body," "if I
were to look straight at the coins," "if I were to turn the coins
over," etc.; and all these are obviously propositions, which must
themselves again be interpreted in terms of sensibles, if our original
five propositions need to be so. It is obvious, therefore, that any
_ultimate_ interpretation of our five propositions, on these lines,
would be immensely complicated; and I cannot come anywhere near to
stating exactly what it would be. But it seems to me possible that
_some_ such interpretation could be found, and that it is the _only_
true one.
The great recommendation of this view seems to me to be that it enables
us to see, more clearly than any other view can, how our knowledge of
physical propositions can be based on our experience of sensibles, in
the way in which principle (_β_) asserts it to be. If, when I know
that the coins are round, all that I know is some such thing as that
if, after experiencing the sensibles I do now experience, I were to
experience still others, I should finally experience a third set, we
can understand, as clearly as we can understand how any knowledge can
be obtained by induction at all, how such a knowledge could be based on
our previous experience of sensibles, and how it could be verified by
our subsequent experience.
On the other hand, apart from the difficulty of actually giving any
interpretation on these lines, which will meet the requirements,
the great objection to it seems to me to be this. It is obvious
that, on this view, though we shall still be allowed to say that the
coins _existed_ before I saw them, are _circular_ etc., all these
expressions, if they are to be true, will have to be understood in a
Pickwickian sense. When I know that the coins existed before I saw
them, what I know will not be that anything whatever existed at that
time, in the sense in which those elliptical patches of colour exist
now. _All_ that I know will be simply that, since the elliptical
patches exist now, it is true, that, _if_ certain unrealised conditions
had been realised, I should have had certain sensations that I have
not had; or, _if_ certain conditions, which may or may not be realised
in the future, were to be so, I _should_ have certain experiences.
Something like this will actually be the _only true_ thing that can
be meant by saying that the coins existed before I saw them. In
other words, to say of a _physical object_ that it _existed_ at a
given time will always consist merely in saying of some sensible,
_not_ that _it_ existed at the time in question, but something quite
different and immensely complicated. And thus, though, when I know that
the coins exist, what I know will be merely some proposition about
these sensibles which I am directly apprehending, yet this view will
not contradict principle (_a_) by _identifying_ the coins with the
sensibles. For it will say that to assert a given thing of the _coins_
is not equivalent to asserting the _same thing_ of the sensibles, but
only to asserting of them something quite different.
The fact that these assertions that the coins exist, are round, etc.,
will, on this view, only be true in this outrageously Pickwickian
sense, seems to me to constitute the great objection to it. But it
seems to me to be an objection only, so far as I can see, because I
have a "strong propensity to believe" that, when I know that the coins
existed before I saw them, _what_ I know is that something existed at
that time, in the very same sense in which those elliptical patches now
exist. And, of course, this belief _may_ be a mere prejudice. It _may_
be that when I believe that I _now_ have, in my body, blood and nerves
and brain, _what_ I believe is only true, if it does _not_ assert, in
the proper sense of the word "existence," the _present_ existence of
anything whatever, other than sensibles which I directly apprehend, but
only makes assertions as to the kind of experiences a doctor _would_
have, if he dissected me. But I cannot feel at all sure that my belief,
that, when I know of the present Existence of these things (as I think
I do), I am knowing of the present existence (in the proper sense) of
things other than any sensibles which I or any one else am now directly
apprehending, is a mere prejudice. And therefore I think it is worth
while to consider what, if it is not, these things, of whose existence
I know, can be.
(2) It is certain that if, when I know that that half-crown existed
before I saw it, I am knowing that something existed at that time
in other than a Pickwickian sense, I only know this something _by
description_; and it seems pretty clear that the description by
which I know it is as _the_ thing which has a certain connection
with this sensible which I am now directly apprehending. But _what_
connection? We cannot simply say, as many people have said, that by
"that half-crown" I mean _the_ thing which _caused_ my experience of
this sensible; because events which happen between the half-crown and
my eyes, and events in my eyes, and optic nerves, and brains are just
as much _causes_ of my experiences as the half-crown itself. But it
may perhaps be the case that the half-crown has some particular _kind_
of causal relation to my experience, which these other events have not
got--a kind which may be expressed, perhaps, by saying that it is its
"source." And hence, when I know that that half-crown is circular, I
may perhaps be knowing that the _source_ of this experience is circular.
But what sort of a thing can this "source" be?
One kind of view, which I think is very commonly held, is that it is
something "spiritual" in its nature, or something whose nature is
utterly unknown to us. And those who hold this view are apt to add,
that it is not really "circular," in any sense at all; nor is the
"source" of my half-crown experience, in any sense at all, "bigger"
than that of my florin experience. But if this addition were seriously
meant, it would, of course, amount to saying that propositions (_b_)
and (_d_) are not true, in any sense at all; and I do not think
that those who make it, really mean to say this. I think that what
they mean is only that the only sense in which those "sources" are
circular, and one bigger than the other, is one in which to say this
merely amounts to saying that the sensibles, which they _would_ cause
us to experience, under certain conditions, _would_ be circular, and
one bigger than the other. In other words, in order to give a true
interpretation to the propositions that the coins are circular and one
bigger than the other, they say that we must interpret them in the same
kind of way in which view (1) interpreted them; and the only difference
between their view and view (1), is that, whereas _that_ said that you
must give a Pickwickian interpretation _both_ to the assertion that the
coins _exist, and_ to the assertion that they are _circular_, they say
that you must _not_ give it to the former assertion, and must to the
latter.
To this view my objection is only that any reason there may be for
saying that the "sources" exist in other than a Pickwickian sense,
seems to me to be also a reason for saying that they are "circular" in
a sense that is not Pickwickian. I have just as strong a propensity to
believe that they are really circular, in a simple and natural sense,
as that they exist in such a sense: and I know of no better reason for
believing either.
(3) It may be suggested, next, that these "sources," instead of being
something spiritual in their nature or something of a nature utterly
unknown, consist simply of sensibles, of a kind which I have previously
tried to define; namely of all those sensibles, which anybody _would,_
under the actual physical conditions, experience in _sensations proper_
of which the half-crown and the florin were the source, _if_ their
bodies were in any of the positions relatively to those coins, in which
they would get sensations from them at all. We saw before that it seems
_possible_ that all these sensibles do really exist at times when they
are not experienced, and that some people, at all events, seem to have
a strong propensity to believe that they do. And in favour of the view
that some such huge collection of sensibles _is_ the upper side of the
half-crown, is the fact that we do seem to have a strong propensity
to believe that any particular sensible, which we directly apprehend
in looking at the upper side of the half-crown, and of our direct
apprehension of which the upper side is the source, is _in the place_
in which the upper side is. And that _some_ sense might be given to
the expression "in the same place as," in which it could be true that
sensibles of all sorts of different shapes and sizes, and of all sorts
of different colours, were in the same place at the same time, seems to
me to be possible. But the objection to this view seems to me to be the
same as to the last; namely that if the upper side of the half-crown
were identical with such a collection of sensibles, then the only sense
in which it could be said to be "circular," or bigger than that of the
florin, would certainly be very Pickwickian, though not the same as on
that view.
(4) If, for the reasons given, we reject both (1), (2), and (3) as
interpretations of our five propositions, the only alternative I
can think of that remains, is one which is roughly identical, so far
as I can see, with Locke's view. It is a view which asserts that the
half-crown and the florin really did exist (in the natural sense)
before I saw them; that they really are approximately circular (again
in the natural sense); that, therefore, they are not composed of
sensibles which I or others should directly apprehend under other
conditions; and that therefore also neither these sensibles (even if
such do now exist) nor those which I am now directly apprehending are
in the place in which the coins are. It holds, therefore, that the
coins do really _resemble_ some sensibles, in respect of the "primary"
qualities which these have; that they really are round, and one larger
than the other, in much the same sense in which some sensibles are
round and some larger than others. But it holds also that no sensibles
which we ever do directly apprehend, or should directly apprehend, if
at a given time we were in other positions, are _parts_ of those coins;
and that, therefore, there is no reason to suppose that any parts of
the coins have any of the "secondary qualities"--colour, etc.--which
any of these sensibles have.
On this view, it is plain, there is nothing to prevent us from holding
that, as suggested in I (3), all sorts of unexperienced sensibles do
exist. We are only prevented from holding that, if they do, those which
have the same source all exist in the _same place_ as their source.
And the natural view to take as to the status of sensibles generally,
relatively to physical objects, would be that none of them, whether
experienced or not, were ever in the same place as any physical object.
That none, therefore, exist "anywhere" in physical space; while, at the
same time, we can also say, as argued in I (2), that none exist "in the
mind," except in the sense that some are directly apprehended by some
minds. And the only thing that would need to be added, is that some,
and some only, _resemble_ the physical objects which are their source,
in respect of their shape.
To this view I can see no objection except the serious one that it
is difficult to answer the questions: How can I ever come to know
that these sensibles have a "source" at all? And how do I know that
these "sources" are circular? It would seem that, if I do know these
things at all, I must know _immediately_, in the case of _some_
sensibles, both that they have a source and what the shape of this
source is. And to this it may be objected that this is a kind of thing
which I certainly cannot know immediately. The argument in favour
of an interpretation of type (i) seems to me to rest wholly on the
assumption that there are only certain kinds of facts which I can know
immediately; and hence that if I believe I know a fact, which is not of
this kind, and which also I cannot have learnt immediately, my belief
must be a mere prejudice. But I do not know how it can be shown that an
assertion of the form: Facts of certain kinds are the only ones you can
know immediately; is itself not a prejudice. I do not think, therefore,
that the fact that, if this last view were true, we should have to
admit that we know immediately facts of a kind which many people think
we cannot know immediately, is a conclusive objection to it.