apt to be overlooked. It may, perhaps, be allowed that observation
gives some reason for the proposition that hens' eggs are generally
laid by hens. I do not mean to say that any one man's observation can
give a reason for this proposition: I do not assume either that it can
or that it cannot. Nor do I mean to make any assumption as to what
must be meant by the words "hens" and "eggs," if this proposition is
to be true. I am quite willing to allow for the moment that if it is
true at all, we must understand by "hens" and "eggs," objects very
unlike that which we directly observe, when we see a hen in a yard, or
an egg on the breakfast-table. I am willing to allow the possibility
that, as some Idealists would say, the proposition "Hens lay eggs" is
false, unless we mean by it: A certain kind of collection of spirits or
monads sometimes has a certain intelligible relation to another kind of
collection of spirits or monads. I am willing to allow the possibility
that, as Reid and some scientists would say, the proposition "Hens
lay eggs" is false, if we mean by it anything more than that: Certain
configurations of invisible material particles sometimes have a certain
spatio-temporal relation to another kind of configuration of invisible
material particles. Or again I am willing to allow, with certain
other philosophers, that we must, if it is to be true, interpret
this proposition as meaning that certain kinds of sensations have to
certain other kinds a relation which may be expressed by saying that
the one kind of sensations "lay" the other kind. Or again, as other
philosophers say, the proposition "Hens lay eggs" may possibly mean:
Certain sensations of mine _would_, under certain conditions, have to
certain other sensations of mine a relation which may be expressed by
saying that the one set would "lay" the other set. But whatever the
proposition "Hens' eggs are generally laid by hens" may _mean_, most
philosophers would, I think, allow that, in some sense or other, this
proposition was true. And they would also I think allow that we have
_some_ reason for it; and that _part_ of this reason at all events lies
in observation: they would allow that we should have no reason for it
unless certain things had been observed, which have been observed.
Few, I think, would say that the existence of an egg "intrinsically
points" to that of a hen, in such a sense that, even if we had had no
experience of any kind concerning the manner in which objects like eggs
are connected with animals like hens, the mere inspection of an egg
would justify the assertion: A hen has probably existed.
I assume, then, that objects having all the characteristics which
hens' eggs have (whatever these may be) are generally laid by hens
(whatever hens may be); and I assume that, if we have any reason
for this generalisation at all, observation gives us some reason
for it. But now, let us suppose that the only observations we had
made were those which we should commonly describe by saying that we
had seen a hen laying an egg. I do not say that any number of such
observations, by themselves, would be _sufficient_ to justify our
generalisation: I think it is plain that they would not. But let us
suppose, for the moment, that we had observed nothing else which bore
upon the connection between hens and eggs; and that, if therefore
our generalisation was justified by any observations at all, it was
justified by these. We are supposing, then, that the observations
which we describe as "seeing hens lay eggs" give some reason for the
generalisation that eggs of that kind are generally laid by hens. And
if these observations give reason for this, obviously _in a sense_
they give reason for the generalisation that the existence of such an
egg is generally preceded by that of a hen; and hence also, they give
us reason to suppose that if such an egg exists, a hen has probably
existed also--that unless a hen had existed, the egg would not have
existed. But the point to which I wish to call attention is that it
is _only_ in a limited sense that they do give reason for this. They
only give us reason to suppose that, for each egg, there has existed a
hen, which was at some time _near_ the place where the egg in question
then was, and which existed at a time _near_ to that at which the egg
began to exist. The only kind of hens, whose existence they do give us
reason to suppose, are hens, of which each was at some time in spatial
and temporal proximity (or, if Idealists prefer, in the relations which
are the "intelligible counterparts" of these) to an egg. They give us
no information at all about the existence of hens (if there are any)
which never came within a thousand miles of an egg, or which were dead
a thousand years before any egg existed. That is to say, they _do_
give us reason to suppose that, if a particular egg exists, there has
probably existed a hen which was at some time _near_ that egg; but
they give us no reason to suppose that, if a particular egg exists,
there must have existed a hen which never came near that egg. They
_do_ give us reason to suppose that, for each egg, there has probably
existed a hen which at some time stood to the egg in question in that
relation which we have observed to hold between an egg and a hen, when
we observed the hen laying an egg. But they give us no reason to infer
from the existence of an egg any other kind of hen: any hen which
_never_ stood to the egg in the relation in which we have observed that
some hens do stand to eggs.
What I wish to suggest is that this condition is a universal condition
for sound inductions. If the observation of β preceding _α_ can ever
give us any reason at all for supposing that the existence of A is
generally preceded by that of B, it can at most only give us reason
to suppose that the existence of an A is generally preceded by that
of a B _which stands to our A in the same relation in which β_ has
been observed to stand to _α._ It cannot give the least reason for
supposing that the existence of an A must have been preceded by that
of a B, which did _not_ stand to A in the observed relation, but in
some quite different one. If we are to have any reason to infer from
the existence of an A the existence of such a B, the reason must lie in
some different observations. That this is so, in the case of hens' eggs
and hens, is, I think, obvious: and, if the rule is _not_ universal,
some reason should at least be given for supposing that it does apply
in one case and not in another.
Having thus attempted to point out some conditions which seem to be
necessary, though not _sufficient_, where observation is to give any
reason for a generalisation, I may now proceed to my second preliminary
question. What kinds of things do we observe?
In order to illustrate how much and how little I mean by "observation"
or "direct perception," I will take as an instance a very common
visual perception. Most of us are familiar with the experience which
we should describe by saying that we had seen a red book and a blue
book side by side upon a shelf. What exactly can we be said to observe
or directly perceive when we have such an experience? We certainly
observe one colour, which we call blue, and a different colour, which
we call red; each of these we observe as having a particular size and
shape; and we observe also these two coloured patches as having to one
another the spatial relation which we express by saying they are side
by side. All this we certainly see or directly perceive _now,_ whatever
may have been the process by which we have come to perceive so much.
But when we say, as in ordinary talk we should, that the objects we
perceive are _books,_ we certainly mean to ascribe to them properties,
which, in a sense which we all understand, are not actually seen by
us, at the moment when we are merely looking at two books on a shelf
two yards off. And all such properties I mean to exclude as not being
then _observed_ or _directly perceived_ by us. When I speak of what
we _observe,_ when we see two books on a shelf, I mean to limit the
expression to that which is _actually seen._ And, thus understood, the
expression does include colours, and the size and shape of colours, and
spatial relations in three dimensions between these patches of colour,
but it includes nothing else.
But I am also using observation in a sense in which we can be said
actually to observe a movement. We commonly say that we can sometimes
_see_ a red billiard ball moving towards a white one on a green table.
And, here again, I do not mean to include in what is directly perceived
or observed, all that we mean by saying that the two objects perceived
are billiard-balls. But I do mean to include what (we should say) we
_actually see._ We actually see a more or less round red patch moving
towards a more or less round white patch; we _see_ the stretch of green
between them diminishing in size. And this perception is not merely the
same as a series of perceptions--first a perception of a red patch with
a green stretch of one size between it and the white; then a perception
of a red patch with a green stretch of a different size between it and
the white; and so on. In order to perceive a movement we must have a
different perception from any one of these or from the sum of them. We
must _actually see_ the green stretch diminishing in size.
Now it is undoubtedly difficult, in some instances, to decide precisely
what is perceived in this sense and what is not. But I hope I have
said enough to show that I am using "perceive" and "observe" in a
sense in which, on a given occasion, it is easy to decide that _some_
things certainly are perceived, and other things, as certainly, are
not perceived. I am using it in a sense in which we do perceive such
a complex object as a white patch moving towards a red one on a green
field; but I am not using it in any sense in which we could be said to
"perceive" or "observe" that what we saw moving was a billiard-ball.
And in the same way I think we can distinguish roughly between what,
on any given occasion, we perceive, as we say, "by any one of the
other senses," and what we do not perceive by it. We can say with
certainty that, on any given occasion, there are certain kinds of
"content" which we are actually hearing, and others which we are _not_
actually hearing; though with regard to some again it is difficult to
say whether we are actually hearing them or not. And similarly we can
distinguish with certainty in some instances, between what we are on
a given occasion, actually smelling or feeling, and what we are not
actually smelling or feeling.
But now, besides these kinds of "things," "objects," or "contents,"
which we perceive, as we say, "by the senses," there is also another
kind which we can be said to observe. Not only can I observe a red and
blue book side by side; I can also observe myself observing them. I can
perceive a red patch moving towards a white, and I can also perceive my
perception of this movement. And what I wish to make as plain as I can
is that my perception of the movement of a coloured patch can at least
be distinguished from that movement itself. I wish to make it plain
that to observe a coloured patch moving is to observe one thing; and
to observe myself observing a coloured patch moving is another. When
I observe my own perception of a movement, I observe something _more_
than when I merely observe the movement, and something very different
from the movement. I may perceive a red and a blue book side by side on
a shelf; and at another time I may perceive a red ball moving towards a
white. The red and blue patch, of one shape, at rest side by side, are
different from the red, of another shape, moving towards the white; and
yet, when I say that both are "perceived," I mean by "perceived" one
and the same thing. And since, thus, two different things may both be
perceived, there must also be some difference between each of them and
what is meant by saying that it is perceived. Indeed, in precisely the
same way In which I may observe a spatial relation between a red patch
and a blue (when I observe them "side by side") I do, when I observe my
own perception of them, observe a spatial relation between it and them.
I observe a distance between my perception and the red and blue books
which I perceive, comparable in magnitude with the breadth or height
of the blue book, just as these are comparable in magnitude with one
another. And when I say I observe a distance between my perception
of a red book and that red book itself, I do not mean that I observe
a distance between my eyes, or any other part of what I call my body,
and the red patch in question. I am talking not of my eyes, but of my
actual perception. I observe my perception of a book to be near the
book and further from the table, in exactly the same sense in which I
observe the book to be near the shelf on which it stands, and further
from the table. And just as, if the distance between a red patch and
a white is to be perceived, the red patch must be different from the
white, so, if I perceive a certain distance between my perception and
the red patch, my perception must be different from the red patch which
I perceive.
I assume, then, that we observe, on the one hand, coloured patches of
certain shapes and sizes, and their spatial relations to one another,
together with all the other kinds of "contents," which we should
usually be said to perceive "through the senses." And, on the other
hand, we also sometimes observe our own perceptions of such "contents"
and our thoughts. And these two kinds of "content" are different from
one another: my perception of a red patch with gold letters on it,
is not itself a red patch with gold letters on it; and hence, when I
observe my perception of this patch, I observe something different from
that which I observe when I merely perceive the patch. Either of these
two kinds of "content"--either colours, moving or at rest, sounds,
smells, and all the rest--or, on the other hand, my perceptions of
these--either of these two kinds, or both, might conceivably, since
both are observed, give grounds for a generalisation concerning what
exists. But, as I have said, if observations are to give any ground
for such a generalisation, it must be assumed that what Is observed
_exists_ or is _real._ And since, as I have insisted, when I observe
my _perception_ of a red patch with gold letters on it, I observe
something different from what I observed when I merely observed a red
patch with gold letters on it, it follows that to assume the existence
of my perception of this red and gold is _not_ the same thing as to
assume the existence of the red and gold itself.
But what, it may be asked, do I mean by this property of "existence" or
"reality," which may, it would seem, belong to every content, which I
observe, or may again belong to none, or which may belong to some and
not to others? What is this property which may belong to my perception
of a movement, and yet not belong to the movement perceived, or which
may again belong to the movement perceived and not to my perception of
it, or which may again belong to both or to neither?
It is necessary, I think, to ask this question at this point, because
there are some philosophers who hold that, in the case of some kinds
of "content," at all events, to say that they "exist" is to say that
they are "perceived." Some hold that to say "A exists" is to say
neither more nor less than "A is perceived"--that the two expressions
are perfect synonyms; and others again would say that by "A exists
or is real" we may mean _more_ than that "A is perceived," but that
we must at least mean this. Now, I have hitherto used the word
"existence" pretty freely, and I think that, when I used it, I used
it in its ordinary sense. I think it will generally have suggested to
you precisely what I meant to convey, and I think that, in some cases
at all events, it will not even have occurred to you to doubt whether
you did understand what I meant by it. But, if these philosophers are
right, then, if you _have_ understood what I meant by it, I have all
along been using it in a sense, which renders the end of my last
paragraph perfect nonsense. If these philosophers are right, then, when
I assert that what _is_ perceived may yet _not_ exist, I am really
asserting that what _is_ perceived may yet _not_ be perceived--I am
contradicting myself. I am, of course, quite unaware that I am doing
so. But these philosophers would say _either_ you are contradicting
yourself, _or_ you are not using the word "exists" in its ordinary
sense. And either of these alternatives would be fatal to my purpose.
If I am not using the word in its ordinary sense, then I shall not be
understood by anyone; and, if I am contradicting myself, then what I
say will not be worth understanding.
Now, with one class of these philosophers--the class to which, I
think, Berkeley belongs--I think I can put myself right comparatively
easily. The philosophers I mean are those who say that it is only in
the case of one particular class of "contents" (the kind of "content"
which Berkeley calls "ideas") that to say "the 'content' A exists"
is to say "A is perceived," and who admit that in the case of other
contents--myself and my perceptions and thoughts, for example--to say
that _these_ exist or are real, is to say of them something different
from this. These philosophers admit, that is to say, that the word
"exists" has two different senses: and that in only one of these senses
is it synonymous with the words "is perceived." When (they hold) I
say of such a content as a red patch with gold letters on it that
it "exists" I _do_ mean that it is perceived; but when I say of my
_perception_ of such a patch that _it_ exists, I do _not_ mean that
my perception is perceived but something different from this. Now, it
would be nothing strange that one and the same word should be used in
two different senses; many words are used in many different senses.
But it would, I think, be something very strange indeed, if in the
case of a word which we constantly apply to all sorts of different
objects, we should uniformly apply it to one large class of object in
the one sense and the one sense only and the other large class in the
other sense and the other sense only. Usually, in the case of such
ambiguous words, it happens that, in different contexts, we apply it
to one and the same object in _both_ senses. We sometimes wish to
say of a given object that it has the one property, and sometimes we
wish to say of the same object that it has the other property; and
hence we apply the same word to the same object, at one time in one
sense, and at another in the other. I think, therefore, that, even
if there were these two different senses of the word "existence," it
would be very unlikely that we should not commonly, in some contexts,
apply it in the sense, in which (as is alleged) it does apply to
perceptions, to "contents" which are not perceptions. Indeed, I think,
it is quite plain that we constantly do ask, with regard to what is
not a perception, whether _it_ exists, in precisely the same sense,
in which we ask, with regard to a perception, whether _it_ exists. We
ask in precisely the same sense: Was the Roc a real bird, or merely an
imaginary one? and, did Sindbad's perception of the Roc really exist,
or is it a fiction that he perceived a Roc? I think, therefore, that
the sense in which these philosophers admit that we do apply the word
"existence" to perceptions, is one in which we also commonly apply it
to "contents" other than perceptions. But, even if this is not the
case, I can set myself right with them by a simple explanation. I
need merely explain that the sense in which I am proposing to enquire
whether a red patch exists, is precisely the sense in which they admit
that my perception of a red patch does exist. And in this sense, it is
plain that to suppose that a thing may exist, which is not perceived,
or that it may _not_ exist, although it is perceived, is at least not
self-contradictory.
But there may be other philosophers who will say that, in the case of
a perception also, to say that it exists or is real is to say that
it is perceived--either that alone or something more as well. And to
these philosophers I would first point out that they are admitting
that the proposition "This perception is real" is significant. There
is some sense or other in which we may say: "Alexander's perception of
an elephant was real or did exist, but Sindbad's perception of a Roc
was _not_ real--never did exist": the latter proposition is, in some
sense or other, not self-contradictory. And then I would ask of them:
When they say, that to call a perception "real" is to assert that it
is perceived, do they mean by this that to call it real is to assert
that it is _really_ perceived, or not? If they say "No," then they are
asserting that to call a perception "real" is merely to say that it was
perceived in the sense in which Sindbad _did_ perceive a Roc: they are
asserting that to call it "real" is not to say, in any sense, that it
was _really_ perceived: they are asserting that to call a perception
"real" is to say that it was perceived, in some sense quite other than
that in which we ordinarily use the word: for we certainly commonly
mean, when we say "A was perceived," that a perception of A was "real":
we should commonly say that Sindbad did _not_ perceive a Roc--meaning
that no such perception ever did exist. I do not think they do mean
this; and, in any case, if they do, I think it is plain that they
are wrong. When we say that a perception is "real," we certainly do
not mean merely that it is the object of another perception, which
may itself be quite unreal--purely Imaginary. I assume, therefore,
that when they say: To call a perception "real" is to say that it is
perceived; they mean, what we should naturally understand, namely,
that: To call it "real" is to say that it is _really_ perceived--to say
that it is the object of another perception, which is also _real_ in
the same sense. And, if they mean this, then what they say is certainly
untrue. Their definition of reality is circular. It cannot be the case
that the _only_ sense in which a perception may be said to be real, is
one in which to call it so is to assert that not it alone, but another
perception is real also. It cannot be the case that the assertion "A is
real" is _identical_ with the assertion "A and B are both real," where
A and B are different, and "real" is used in the same sense as applied
to both. If it is to be true that the assertion "A is real" _ever_, in
any sense, includes the assertion "A is _really_ perceived," there must
be another sense of the word "real," in which to assert "A is real" is
to assert _less_ than "A is _really_ perceived"--the sense, namely, in
which we here assert that the _perception_ of A is real.
We find, therefore, that the other class of philosophers were at least
right in this: they were right in allowing that the sense in which
we commonly say that our perceptions exist is one in which "exist"
does not include, even as a part of its meaning, "is perceived." We
find that there is a common sense of the word "existence," in which
to say "A exists" must mean _less_ than "A is _really_ perceived":
since, otherwise, the only possible definition of the word "existence"
would be a circular definition. And I may point out that two other
definitions, which have been sometimes suggested by philosophers as
giving what we commonly mean by "reality" or "existence" are vitiated
by the same fault--they also are circular. Some philosophers have
sometimes suggested that when we call a thing "real," we mean that it
is "systematically connected" in some way with other things. But,
when we look into their meaning, we find that what they mean is (what,
indeed, is alone plausible)--systematically connected with other
_real_ things. And it may possibly be the case that we sometimes use
the word "real" in this sense: but, at least, it must be certainly
the case, that, if we do, we _also_ use it in another and simpler
sense--the sense in which it is employed in the proposed definition.
And other philosophers have suggested that what we mean by "real"
is--"connected in some way with a purpose--helping or hindering,
or the object of a purpose." But if we look into their meaning, we
find they mean--connected with a _real_ purpose. And hence, even if
we do sometimes mean by "real," "connected with a _real_ purpose,"
it is plain we also sometimes mean by "real" something simpler than
this--that namely, which is meant by "real" in the proposed definition.
It is certain, therefore, that we do commonly use the word "existence"
in a sense, in which to say "A exists" is _not_ to say "A is
perceived," or "A is systematically connected with other real things,"
or "A is purposive." There is a simpler sense than any of these--the
sense in which we say that our own perceptions do exist, and that
Sindbad's perceptions did not exist. But when I say this, I am by no
means denying that what exists, in this simple sense, may not always
_also_ exist in all the others; and that what exists in any of them
may not _also_ always exist in this. It is quite possible that what
exists is always _also_ perceived, and that what is perceived always
_also_ exists. All that I am saying is that, even if this is so, this
proposition is significant--is not merely a proposition about the
meaning of a word. It is not self-contradictory to suppose that some
things which exist are not perceived, and that some things which are
perceived do not exist.
But, it may be asked: What is this common simple sense of the word
"exists"? For my own part, it seems to me to be so simple that it
cannot be expressed in other words, except those which are recognised
as its synonyms. I think we are all perfectly familiar with its
meaning: it is the meaning which you understood me to have throughout
this paper, until I began this discussion. I think we can perceive at
once what is meant by asserting that my perception of black marks on a
white ground is "real," and that no such perception as Sindbad's of a
Roc was ever "real": we are perfectly familiar with the property which
the one perception is affirmed to possess, and the other to be without.
And I think, as I have said, that this property is a simple one. But,
whatever it is, this, which we ordinarily mean, is what I mean by
"existence" or "reality." And this property, we have seen, is certainly
neither identical with nor inclusive of that complex one which we mean
by the words "is perceived."
I may now, then, at last approach the main question of my paper.
Which among the "contents" which I observe will give me reason to
suppose that my observation of some of them is generally preceded
or accompanied or followed by the existence of certain particular
perceptions, thoughts or feelings in another person? I have explained
that the "contents" which I actually observe may be divided into two
classes: on the one hand, those which, as we commonly say, we perceive
"through the senses"; and, on the other hand, my perceptions of these
last, my thoughts, and my feelings. I have explained that if any
of these observed contents are to give reason for a generalisation
about what exists, _they_ must exist. And I have explained that with
regard to both classes of "contents" I am using the word "exist" in
precisely the same sense--a sense, in which it is certainly not
self-contradictory to suppose that what _is_ perceived, does not exist,
and that what is _not_ perceived, does exist; and, in which, therefore,
the assumption that a red patch with gold letters on it exists, is a
_different_ assumption from the assumption that my _perception_ of
a red patch with gold letters on it exists; and the assumption that
my _perception_ of a red patch with gold letters on it exists, is a
_different_ assumption from the assumption that a red patch with gold
letters on it exists.
What, then, that we observe, can give us any reason for believing that
anyone else has certain particular perceptions, thoughts or feelings?
It has, I think, been very commonly assumed that the observation of
my own perceptions, thoughts, and feelings, can, by itself, give me
such a reason. And I propose, therefore, to examine this assumption.
If, as I hope to show, it is false; it will then follow, that if our
own observation gives us any reason whatever, for believing in the
existence of other persons, we must assume the existence, not only
of our own perceptions, thoughts and feelings, but also of some, at
least, among that other class of data, which I may now, for the sake of
brevity, call "sense-contents"; we must assume that some of them exist,
in precisely the same sense in which we assume that our perceptions,
thoughts, and feelings exist.
The theory which I propose to examine is, then, the following. My
observation of my own thoughts, feelings, and perceptions may, it
asserts, give me some reason to suppose that another person has
thoughts, feelings, and perceptions similar to some of mine. Let us
assume, accordingly, that my own thoughts, feelings, and perceptions
do exist; but that none of the "sense-contents," which I also observe,
do so. Where among my perceptions am I to look for any which might
conceivably give me a reason for supposing the existence of other
perceptions similar to my own? It is obvious where I must look. I have
perceptions which I call perceptions of other people's bodies; and
these are certainly similar in many respects to other perceptions of
my own body. But I also observe that certain kinds of perceptions of
my own body are preceded by certain other perceptions, thoughts, or
feelings of mine. I may, for instance, observe that when I perceive
my hand suddenly catch hold of my foot in a particular way, this
perception was preceded by a particular kind of feeling of pain. I
may, perhaps, observe this often enough to justify the generalisation
that the perception of that particular motion of my body is generally
preceded by that particular feeling of pain. And in this way I may
perhaps have reason for quite a number of generalisations which assert
that particular kinds of perceptions of my own body are generally
preceded by other particular kinds of perceptions, thoughts, or
feelings of my own.
But I may also, no doubt, have the perception, which I call the
perception of another person's hand catching hold of his foot, in a
manner similar to that in which I have perceived my own hand catch
hold of my own foot. And my perception of another person's hand
catching hold of his foot may undoubtedly be similar in many respects
to my perception of my own hand catching hold of my own foot. But
I shall not observe the same kind of feeling of pain preceding my
perception of _his_ hand catching hold of his foot, which I have
observed preceding my perception of _my_ hand catching hold of my
foot. Will my generalisation, then, give me any reason to suppose
that nevertheless my perception of his hand catching hold of his foot
_is_ preceded by a similar feeling of pain, not in me but in him?
We undoubtedly do assume that when I perceive another person's body
making movements similar to those which I have observed my own body
making, this perception has generally been preceded by some feeling or
perception of his similar to that which I have observed to precede my
perception of similar movements in my own body. We do assume this; and
it is precisely the kind of generalisation, which, I have insisted,
must be admitted to be true. But my present question is: Will such
observations as I have described give any reason for thinking any
such generalisation true? I think it is plain that they will not give
the slightest reason for thinking so. In the first place, all the
perceptions which I call perceptions of another person's body differ
very considerably from any of those which I call perceptions of my
own. But I am willing to waive this objection. I am not offering any
theory as to what degree of likeness is _sufficient_ to justify a
generalisation: and therefore I will allow that the degree of likeness
_may_ be sufficient. But there remains an objection which is, I think,
quite fatal to the proposed inference. This objection is that the
inference in question plainly does not satisfy the third condition
which I suggested above as _necessary_, wherever any generalisation
is to be justified by observation. I am willing to allow that my
observations of the fact that my perception of a certain movement in
my own body is preceded by a certain feeling of pain, _will_ justify
the generalisation that my perception of any such movement, whether in
my own body _or_ in that of another person, is generally preceded by a
similar feeling of pain. And I allow, therefore, that when I perceive a
certain movement in another's body, it _is_ probable that the feeling
of pain exists, though I do not perceive it. But, if it _is_ probable
that such a feeling of pain exists, such a feeling must stand _in the
same relation_ to my perception of the movement in another person's
body, in which a similar feeling of pain has been observed by me to
stand to my perception of such a movement in my own body. That is to
say the only kind of feeling of pain, which my observations do justify
me in inferring, if (as I admit they may) they justify me in inferring
any at all, is a feeling of pain of _my own._ They cannot possibly
justify the belief in the existence of any such feeling _except_ one
which stands to my perception in the same relation in which my feelings
do stand to _my_ perceptions--one, that is to say, which is my own. I
have no more reason to believe that the feeling of pain which probably
precedes my perception of a movement in another person's body can be
the feeling _of another person_, than, in my former example, I had
reason to suppose that the hen, whose existence probably preceded that
of a given egg, could be a hen, which had never been near the egg in
question. The two cases are exactly analogous. I observe a feeling of
pain _of my own_ preceding a perception _of my own._ I observe the
two, that is to say, as standing to one another, in those relations
(whatever they may be) in which any perception of mine stands to any
other thought, perception or feeling of mine, and which are, at all
events, different from any relation in which a perception or feeling of
another person can stand to one of mine. I never perceive the feeling
and the perception as standing in any other relation. In any case,
therefore, where I do observe something like the perception, but do
not observe the feeling, I can only be justified (_if_ justified in
inferring any feeling at all), in inferring an unperceived feeling _of
my own._
For this reason I think that no observations of my own perceptions,
feelings or thoughts can give me the slightest reason for supposing a
connection between any of them and any feeling, perception, or thought
in another person. The argument is perfectly general, since _all_
my perceptions, feelings and thoughts do have to one another those
relations in virtue of which I call them mine; and which, when I talk
of a perception, feeling or thought as being _another persons_, I mean
to say that it has _not_ got to any of mine. I can, therefore, merely
from observation of _this_ class of data never obtain the slightest
reason for belief in the existence of a feeling, perception, or thought
which does _not_ stand in these relations to one of mine--which _is,_
that is to say, the feeling, perception or thought, of another person.
But how different is the case, if we adopt the hypothesis, which I wish
to recommend--if we assume the existence of that other class of data
which I have called "sense-contents!" On this hypothesis, that which I
perceive, when I perceive a movement of my own body, is _real_; that
which I perceive when I perceive a movement of another's body is _real_
also. I can now observe not merely the relation between my _perception_
of a movement of my body and my own feelings, but also a relation
between a _real_ movement of my body and my own feelings. And there
is no reason why I should not be justified in inferring that another
person's feelings stand _in the same relation_ to the real movements of
his body, in which I observe my own feelings to stand to similar real
movements of mine.
But there is another argument which may still be urged by those who
hold that my own perceptions, thoughts, and feelings, by themselves,
may be sufficient to justify a belief in the existence of other
persons. It may be said: "Our observation of our own perceptions may be
sufficient to _verify_ or _confirm_ the hypothesis that other persons
exist. This hypothesis is one which "works." The assumption that other
persons have particular thoughts, feelings and perceptions enables us
to predict that they will have others and that our own perceptions will
be modified accordingly: it enables us to predict future perceptions of
our own; and we find that these predictions are constantly verified.
We observe that we do have the perceptions, which the hypothesis leads
us to expect we should have. In short, our perceptions occur just as
they would do, _if_ the hypothesis were true; our perceptions behave
_as if_ other persons had the perceptions, thoughts and feelings which
we suppose them to have. Surely, then, they confirm the truth of the
hypothesis--they give some reason to think it probably true?"
All this, which I have supposed an opponent to urge, I admit to be
true. I admit that the fact that an hypothesis works may give some
reason to suppose it true. I admit that my perceptions occur just as
they would do, if other people had the perceptions which I suppose them
to have. I admit that that assumption enables me to make predictions as
to future perceptions of my own, and that I observe these predictions
to come true. I admit all this. But I admit it only in a sense in
which it in no way conflicts with the position which I am maintaining.
The words, which I have put into the mouth of a supposed opponent,
may, in fact, mean three different things, which it is worth while to
distinguish. In two of those meanings, which I shall admit to be true
and which are what make them seem plausible, they do not deny what I
assert. Only in the third sense are they an objection to my position:
and in that sense they are false.
One of the meanings which I admit to be true is as follows:--I have not
only admitted but insisted that some of my perceptions are just such
as would occur if another person had certain particular feelings: I
have insisted that I should not have just those perceptions which I do
have, unless some other person had certain feelings and perceptions
which I suppose him to have. And I admit further that the fact that I
have one of the perceptions in question--for instance, that of another
person's hand catching hold of his foot--this fact, _together with_
the true assumption that I should not have this perception, unless
some other person felt pain, will justify the assertion that another
person has felt pain. In this sense, I admit, the fact that I perceive
what I do perceive will give me reason to suppose that another person
has felt pain. And, on the other hand, I also admit that the fact
that I have this perception, _together with_ the true assumption that
when I have it another person has felt pain, may help to justify the
assumption that the perception in question is one which I should not
have had unless another person had felt pain--it helps to justify the
generalisation that certain of my perceptions are just what would
occur, _if_ another person had felt pain. In general terms, that is to
say, I admit that the occurrence of B, _together with_ the assumption
that B is just the sort of thing which would occur if A existed, will
justify the assertion that A exists in that particular instance. And
I also admit that the occurrence of B, _together with_ the assumption
that A exists in that particular instance, may help to justify the
assumption that B is just the sort of thing which would exist, if A
existed. In other words: When it is said that the observation of B's
existence confirms or verifies the assumption that A exists, either of
two things may be meant. It may be meant that, assuming B to be the
sort of thing which would exist if A existed, the observation of B
confirms the assumption that A exists _in this particular instance._
Or, on the other hand, it may be meant that, assuming A to exist
in this particular instance, the observation of B may confirm the
generalisation, that B is just the sort of thing which would exist,
if A existed. _Either_ the one _or_ the other of these two things is,
I think, what is generally assumed, when it is assumed that what we
do observe confirms or verifies the assumption that there exists some
particular thing which we don't observe. And I am admitting that both
these assumptions are true.
But neither of them conflicts in any way with the position I am
maintaining. What I am maintaining is that no observation of my own
perceptions, _by itself,_ can confirm the generalisation that any one
of them _is_ just what would occur if another person had a particular
feeling. I admit this generalisation to be true; and I admit that my
observation of my own perceptions and feelings may give me _reason_ to
suppose that _if_ another person has certain perceptions or feelings
_he_ will also have certain others. What I deny is that they give
me the slightest reason to suppose that the existence of any such
feeling or perception in another has any connection with the existence
of any perception _of my own_--to suppose that any perception of my
own is the sort of thing which would occur _if_ another person had a
particular feeling. What therefore, my opponent must affirm is that the
observation of a perception of my own _without_ the assumption (which
Reid makes) that in that particular instance any feeling or perception
of another person, of any kind whatever, has preceded it, may give me
reason to suppose that that perception of my own is of a kind which is
generally preceded by a particular kind of feeling in another person.
And this, I think, is plainly false.
But there is yet a third thing which may be meant, and which I
am willing to admit may be true. It may be said: "I believe many
generalisations of the following kind. I believe that when I have
a perception A, some other person has generally had a feeling X; I
believe that the existence of the feeling X is generally followed, in
the same person, by that of the feeling Y; and I believe also that
when another person has the feeling Y, I generally have the perception
B. I believe all this." And it must, I think, be admitted that we do
believe generalisations of this kind, and generalisations in which
there are not merely two steps between A and B, but a great number of
steps. "But then," it may be said, "my belief in this generalisation
causes me, when I observe my perception A, to expect that I shall have
the perception B; and such expectations, I observe, are constantly
realised." And this also, I think, must be admitted to be true. "But,
finally," it may be said, "beliefs which produce expectations which
are constantly realised are generally true. And hence the fact that
these beliefs of mine about the connection of feelings in other persons
with perceptions of my own do lead to expectations which are realised,
gives me reason to suppose that these generalisations are true and
hence that other persons do have particular kinds of feelings."
And I am willing to admit that this also is true. I am willing to
admit that true predictions can, as a rule, only be produced by true
beliefs. The generalisation that this is so, is, indeed, one which
can only be justified by the observations of beliefs, which are, in
some way, independently proved to be true; and hence, if it is to be
justified, without assuming the existence of anything other than my
own perceptions, thoughts, and feelings, it can only be justified by
my observation that beliefs with regard to the manner in which _these_
succeed one another generally lead to true predictions. Whether the
observation of such beliefs _alone_ could give sufficient reason for
it, is, I think, doubtful; but I am willing to admit that it may be
so. One thing, however, is, I think, quite plain: namely, that this
generalisation "Beliefs which lead to true predictions are generally
true" cannot be true, _unless_ some other of the "contents" which I
observe, beside my own perceptions, thoughts, and feelings, do exist.
That is to say, in giving a reason for supposing the existence of
other people, this generalisation also gives a reason for the very
theory which I am advocating, namely, that some of those data which
I have called "sense-contents" do exist. It does this, because it is
quite certain that beliefs in generalisations about the existence of
sense-contents _can_ (and do) constantly lead to true predictions. The
belief that when I have observed a fire of a certain size in my grate,
something similar to what I have observed will continue to exist for
a certain time, can, and constantly does, lead to the true prediction
that, when I come back to my room in half an hour's time, I shall
observe a fire of a certain size still burning. We make predictions
on such grounds, I think, every day and all day long. And hence
unless such beliefs as that what I observe when I see a fire burning
_does_ exist, _are_ true, we certainly have no reason to suppose that
beliefs which lead to true predictions are generally true. And hence
on this hypothesis also it remains true: that, unless some of the
contents which I observe _other_ than my own perceptions, thoughts, and
feelings, do exist, I cannot have the slightest reason for supposing
that the existence of certain perceptions of my own is generally
connected with that of certain perceptions, thoughts, or feelings in
any other person.
I conclude therefore that, unless some of the observed data which I
have called sense-contents _do_ exist, my own observations cannot give
me the slightest reason for believing that anybody else has ever had
any particular perception, thought, or feeling. And, having arrived
so far towards an answer to my first question: How do we know that
any other persons exist? I may now point out that precisely the same
answer must be given to my second question: How do we know that _any_
particular kind of thing exists, other than ourselves, our perceptions,
thoughts, and feelings, and what we directly perceive? There is a view
concerning what exists, which deserves, I think, much more respect than
it generally receives from philosophers nowadays. The view I mean is
the view that material objects, such as they are conceived by physical
science, do really exist. It is held by some persons (and Reid is among
them) that we _do_ know of the existence, not only of other persons,
but also of the movements of matter in space. It is held that we do
know, with considerable precision, what kinds of movements of matter
generally precede my perception, when I have a particular perception.
It is held, for instance, that when I perceive a red and blue book side
by side on a shelf, at a certain distance from me, there have existed,
between two material objects, which may be called books, and another
kind of material object, which may be called my eyes, certain wave-like
motions of a material medium; that there have existed two different
sets of waves, of which the one is connected with my perception of red
and the other with my perception of blue; and that the relative heights
and breadths of the two different sets of waves, and the relative
velocity of their movements are very exactly known. It is held that
some men have a vast amount of very precise information about the
existence of objects of this kind; and I think the view that this is
so deserves a great deal of respect. But what I wish now to point out
is that no one's observation of his own perceptions, thoughts and
feelings, can, by itself, give him the slightest reason for believing
in the existence of any such material objects. All the arguments by
which I have tried to show that this kind of observation alone can give
me no reason to believe in the existence of any kind of perception
or feeling in another person, apply, with at least equal force, to
show that it can give me no reason to believe in the existence of any
kind of material object. On the other hand, if we are to admit the
principle that "Beliefs which lead to true predictions, are generally
true," this principle will give us at least as much reason to believe
in the existence of certain kinds of material objects as to believe
in the existence of other persons; since one of the most remarkable
facts about beliefs in the existence of such objects is that they do so
often lead to true predictions. But it must be remembered that we can
have no reason for believing this principle itself, _unless_ our own
perceptions, thoughts and feelings are _not_ the only kind of observed
"content" which really does exist: we can have no reason for it, unless
some such things as what I perceive, when I see a red and blue book
side by side, do really exist.
It would seem, therefore, that if my own observations do give me any
reason whatever for believing in the existence either of any perception
in any other person or of any material object, it must be true that
not only my own perceptions, thoughts and feelings, but also _some_ of
the other kinds of things which I directly perceive--colours, sounds,
smells, etc.--do really exist: it must be true that some objects of
this kind _exist_ or are _real_ in precisely the same simple sense
in which my perceptions of them exist or are real. Is there then any
reason to think that this is not true? Is there any reason to think,
for instance, that _none_ of the colours which I perceive as occupying
areas of certain shapes and sizes really exist in the areas which
they appear to occupy? This is a question which I wished to discuss
at length, because I think that it is one in which there are real
difficulties. But I have given so much space to other questions, that I
can only deal with it very briefly here.
Some philosophers are very fond of asserting that a colour cannot exist
except when it is perceived; and it might possibly be thought that
when I suggest that colours do really exist, I am suggesting that they
do exist when they are not perceived. I wish, therefore, briefly to
point out that the question whether anything does exist, when it is
not perceived, is one which I have not argued and shall not attempt
to argue in this paper. I have, indeed, tried to show that since
"exists" does not _mean_ "is perceived," it is, at least, conceivable
that things should exist, when they are not perceived. But I have
admitted that it is quite possible none _do_ so: it _may_ be the case
that whenever a thing exists, it is _also_ at the same time perceived,
for anything that I have said or shall say to the contrary. I think,
indeed, that, if such things as colours _do_ exist, my observation of
their behaviour will justify me in concluding that they also exist when
I myself am, at least, not aware of perceiving them: but since I have
not attempted to determine what kinds of observation are sufficient to
justify a generalisation, I do not pretend to say whether this is so
or not: and still less do I pretend to say whether, _if_ they exist
when _I_ do not perceive them, we are justified in supposing that
someone else must be perceiving them. The question whether anything
exists, when it is not perceived, and, if so, what things, seems to
me to be one which can only be settled by observation; and thus, I
conceive, observation might justify us in concluding that certain kinds
of things--pains, for example, do _not_ exist, when they are not
perceived and that other kinds of things--colours, for example, _do_
exist, when they are not perceived. The only way, in which, so far as
I am aware, the theory I am advocating does conflict with ordinary
Idealistic conclusions, is that it does suggest that things, which are
_not_ "spiritual," do _sometimes_ exist, as really and as truly, as
things which are.
The theory, therefore, that nothing exists, except when it is
perceived, is no objection (even if it be true) to the supposition that
colours do exist. What objections are there to this supposition? All
serious objections to it are, I think, of one type. They all rest upon
the assumption that, if a certain kind of thing exists at a certain
time in a certain place, certain other kinds of things cannot exist at
the same time in the same place. They are all, that is to say, of the
same type as Berkeley's argument: that, though the same body of water
may _appear_ to be simultaneously both hot and cold (if one of the
hands we plunge into it is warm and the other cold), yet the heat and
the cold cannot both _really_ be in the same body at the same time. And
it is worth noticing that anyone who uses this argument must admit that
he understands what is meant by "really existing in a given place," and
that he means by it something _other_ than "being perceived as in a
given place." For the argument itself admits that _both_ the heat _and_
the cold _are_ really _perceived_ as being in the same place, and that
there is no difficulty in supposing that they are so; whereas It urges
that there _is_ a difficulty in supposing that they both _really exist_
in it.
Now there is one obvious defect in this type of argument, if designed
to prove that _no_ sensible quality exists at any place where it
is perceived as being--a defect, which Berkeley himself admits in
his "Principles," though he omits to notice it where he repeats the
argument in his "Hylas." Even if we assume that the heat and the
cold cannot _both_ exist in the same place (and I admit that, in this
case, the contrary assumption does seem repugnant to Common Sense),
it does not follow that _neither_ exists there. That is to say this
type of argument, even if we grant its initial assumption, will only
entitle us to conclude that _some_ sensible qualities which we perceive
as being in a certain place at a certain time, do not exist in that
place at that time. And this conclusion, I am inclined to think, is
true. In the case, for instance, of the so-called "images" which
we perceive in a looking-glass, we may very readily admit that the
colours and shapes which we perceive do _not_ exist at the places where
they appear to be--namely at various distances behind the glass. But
yet, so far as I can see, we have no reason whatever for supposing
that they do not, _except_ the assumption that our observations give
us reason to believe that _other_ sensible qualities _do_ exist in
those positions behind the glass; and the assumption that _where_
these _other_ sensible qualities do exist, those which we see in the
glass do _not_ exist. I should, therefore, admit that _some_ sensible
qualities which we perceive as being in certain places, do _not_ exist
in those places, while still retaining my belief that others do. And
_perhaps_ this explanation is the one which should also be adopted in
the case of sensible qualities which appear to be at a great distance
from us. When, for instance, (as we say), "we see the moon," _what_
we perceive (if the moon be full) is a round bright silver disc, of
a small size, at a place very distant from us. Does that silver disc
exist at that place? With what suppositions does the assumption that
it _does_ conflict? Only, so far as I can see, with the supposition
that the place in question is _really_ occupied by a body such as
science has taught us to suppose that the moon _really_ is--a spherical
body immensely larger than objects, in comparison with which the
silver disc which we perceive is small; _or else_ with the supposition
that the place in question is really occupied by some part of our
atmosphere, or some part of the medium which science supposes to exist
between our atmosphere and the moon; _or else_ with the supposition
that the place in question is really occupied by what we might see,
if the moon were nearer to us by many thousands of miles. Unless we
suppose that some other object _is_ in the place, in which the silver
disc appears to be, and that this object is of a kind which cannot
occupy the _same_ place which is occupied by a silver disc, we have
no reason to suppose that the silver disc does _not_ really exist in
the place where it appears to be. And, in this case, we _perhaps_ have
reason for both suppositions and should therefore conclude that the
silver disc, which we perceive, does not exist in any real place.
Part, therefore, of these objections to our theory may, I think, be
met by admitting that _some_ of the ... sensible qualities which we
perceive do not exist at the places where they appear to exist, though
ethers do. But there is, I think, another class of cases, in which we
may be justified in denying that two things which (it is asserted)
cannot occupy the same space, really cannot. I will take an instance
which is, I think, typical. When we look at a drop of blood with the
naked eye, we perceive a small red spot, uniformly red all over. But
when (as we say) we look at the _same_ object under a microscope of
a certain power, I am informed that we see a much larger spot, of
similar shape, indeed, but _not_ uniformly red--having, in fact, small
red spots at different positions in a yellowish field. And if we were
again to look at the _same_ object through a microscope of much higher
power still, we might perceive yet a third different arrangement of
colours. Is there any fatal objection to supposing that all _three_
appearances--the uniform red spot, the yellowish field with reddish
spots in it, and the third, whatever that may be--do all really occupy
the same real spatial area? I cannot see that there is. We are familiar
with the idea that a given spatial area may contain parts which are
invisible to us. And hence, I think it is quite conceivable that parts
of a given area may be _really_ occupied by one colour, while the whole
is _really_ occupied by another. And this, I think, is what we actually
_do_ believe in many cases. At all events, we certainly believe that
the area which appears to be occupied by one colour really is _the same
area_ as that which appears to be occupied by another. And, unless
we assume that the area, in both cases, really is the same, we can
certainly have no reason to deny that each colour does really occupy
the area which it appears to occupy.
For these reasons I think that the difficulties in the way of supposing
that _some_ of the sensible qualities which we perceive as being in
certain places, really exist in the places in which we perceive them
to be, are not insuperable. I have indeed not done justice to these
difficulties; but then, neither have I done justice to what is to be
said on the other side. At all events, I think it is plain that we have
no reason to assert, in any case whatever, that a perceived colour
does _not_ really exist in the place where it is perceived as being,
_unless_ we assume that that very same place really is occupied by
something else_--either_ by some different sensible qualities _or_ by
material objects such as physical science supposes to exist. But what
reason can we give for such an assumption? I have tried to show that
our own observations can give us none, _unless_ we assume that some of
the sensible qualities, which we observe as occupying certain places,
do really exist in those places. And, if this is so, then we must
admit that neither he who believes (with Reid) in the existence of
other minds and of matter also, nor he who believes in the existence
of other minds and denies that of matter, can have, in his own
observations, the slightest reason either for his assertion or for his
denial: we must admit that he can have no reason for either assertion
or denial, except one which consists in the assumption of the existence
or nonexistence of something which he does _not_ observe--something,
therefore, of the very same kind as that for which he gives it as a
reason. I am very unwilling to suppose that this is the case: I am
very unwilling to suppose that he who believes that Sindbad the Sailor
really saw what the "Arabian Nights" represent him as seeing, has just
as good reason (so far as his own observation goes) for believing this
as he who denies it has for denying it. Still this may be the case.
We _must_, perhaps, be content to assume as certain that for which
our observation gives no reason: to assume such propositions as that
Sindbad did _not_ see a Roc, and that you _do_ hear my voice. But if it
is said that these things are certain; then it also appears to me to
be certain that the colours which I perceive do exist (_some_ of them)
where I perceive them. The more I look at objects round me, the more I
am unable to resist the conviction that what I see does exist, as truly
and as really, as my perception of it The conviction is overwhelming.
This being, then, the state of the case, I think I may at least plead
that we have grounds for suspense of judgment as to whether what I
see does _not_ really exist; grounds, too, for renewed enquiry, more
careful than such enquiry has sometimes been in the past.
[1] Not now in 1921.