There are two beliefs in which almost all philosophers, and almost all
ordinary people are agreed. Almost everyone believes that he himself
and what he directly perceives do not constitute the whole of reality:
he believes that _something_ other than himself and what he directly
perceives _exists_ or is _real._ I do not mean to say that almost
everyone believes that what he directly perceives is real: I only mean
that he does believe that, whether what he directly perceives is real
or not, something other than it and other than himself certainly is so.
And not only does each of us thus agree in believing that _something_
other than himself and what he directly perceives is real: almost
everyone also believes that _among_ the real things, other than himself
and what he directly perceives, are other persons who have thoughts
and perceptions in some respects similar to his own. That most people
believe this I think I need scarcely try to show. But since a good many
philosophers may appear to have held views contradictory of this one, I
will briefly point out my reason for asserting that most philosophers,
even among those (if any) who have believed the contradictory of this,
have yet held this as well. Almost all philosophers tell us something
about the nature of _human_ knowledge and _human_ perception. They tell
us that _we_ perceive so and so; that the nature or origin of _our_
perceptions is such and such; or (as I have just been telling you) that
men in general have such and such beliefs. It might, indeed, be said
that we are not to interpret such language too strictly: that, though
a philosopher talks about _human_ knowledge and _our_ perceptions,
he only means to talk about his own. But in many cases a philosopher
will leave no doubt upon this point, by expressly assuming that there
are other perceptions, which differ in some respects from his own:
such, for instance, is the case when (as is so common nowadays) a
philosopher introduces psycho-genetic considerations into his arguments
--considerations concerning the nature of the perceptions of men who
existed before and at a much lower stage of culture than himself.
Any philosopher, who uses such arguments, obviously assumes that
perceptions other than his own have existed or been real. And even
those philosophers who think themselves justified in the conclusion
that neither their own perceptions nor any perceptions like theirs are
_ultimately_ real, would, I think admit, that _phenomenally_, at least,
they _are_ real, and are certainly _more_ real than some other things.
Almost everyone, then, does believe that some perceptions other than
his own, and which he himself does not directly perceive, are real; and
believing this, he believes that something other than himself and what
he directly perceives is real. But how do we know that anything exists
except our own perceptions, and what we directly perceive? How do we
know that there are any other people, who have perceptions in some
respects similar to our own?
I believe that these two questions express very exactly the nature of
the problem which it is my chief object, in this paper, to discuss.
When I say these words to you, they will at once suggest to your minds
the very question, to which I desire to find an answer; they will
convey to you the very same meaning which I have before my mind, when I
use the words. You will understand at once what question it is that I
mean to ask. But, for all that, the words which I have used are highly
ambiguous. If you begin to ask yourselves what I do mean by them, you
will find that there are several quite different things which I might
mean. And there is, I think, great danger of confusing these different
meanings with one another. I think that philosophers, when they have
asked this question in one sense, have often answered it in quite a
different sense; and yet have supposed that the answer which they have
given is an answer to the very same question which they originally
asked. It is precisely because there is this ambiguity--this danger of
confusion, in the words which I have used, that I have chosen to use
them. I wish to point out as clearly as I can, not only what I do mean
by them, but also some things which I do _not_ mean; and I wish to make
it clear that the questions which I do _not_ mean to ask, are different
questions from that which I do mean to ask.
I will take the second of my two questions, since there is in the other
an additional ambiguity to which I do not now wish to call attention.
My second question was: How do we know that there exist any other
people who have perceptions in some respects similar to our own? What
does this question mean?
Now I think you may have noticed that when you make a statement to
another person, and he answers "How do you know that that is so?" he
very often means to suggest that you do _not_ know it. And yet, though
he means to suggest that you do not _know_ it, he may not for a moment
wish to suggest that you do not _believe_ it, nor even that you have
not that degree or kind of conviction, which goes beyond mere belief,
and which may be taken to be essential to anything which can properly
be called knowledge. He does not mean to suggest for a moment that you
are saying something which you do not believe to be true, or even that
you are not thoroughly convinced of its truth. What he does mean to
suggest is that what you asserted was not _true_, even though you may
not only have believed it but felt sure that it was true. He suggests
that you don't _know_ it, in the sense that what you believe or feel
sure of is not true.
Now I point this out, not because I myself mean to suggest that we
don't know the existence of other persons, but merely in order to show
that the word "know" is sometimes used in a sense in which it is not
merely equivalent to "believe" or "feel sure of." When the question
"How do you _know_ that?" is asked, the questioner does not merely
mean to ask "how do you come to believe that, or to be convinced of
it?" He sometimes, and I think generally, means to ask a question with
regard to the _truth_, and not with regard to the _existence_ of your
belief. And similarly when I ask the question "How do we know that
other people exist?" I do _not_ mean to ask "How do we come to believe
in or be convinced of their existence?" I do not intend to discuss this
question _at all._ I shall not ask what _suggests_ to us our belief in
the existence of other persons or of an external world; I shall not
ask whether we arrive at it by inference or by "instinct" or in any
other manner, which ever has been or may be suggested: I shall discuss
no question of any kind whatever with regard to its origin, or cause,
or the way in which it arises. These psychological questions are _not_
what I propose to discuss. When I ask the question "How do we know that
other people exist?" I do _not_ mean:
"How does our belief in their existence arise?"
But if I do not mean this what do I mean P I have said that I mean
to ask a question with regard to the _truth_ of that belief; and the
particular question which I mean to ask might be expressed in the
words: _What reason have_ we for our belief in the existence of other
persons? But these are words which themselves need some explanation,
and I will try to give it.
In the first place, then, when I talk of "a reason," I mean _only_
a good reason and _not_ a bad one. A bad reason is, no doubt, a
reason, in one sense of the word; but I mean to use the word "reason"
exclusively in the sense in which it is equivalent to "good reason."
But what, then, is meant by a good reason for a belief? I think I can
express sufficiently accurately what I mean by it in this connection,
as follows:--A good reason for a belief is a proposition which is
true, and which would not be true unless the belief were also true. We
should, I think, commonly say that when a man knows such a proposition,
he has a good reason for his belief; and, when he knows no such
proposition, we should say that he has no reason for it. When he knows
such a proposition, we should say he knows something which is a reason
for thinking his belief to be true--something from which it _could_ be
validly inferred. And if, in answer to the question "How do you know
so and so?" he were to state such a proposition, we should, I think,
feel that he had answered the question which we meant to ask. Suppose,
for instance, in answer to the question "How do you know that?" he were
to say "I saw it in the _Times."_ Then, if we believed that he had
seen it in the _Times_, and also believed that it would not have been
in the _Times_, unless it had been true, we should admit that he had
answered our question. We should no longer doubt that he did _know_
what he asserted, we should no longer doubt that his belief was true.
But if, on the other hand, we believed that he had not seen it in the
_Times_--if, for instance, we had reason to believe that what he saw
was not the statement which he made, but some other statement which
he mistook for it; or if we believed that the kind of statement in
question was one with regard to which there was no presumption that,
being in the _Times_, it would be true: in _either_ of these cases
we should, I think, feel that he had _not_ answered our question. We
should still doubt whether what he had said was true. We should still
doubt whether he _knew_ what he asserted; and since a man cannot tell
you how he _knows_ a thing unless he does know that thing, we should
think that, though he might have told us truly how he _came to believe
it,_ he had certainly not told us how he _knew_ it. But though we
should thus hold that he had _not_ told us _how he knew_ what he had
asserted, and that he had given us no reason for believing it to be
true; we must yet admit that he had given us a reason in a sense--a
_bad_ reason, a reason which was no reason because it had no tendency
to show that what he believed was true; and we might also be perfectly
convinced that he had given us _the reason_ why he believed it--the
proposition by believing which he was induced also to believe his
original assertion.
I mean, then, by my question, "How do we know that other people
exist?" what, I believe, is ordinarily meant, namely, "What reason
have we for believing that they exist?" and by this again I mean, what
I also believe is ordinarily meant, namely, "What proposition do we
believe, which is both true itself and is also such that it would not
be true, unless other people existed?" And I hope it is plain that
this question, thus explained, is quite a different question from the
psychological question, which I said I did _not_ mean to ask--from the
question, "How does our belief in the existence of other people arise?"
My illustration, I hope, has made this plain. For I have pointed out
that we may quite well hold that a man has told us how a belief of
his arises, and even what was the reason which made him adopt that
belief, and yet may have failed to give us any _good reason_ for his
belief--any proposition which is both true itself, and also such that
the truth of his belief follows from it. And, indeed, it is plain that
if any one ever believes what is false, he is believing something for
which there _is_ no good reason, in the sense which I have explained,
and for which, therefore, he cannot possibly have a good reason; and
yet it plainly does not follow that his belief did not arise in anyway
whatever, nor even that he had no reason for it--no bad reason. It
is plain that false beliefs do arise in some way or other--they have
origins and causes: and many people who hold them _have_ bad reasons
for holding them--their belief does arise (by inference or otherwise)
from their belief in some other proposition, which is not itself true,
or else is not a _good_ reason for holding that, which they infer
from it, or which, in some other way, it induces them to believe. I
submit, therefore, that the question, "What good reason have we for
believing in the existence of other people?" is different from the
question, "How does that belief arise?" But when I say this, I must
not be misunderstood; I must not be understood to affirm that the
answer to both questions _may_ not, in a sense, be the same. I fully
admit that the very same fact, which suggests to us the belief in the
existence of other people, _may_ also be a good reason for believing
that they do exist. All that I maintain is that the question whether
it is a good reason for that belief is a different question from the
question whether it suggests that belief: if we assert that a certain
fact _both_ suggests our belief in the existence of other persons and
is _also_ a good reason for holding that belief, we are asserting two
different things and not one only. And hence, when I assert, as I shall
assert, that we _have_ a good reason for our belief in the existence
of other persons, I must not be understood also to assert either that
we infer the existence of other persons from this good reason, or that
our belief in that good reason suggests our belief in the existence
of other persons in any other way. It is plain, I think, that a man
may believe two true propositions, of which the one would not be true,
unless the other were true too, without, in any sense whatever, having
arrived at his belief in the one _from_ his belief in the other; and it
is plain, at all events, that the question whether his belief in the
one _did_ arise from his belief in the other, is a different question
from the question whether the truth of the one belief follows from the
truth of the other.
I hope, then, that I have made it a little clearer what I mean by the
question: "What reason have we for believing in the existence of other
people?" and that what I mean by it is at all events different from
what is meant by the question: "How does our belief in the existence of
other people arise?"
But I am sorry to say that I have not yet reached the end of my
explanations as to what my meaning is. I am afraid that the subject may
seem very tedious. I can assure you that I have found it excessively
tedious to try to make my meaning clear to myself. I have constantly
found that I was confusing one question with another, and that, where
I had thought I had a good reason for some assertion, I had in reality
no good reason. But I may perhaps remind you that this question, "How
do we know so and so?" "What reason have we for believing it?" is one
of which philosophy is full; and one to which the most various answers
have been given. Philosophy largely consists in giving reasons; and the
question what are good reasons for a particular conclusion and what are
bad, is one upon which philosophers have disagreed as much as on any
other question. For one and the same conclusion different philosophers
have given not only different, but incompatible, reasons; and
conversely different philosophers have maintained that one and the same
fact is a reason for incompatible conclusions. We are apt, I think,
sometimes to pay too little attention to this fact. When we have taken,
perhaps, no little pains to assure ourselves that our own reasoning
is correct, and especially when we know that a great many other
philosophers agree with us, we are apt to assume that the arguments
of those philosophers, who have come to a contradictory conclusion,
are scarcely worthy of serious consideration. And yet, I think, there
is scarcely a single reasoned conclusion in philosophy, as to which
we shall not find that some other philosopher, who has, so far as we
know, bestowed equal pains on his reasoning, and with equal ability,
has reached a conclusion incompatible with ours. We may be satisfied
that we are right, and we may, in fact, be so; but it is certain that
_both_ cannot be right: either our opponent or we must have mistaken
bad reasons for good. And this being so, however satisfied we may be
that it is not we who have done so, I think we should at least draw the
conclusion that it is by no means easy to avoid mistaking bad reasons
for good; and that no process, however laborious, which is in the least
likely to help us in avoiding this should be evaded. But it is at least
possible that one source of error lies in mistaking one kind of reason
for another--in supposing that, because there is, in one sense, a
reason for a given conclusion, there is also a reason in another, or
that because there is, in one sense, no reason for a given conclusion,
there is, therefore, no reason at all. I believe myself that this _is_
a very frequent source of error: but it is at least a possible one.
And where, as disagreements show, there certainly is error on one
side or the other, and reason, too, to suppose that the error is not
easy to detect, I think we should spare no pains in investigating any
source, from which it is even possible that the error may arise. For
these reasons I think I am perhaps doing right in trying to explain as
clearly as possible not only what reasons we have for believing in an
external world, but also in what sense I take them to be reasons.
I proceed, then with my explanation. And there is one thing, which, I
think my illustration has shown that I do _not_ mean. I have defined
a reason for a belief as a true proposition, which would not be true
unless the belief itself--what is believed--were also true; and I
have used, as synonymous with this form of words, the expressions: A
reason for a belief is a true proposition from which the truth of the
belief _follows_ from which it _could_ be _validly inferred._ Now these
expressions might suggest the idea that I mean to restrict the word
"reason," to what, in the strictest sense, might be called a _logical_
reason--to propositions from which the belief in question _follows,_
according to the rules of inference accepted by Formal Logic. But I
am _not_ using the words "follow," "validly inferred," in this narrow
sense; I do _not_ mean to restrict the words "reason for a belief"
to propositions from which the laws of Formal Logic state that the
belief could be deduced. The illustration which I gave is inconsistent
with this restricted meaning. I said that the fact that a statement
appeared in the _Times_ might be a good reason for believing that
that statement was true. And I am using the word "reason" in the wide
and popular sense, in which it really might be. If, for instance,
the _Times_ stated that the King was dead, we should think that was
a good reason for believing that the King was dead; we should think
that the _Times_ would not have made such a statement as that unless
the King really were dead. We should, indeed, not think that the
statement in the _Times_ rendered it absolutely _certain_ that the
King was dead. But it _is_ extremely unlikely that the _Times_ would
make a statement of this kind unless it were true; and, in that sense,
the fact of the statement appearing in the _Times_ would render it
_highly probable_--much more likely than not--that the King was dead.
And I wish it to be understood that I am using the words "reason for
a belief" in this extremely wide sense. When I look for a good reason
for our belief in the existence of other people, I shall not reject any
proposition merely on the ground that it only renders their existence
probable--only shows it to be more likely than not that they exist.
Provided that the proposition in question does render it _positively
probable_ that they exist, then, if it also conforms to the conditions
which I am about to mention, I shall call it a "good reason."
But it is not every proposition which renders it probable that
other people exist, which I shall consider to be a good answer to
my question. I have just explained that my meaning is wide in one
direction--in admitting _some_ propositions which render a belief
merely probable; but I have now to explain that it is restricted in
two other directions. I do mean to exclude certain propositions which
do render that belief probable. When I ask: What reason have _we_ for
believing in the existence of other people? a certain ambiguity is
introduced by the use of the plural "we." If each of several different
persons has a reason for believing that he himself exists, then it is
not merely probable, but certain, according to the rules of Formal
Logic, that, in a sense, _they_ "have a reason for believing" that
several people exist; each has a reason for believing that he himself
exists; and, therefore, all of them, taken together, have reasons for
supposing that several persons exist. If, therefore, I were asking
the question: What reason have _we_ for believing in the existence
of other persons? in this sense, it would follow that if each of us
has a reason for believing in his own existence, these reasons, taken
together, would be a reason for believing in the existence of all of
us. But I am not asking the question in this sense: it is plain that
this is not its natural sense. What I do mean to ask is: Does _each
single one_ of us know any proposition, which is a reason for believing
that _others_ exist? I am using "we," that is to say, in the sense
of "each of us." But again I do mean _each_ of us: I am not merely
asking whether some _one_ man knows a proposition which is a reason
for believing that other men exist. It would be possible that some
one man, or some few men, should know such a proposition, and yet the
rest know no such proposition. But I am not asking whether this is the
case. I am asking whether among propositions of the kind which (as we
commonly suppose) all or almost all men know, there is any which is a
reason for supposing that other men exist. And in asking this question
I am not begging the question by supposing that all men do exist. My
question might, I think, be put quite accurately as follows. There are
certain kinds of belief which, as we commonly suppose, all or almost
all men share. I describe this kind of belief as "our" beliefs, simply
as an easy way of pointing out which kind of belief I mean, but without
assuming that all men do share them. And I then ask: Supposing a
single man to have beliefs of this kind, which among them would be a
good reason for supposing that other men existed having like beliefs?
This, then, is the first restriction which I put upon the meaning
of my question. And it is, I think, a restriction which, in their
natural meaning, the words suggest. When we ask: What reason have
we for believing that other people exist? we naturally understand
that question to be equivalent to: What reason has _each_ of us for
that belief? And this question again is naturally equivalent to the
question: Which among the propositions that a single man believes, but
which are of the kind which (rightly or wrongly) we assume all men to
believe, are such that they would not be true unless some other person
than that man existed? But there is another restriction which, I think,
the words of my question also naturally suggest. If we were to ask
anyone the question: How do you know that you did see that statement
in the _Times_? and he were to answer "Because I did see it in the
_Times_ and in the _Standard_ too," we should not think that he had
given us a _reason_ for the belief that he saw it in the _Times._ We
should not think his answer a _reason_, because it asserts the very
thing for which we require a reason. And similarly when I ask: How
do we know that any thing or person exists, other than ourselves and
what we directly perceive? What reason have we for believing this? I
must naturally be understood to mean: What proposition, _other_ than
one which itself asserts or presupposes the existence of something
beyond ourselves and our own perceptions, is a reason for supposing
that such a thing exists? And this restriction obviously excludes an
immense number of propositions of a kind which all of us do believe. We
all of us believe an immense number of different propositions about
the existence of things which we do not directly perceive, and many
of these propositions are, in my sense, good reasons for believing in
the existence of still other things. The belief in the existence of a
statement in the _Times,_ when we have not seen that statement, may,
as I implied, be a good reason for believing that someone is dead. But
no such proposition can be a good answer to my question, because it
asserts the very kind of thing for which I require a reason: it asserts
the existence of something other than myself and what I directly
perceive. When I am asking: What reason have I for believing in the
existence of anything but myself, my own perceptions, and what I do
directly perceive? you would naturally understand me to mean: What
reason, _other than_ the existence of such a thing, have I for this
belief?
Each of us, then, we commonly assume, believes some true propositions,
which do not themselves assert the existence of anything other than
himself, his own perceptions, or what he directly perceives. Each of
us, for instance, believes that he himself has and has had certain
particular perceptions: and these propositions are propositions of
the kind I mean--propositions which do not themselves assert the
existence of anything _other than_ himself, his own perceptions,
and what he directly perceives: they are, I think, by no means the
only propositions of this kind, which most of us believe: but they
_are_ propositions of this kind. But, as I say, I am not assuming
that each of us--each of several different people--does believe
propositions of this kind. All that I assume is that at least one man
does believe some such propositions. And then I ask: Which among those
true propositions, which one man believes, are such that they would
probably not be true, unless some other man existed and had certain
particular perceptions? Which among them are such that it _follows_
(in the wide sense, which I have explained) from their truth, that it
is more likely than not that some other man has perceptions? This is
the meaning of my question, so far as I have hitherto explained it:
and I hope this meaning is quite clear. It is in this sense that I am
asking: What reason have we for believing that other people exist? How
do we know that they exist? This, indeed, is not _all_ that I mean by
that question: there is one other point--the most important one--which
remains to be explained. But this is _part_ of what I mean to ask; and
before I go on to explain what else I mean, I wish first to stop and
enquire what is the answer to this part of my question. What is the
answer to the question: Which among the true propositions, of a kind
which (as we commonly assume) each of us believes, and which do not
themselves assert the existence of anything other than that person
himself, his own perceptions, or what he directly perceives, are such
that they would probably not be true unless some other person existed,
who had perceptions in some respects similar to his own?
Now to this question the answer is very obvious. It is very obvious
that in this sense we have reasons for believing in the existence of
other persons, and also what some of those reasons are. But I wish
to make it quite plain that this is so: that in this sense one man
_has_ a reason for believing that another has certain perceptions. All
that I am asking you to grant, is, you see, that some of you would
not be having just those perceptions which you now have, unless I,
as I read this paper, were perceiving more or less black marks on a
more or less white ground; or that I on the other hand, should not
be having just those perceptions which I now have, unless some other
persons than myself were hearing the sounds of my voice. And I am
not asking you even to grant that this is certain--only that it is
positively probable--more likely than not. Surely it is very obvious
that this proposition is true. But I wish to make it quite clear
what would be the consequences of denying that any such propositions
are true--propositions which assert that the existence of certain
perceptions in one man are a reason for believing in the existence of
certain perceptions in another man--which assert that one man would
probably not have had just those perceptions which he did have, unless
some other man had had certain particular perceptions. It is plain, I
think, that, unless some such propositions are true, we have no more
reason for supposing that Alexander the Great ever saw an elephant,
than for supposing that Sindbad the Sailor saw a Roc; we have no more
reason for supposing that anybody saw Julius Caesar murdered in the
Senate House at Rome, than for supposing that somebody saw him carried
up to Heaven in a fiery chariot. It is plain, I think, that if we have
any reason at all for supposing that in all probability Alexander the
Great did see an elephant, and that in all probability no such person
as Sindbad the Sailor ever saw a Roc, part of that reason consists
in the assumption that some other person would probably not have had
just those perceptions which he did have, unless Alexander the Great
had seen an elephant, and unless Sindbad the Sailor had not seen a
Roc. And most philosophers, I think, are willing to admit that we have
some reason, in some sense or other, for such propositions as these.
They are willing to admit not only that some persons probably did see
Julius Caesar murdered in the Senate House; but also that some persons,
other than those who saw it, had and have _some reason_ for supposing
that some one else probably saw it. Some sceptical philosophers might,
indeed, deny both propositions; and to refute their views, I admit,
other arguments are needed than any which I shall bring forward in this
paper. But most philosophers will, I think, admit not only that facts,
for which there is, as we say, good historical evidence, are probably
true; but also that what we call good historical evidence really is
in some sense a good reason for thinking them true. Accordingly I am
going to assume that many propositions of the following kind are true.
Propositions, namely, which assert that one man would probably not
have certain perceptions which he does have, unless some other man had
certain particular perceptions. That some of you, for instance, would
probably not be having precisely the perceptions which you are having,
unless I were having the perception of more or less black marks on a
more or less white ground. And, in this sense, I say, we certainly have
reasons for supposing that other people have perceptions similar, in
some respects, to those which we sometimes have.
But when I said I was going to ask the question: What reason have we
for supposing that other people exist? you will certainly not have
thought that I merely meant to ask the question which I have just
answered. My words will have suggested to you something much more
important than merely this. When, for instance, I said that to the
question "How do you know that?" the answer "I saw it in the _Times"_
would be a satisfactory answer, you may have felt, as I felt, that it
would not in all circumstances be regarded as such. The person who
asked the question might, in some cases, fairly reply: "That is no
answer: how do you know that, because you saw a thing in the _Times_,
it is therefore true?" In other words he might ask fora _reason_ for
supposing that the occurrence of a particular statement in the _Times_
was a reason for supposing that statement true. And this is a question
to which we all believe that there may be an answer. We believe that,
with some kinds of statements which the _Times_ makes--some kinds of
statements with regard to Fiscal Policy for example--the fact that
the _Times_ makes them is no reason for supposing them to be true:
whereas with regard to other kinds of statements, which it makes, such
a statement, for instance, as that the King was dead, the fact that it
makes them _is_ a reason for supposing them true. We believe that there
are some kinds of statements, which it is very unlikely the _Times_
would make, unless they were true; and others which it is not at all
unlikely that the _Times_ might make, although they were not true. And
we believe that a reason might be given for distinguishing, in this
way, between the two different kinds of statement: for thinking that,
in some cases (on points, for instance, which, as we should say, are
not simple questions of fact) the _Times_ is fallible, whereas in other
cases, it is, though not absolutely infallible, very unlikely to state
what is not true.
Now it is precisely in this further sense that I wish to consider: what
reason have we for believing that certain particular things, other
than ourselves, our own perceptions, and what we directly perceive,
are real? I have asserted that I do have certain perceptions, which it
is very unlikely I should have, unless some other person had certain
particular perceptions; that, for instance, it is very unlikely I
should be having precisely those perceptions which I am now having
unless someone else were hearing the sound of my voice. And I now
wish to ask: What reason have I for supposing that this is unlikely?
What reason has any of us for supposing that any such proposition is
true? And I mean by "having a reason" precisely what I formerly meant.
I mean: What other proposition do I know, which would not be true,
unless my perception were connected with someone else's perception, in
the manner in which I asserted them to be connected? Here again I am
asking for _a good reason_; and am not asking a psychological question
with regard to origin. Here again I am not asking for a reason, in the
strict sense of Formal Logic; I am merely asking for a proposition
which would probably not be true, unless what I asserted were true.
Here again I am asking for some proposition of a kind which _each_ of
us believes; I am asking: What reason has _each_ of us for believing
that some of his perceptions are connected with particular perceptions
of other people in the manner I asserted?--for believing that he would
not have certain perceptions that he does have, unless some other
person had certain particular perceptions? And here again I am asking
for a _reason_--I am asking for some proposition _other_ than one
which itself asserts: When one man has a perception of such and such a
particular kind, it _is_ probable that another man has a perception or
thought of this or that other kind.
But what kind of reason can be given for believing a proposition of
this sort? For believing a proposition which asserts that, since one
particular thing exists, it is probable that another particular thing
also exists? One thing I think is plain, namely that we can have no
good reason for believing such a proposition, unless we have good
reason for believing some _generalisation._ It is commonly believed,
for instance, that certain so-called flint arrow-heads, which have been
discovered, were probably made by prehistoric men; and I think it is
plain that we have no reason for believing this unless we have reason
to suppose that objects which resemble these in certain particular
respects are _generally_ made by men--are _more often_ made by men
than by any other agency. Unless certain particular characteristics
which those arrow-heads have were characteristics which belonged at
least more frequently to articles of human manufacture than to any
articles not made by men, it would surely be just as likely as not
that these arrowheads were _not_ made by men--that they were, in fact
not arrow-heads. That is to say, unless we have reason to assert a
_generalisation_--the generalisation that objects of a certain kind
are _generally_ made by men, we have no reason to suppose that these
particular objects, which are of the kind in question, _were_ made
by men. And the same, so far as I can see, is true universally. If
we ever have any reason for asserting that, since one particular
thing exists, another probably exists or existed or will exist also
part of our reason, at least, must consist in reasons for asserting
some generalisation--for asserting that the existence of things of
a particular kind is, more often than not, accompanied or preceded
or followed by the existence of things of another particular kind.
It is, I think, sometimes assumed that an alternative to this theory
may be found in the theory that the existence of one kind of thing
"intrinsically points to," or is "intrinsically a sign or symbol of"
the existence of another thing. It is suggested that when a thing
which thus points to the existence of another thing exists, then it is
at least probable that the thing "pointed to" exists also. But this
theory, I think, offers no real alternative. For, in the first place,
when we say that the existence of one thing A is a "sign of" or "points
to" the existence of another thing B, we very commonly actually mean to
say that when a thing like A exists, a thing like B _generally_ exists
too. We may, no doubt, mean something else _too_; but this we do mean.
We say, for instance, that certain particular words, which we hear or
read, are a "sign" that somebody has thought of the particular things
which we call the meaning of those words. But we should certainly
hesitate to admit that the hearing or reading of certain words could be
called a "sign" of the existence of certain thoughts, unless it were
true that when those words are heard or read, the thoughts in question
_generally_ have existed. If when those words were heard or read, the
thoughts had generally _not_ existed, we should say that, in one sense
of the word at all events, the hearing of the words was _not_ a sign of
the existence of the thoughts. In this sense, therefore, to say that
the existence of A "points to" or "is a sign of" the existence of B is
actually to say that when A exists, B _generally_ exists also. But,
no doubt, the words "points to" "is a sign of" may be used in some
other sense: they may, for instance, mean only that the existence of A
_suggests_ in some way the belief that B exists. And in such a case we
certainly might know that the existence of A pointed to the existence
of B, without knowing that when A existed B generally existed also.
Let us suppose, then, that in some such sense A does "point to" the
existence of B; can this fact give us a reason for supposing it even
probable that B existed. Certainly it can, _provided_ it is true that
when A _does_ point to the existence of B, B _generally_ exists. But
surely it can do so, only on this condition. If when A _points_ to
the existence of B, B, nevertheless, does _not_ generally exist, then
surely the fact that A points to the existence of B can constitute no
probability that B does not exist: on the contrary it will then be
probable that, even though A "points to" the existence of B, B does
_not_ exist. We have, in fact, only substituted the generalisation that
A's _pointing to_ B is generally accompanied by the existence of B, for
the generalisation that A's _existence_ is generally accompanied by the
existence of B. If we are to have any reason for asserting that, when
A _points to_ or is a sign of the existence of B, B probably exists, we
must still have a reason for some generalisation--for a generalisation
which asserts that when one thing points to the existence of another,
that other _generally_ exists.
It is plain, then, I think, that if we are to find a reason for the
assertion that some particular perception of mine would probably not
exist, unless someone else were having or had had a perception of a
kind which I can name, we must find a reason for _some_ generalisation.
And it is also plain, I think, that in many cases of this kind the
generalisation must consist in an assertion that when one man has a
certain kind of perception, some other man generally has had some
other perception or belief. We assume, for instance, that when we hear
or read certain words, somebody besides ourselves has thought the
thoughts, which constitute the meaning of those words; and it is plain,
I think, that we have no reason for this assumption except one which
is also a reason for the assumption that when certain words are heard
or read, somebody generally has had certain thoughts. And my enquiry,
therefore, at least includes the enquiry: What reasons have we for such
generalisations as these? for generalisations which assert a connection
between the existence of a certain kind of perception in one man, and
that of a certain kind of perception or belief in another man?
And to this question, I think, but one answer can be given. If we
have any reason for such generalisations at all, some reason must
be given, in one way or another, by observation--by observation,
understood in the wide sense in which it includes "experiment." No
philosopher, I think, has ever failed to assume that observation does
give a reason for _some_ generalisations--for some propositions
which assert that when one kind of thing exists, another generally
exists or has existed in a certain relation to it. Even those who,
like Hume, imply that observation cannot give a _reason_ for anything,
yet constantly appeal to observation in support of generalisations of
their own. And even those who hold that observation can give no reason
for any generalisation about the relation of one man's perceptions to
another's, yet hold that it _can_ give a reason for generalisations
about the relation of some to others among a man's own perceptions.
It is, indeed, by no means agreed _how_ observation can give a reason
for any generalisation. Nobody knows what reason we have, if we have
any, for supposing that it can. But _that_ it can, everyone, I think,
assumes. I think, therefore, most philosophers will agree, that if we
can find any reason at all for generalisations of the kind in which
I am interested, a reason for _some_ of them at all events must be
found in observation. And what I propose to ask is: What reason can be
found in observation for even a single proposition of the kind I have
described? for a proposition which asserts that when one man has one
kind of perception, another man generally has or has had another.
But, when it is said that observation gives us a reason for
generalisations, two things may be meant neither of which I mean. In
the first place, we popularly use "observation" in a sense in which
we can be said to _observe_ the perceptions, feelings and thoughts
of other people: in which, therefore, we can be said to observe the
very things with regard to which I am asking what reason we have for
believing in their existence. But it is universally[1] agreed that
there is a sense in which no man can observe the perceptions, feelings
or thoughts of any other man. And it is to this strict sense that
I propose to confine the word. I shall use it in a sense, in which
we can certainly be said to observe nothing but ourselves, our own
perceptions, thoughts and feelings, and what we directly perceive. And
in the second place, it may be said that observations made by another
person may give _me_ a reason for believing some generalisation. And
it is certainly the case that for many of the generalisations in which
we all believe, if we have a reason in observation at all, it is not
in _our own_ observation that we have it: part of our reason, at all
events, lies in things which _other_ people have observed but which we
ourselves have not observed. But in asking this particular question,
I am not asking for reasons of this sort. The very question that I am
asking is: What reason has any one of us for supposing that any other
person whatever has ever made any observations? And just as, in the
first meaning which I gave to this question, it meant: What thing,
that any single man observes is such that it would probably not have
existed, unless some other man had made a particular observation?
So now I am asking: Which among the things, which _one single man
observes_, are such that they would probably not have existed, unless
it were true that some of them generally stood in certain relations to
observations of some other person? I am asking: Which among _my own_
observations give me a reason for supposing that some of them are of
a kind which are generally preceded or accompanied by observations
of other people? Which, for instance, among my own observations give
a good reason for the generalisation that when I hear certain words,
somebody else has generally had certain particular thoughts, or that
whenever anyone hears certain words, somebody else has generally had
the thoughts which constitute what we call the meaning of those words?
I am asking: Which among the vast series of observations, which any
one individual makes during his lifetime, give a good reason for
any generalisation _whatever_ of this kind--a generalisation which
asserts that some of them are generally preceded by certain thoughts,
perceptions or feelings in other persons? I quite admit that there
are some generalisations of this kind for which the observations of
_some_ particular men will _not_ give a reason. All that I ask is:
Is there even _one_ generalisation of this kind, for which the kind
of observations, which (as we commonly assume) each man, or nearly
every man does make, do give a reason? Among observations of the kind
which (as we commonly assume) are common to you and to me, do yours,
by themselves, give any reason for even _one_ such generalisation?
And do mine, by themselves, give any reason for even _one_ such
generalisation? And if they do, which, among these observations, is it
which do so?
My question is, then: What reason do my own observations give me, for
supposing that any perception whatever, which I have, would probably
not occur, unless some other person had a certain kind of perception?
What reason do my own observations give me for supposing, for instance,
that I should not be perceiving what I do now perceive, unless
someone were hearing the sound of my voice? What reason do your own
observations give you for supposing that you would not be perceiving
just what you are perceiving, unless I were perceiving more or less
black marks on a more or less white ground? The question does, I
think, appear to be a reasonable one; and most philosophers, I think,
have assumed that there is an answer to it. Yet it may be said that
there is no answer to it: that my own observations give me no reason
whatever for any single proposition of this kind. There are certain
philosophers (even apart from thorough sceptics, with whom, as I have
said, I am not now arguing) who have denied that they do. There are
certain philosophers who hold that nothing which any single one of
us observes or can observe, gives the slightest reason for supposing
that any of his own perceptions are generally connected with certain
perceptions in other people. There are philosophers who hold that the
only generalisations for which our own observations do give any warrant
are generalisations concerning the manner in which our own perceptions,
thoughts and feelings do and probably will succeed one another; and who
conclude that, this being so, we have no reason whatever for believing
in the existence of any other people. And these philosophers are, I
think, right in drawing this conclusion from this premiss. It does
not, indeed, follow from their premiss that we have not a reason in
the sense which I first explained, and in which, I insisted, it must
be admitted that we have a reason. It does not follow that some of our
perceptions _are_ not such as would probably not exist, unless some
other person had certain perceptions. But, as I have urged, when we
say that we have a reason for asserting the existence of something not
perceived, we commonly mean something more than this. We mean not only
that, since what we perceive does exist, the unperceived thing probably
exists too; we mean also that we have some reason for asserting this
connection between the perceived and the unperceived. And holding, as
we do, that no reason can be given for asserting such a connection,
except observation, we should say that, if observation gives no reason
for asserting it, we have _no_ reason for asserting it; and having no
reason for asserting this connection between the perceived and the
unperceived, we should say that we have none either for asserting the
even probable existence of the unperceived. This, I think, is what
we commonly mean by saying that we have no reason to believe in the
existence of a particular thing which we do not perceive. And hence,
I think, those philosophers who hold that our own observations give
us no reason whatever for any generalisation whatever concerning
the connection of any of them with those of other people, are quite
right in concluding that we have no reason to assert that any other
person ever did have any particular thought or perception whatever. I
think that the words of this conclusion, understood in their natural
meaning, express precisely what the premiss asserts. We need not,
indeed, conclude, as many of these philosophers are inclined to do,
that, because we have no reason for believing in the existence of other
people, it is therefore highly doubtful whether they do exist. The
philosophers who advocate this opinion commonly refute themselves by
assigning the existence of other people as part of their reason for
believing that it is very doubtful whether any other people exist. That
for which we have no reason may, nevertheless, be certainly true. And,
indeed, one of the philosophers who hold most clearly and expressly
that we do know not only the existence of other people but also that
of material objects, is also one of those who deny most emphatically
that our own observations can give any reason for believing either
in the one or in the other. I refer to Thomas Reid. Reid, indeed,
allows himself to use not only the word "observe," but even the word
"perceive," in that wide sense in which it might be said that we
observe or perceive the thoughts and feelings of others: and I think
that the fact that he uses the words in this sense, has misled him into
thinking that his view is more plausible and more in accordance with
Common Sense than it really is: by using the words in this sense he is
able to plead that "observation" really does give a reason for some of
those generalisations, for which Common Sense holds that "observation"
(in a narrower sense) does give a reason. But with regard to what we
observe or perceive, in the strict sense to which 1 am confining those
words, he asserts quite explicitly that it gives us no reason either
for believing in the existence of material objects or for believing
in the existence of other minds. Berkeley, he says, has proved
incontrovertibly that it gives us no reason for the one, and Hume that
it gives us no reason for the other.
Now these philosophers may be right in holding this. It may, perhaps,
be true that, in this sense, my own observations give me no reason
whatever for believing that any other person ever has or will perceive
anything like or unlike what I perceive. But I think it is desirable
we should realise how paradoxical are the consequences which must be
admitted, if this is true. It must then be admitted that the very
large part of our knowledge, which we suppose to have some basis in
experience, is by no means based upon experience, in the sense, and
to the extent, which we suppose. We do for instance, commonly suppose
that there is some basis in experience for the assertion that some
people, whom we call Germans, use one set of words to express much the
same meaning which we express by using a different set of words. But,
if this view be correct, we must admit that no person's experience
gives him any reason whatever for supposing that, when he hears certain
words, any one else has ever heard or thought of the same words, or
meant anything by them. The view admits, indeed, that I do know that
when I hear certain words, somebody else has generally had thoughts
more or less similar to those which I suppose him to have had: but it
denies that my own observations could ever give me the least reason
for supposing that this is so. It admits that my own observations may
give me reason for supposing that _if_ anyone has ever had perceptions
like mine in some respects, he will also have had other perceptions
like others of mine: but it denies that they give me any reason for
supposing that any one else has had a perception like one of mine. It
admits that my own observations may give me reason for supposing that
certain perceptions and thoughts in _one_ person (_if_ they exist) will
be followed or preceded by certain other perceptions and thoughts in
that person: but it denies that they give me any reason whatever for
_any_ similar generalisation concerning the connection of a certain
kind of perception in one person with a certain kind of perception in
another. It admits that I should not have certain perceptions, which
I do have, unless someone else had had certain other perceptions; but
it denies that my own observations can give me any reason for saying
so--for saying that I should not have had this perception, unless
someone else had had that. No observations of mine, it holds, can ever
render it probable that such a generalisation is true; no observation
of mine can ever confirm or verify such a generalisation. If we are to
say that any such generalisation whatever is based upon observation,
we can only mean, what Reid means, that it is based on a series of
assumptions. When I observe this particular thing, I assume that _that_
particular thing, which I do not observe, exists; when I observe
another particular thing, I again assume that a second particular
thing, which I do not observe, exists; when I observe a third
particular thing, I again assume that a third particular thing, which I
do not observe, exists. These assumed facts--the assumed fact that one
observation of mine is accompanied by the existence of one particular
kind of thing, and that another observation of mine is accompanied by
the existence of a different particular kind of thing, will then give
me a reason for different generalisations concerning the connection of
different perceptions of mine with different external objects--objects
which I do not perceive. But (it is maintained) nothing but a mass of
such assumptions will give me a reason for any such generalisation.
Now I think it must be admitted that there is something paradoxical
in such a view. I think it may be admitted that, in holding it, the
philosopher of Common Sense departs from Common Sense at least as far
in one direction as his opponents had done in another. But I think
that there is some excuse for those who hold it: I think that, in one
respect, they are more in the right than those who do not hold it--than
those who hold that my own observations do give me a reason for
believing in the existence of other people. For those who hold that my
observations do give me a reason, have, I believe, universally supposed
that the reason lies in a part of my observations, in which no such
reason is to be found. This is why I have chosen to ask the question:
_What_ reason do my observations give me for believing that any other
person has any particular perceptions or beliefs? I wish to consider
_which_ among the things which I observe will give such a reason. For
this is a question to which no answer, that I have ever seen, appears
to me to be correct. Those who have asked it have, so far as I know,
answered it _either_ by denying that my observations give me any reason
_or_ by pointing to a part of my observations, which, as it seems to
me, really do give none. Those who deny are, it seems to me, right in
holding that the reason given by those who affirm is no reason. And
their correct opinion on this point will, I think, partly serve to
explain their denial. They have supposed that if our observations give
us any reason at all for asserting the existence of other people, that
reason must lie where it has been supposed to lie by those who hold
that they do give a reason. And then, finding that this assigned reason
is no reason, they have assumed that there is no other.
I am proposing then to ask: Which among the observations, which I make,
and which (as we commonly suppose) are similar in kind to those which
all or almost all men make, will give a reason for supposing that the
existence of any of them is generally connected with the existence of
certain kinds of perception or belief in other people? And in order to
answer this question, it is obvious we must first consider two others.
We must consider, in the first place: Of what nature must observations
be, if they are to give a reason for any generalisation asserting that
the existence of one kind of thing is generally connected with that of
another? And we must consider in the second place: What kinds of things
do we observe?
Now to the first of these questions I am not going to attempt to give
a complete answer. The question concerning the rules of Inductive
Logic, which is the question at issue, is an immensely difficult and
intricate question. And I am not going to attempt to say, what kind of
observations are _sufficient_ to justify a generalisation. But it is
comparatively easy to point out that a certain kind of observations are
_necessary_ to justify a generalisation: and this is all that I propose
to do. I wish to point out certain conditions which observations must
satisfy, if they are to justify a generalisation; without in any way
implying that all observations which do satisfy these conditions,
_will_ justify a generalisation. The conditions, I shall mention, are
ones which are certainly _not_ sufficient to justify a generalisation;
but they are, I think, conditions, without which no generalisation can
be justified. If a particular kind of observations do _not_ satisfy
these conditions, we can say with certainty that those observations
give us _no_ reason for believing in the existence of other people;
though, with regard to observations which _do_ satisfy them, we shall
only be able to say that they _may_ give a reason.
What conditions, then, must observations satisfy, if they are to
justify a generalisation? Let us suppose that the generalisation to
be justified is one which asserts that the existence of a kind of
object, which we will call A, is generally preceded, accompanied, or
followed by the existence of a kind of object, which we call B. A, for
instance, might be the hearing of a certain word by one person, and B
the thought of that which we call the meaning of the word, in another
person; and the generalisation to be justified might be that when one
person hears a word, not spoken by himself, someone else has generally
thought of the meaning of that word. What must I have observed, if the
generalisation that the existence of A is generally preceded by the
existence of B, is to be justified by my observations? One first point,
I think, is plain. I must have observed both some object, which is in
some respects like A, and which I will call _α_, and also some object
in some respects like B which I will call _β_: I must have observed
both _α_ and _β_, and also I must have observed _β_ preceding _α._
This, at least, I must have observed. But I do not pretend to say _how_
like _α_ and _β_ must be to A and B; nor do I pretend to say how often
I must have observed _β_ preceding _α_, although it is generally held
that I must have observed this more than once. These are questions,
which would have to be discussed if we were trying to discover what
observations were _sufficient_ to justify the generalisation that the
existence of A is generally preceded by that of B. But I am only
trying to lay down the minimum which is _necessary_ to justify this
generalisation; and therefore I am content to say that we must have
observed something more or less like B preceding something more or less
like A, at least once.
But there is yet another minimum condition. If my observation of _β_
preceding _α_ is to justify the generalisation that the _existence_ of
A is generally preceded by the _existence_ of B, it is plain, I think,
that both the _β_ and the _α,_ which I observed, must have _existed_
or been _real_; and that also the existence of _β_ must _really_ have
preceded that of _α_. It is plain that if, when I observed _α_ and
_β_, _α_ existed but _β_ did not, this observation could give me no
reason to suppose that on another occasion when A existed, _β_ _would_
exist. Or again, if, when I observed _β_ preceding _α_, both _β_ and
_α_ existed, but the existence of _β_ did not _really_ precede that of
α, but, on the contrary, followed it, this observation could certainly
give me no reason to suppose that, in general, the existence of A was
_preceded_ by the existence of B. Indeed this condition that what is
observed must have been _real_ might be said to be included in the very
meaning of the word "observation." We should, in this connection, say
that we had _not_ observed _β_ preceding _α,_ unless _β_ and _α_ were
both real, and _β_ had really preceded _α._ If I say "I have _observed_
that, on one occasion, my hearing of the word 'moon' was followed by
my imagining a luminous silvery disc," I commonly mean to include in
my statement the assertion that I did, on that occasion, really hear
the word "moon," and really did have a visual image of a luminous
disc, and that my perception was really followed by my imagination.
If it were proved to me that this had not really happened, I should
admit that I had not really observed it. But though this condition
that, if observation is to give reason for a generalisation, what is
observed must be real, may thus be said to be implied in the very
word "observation," it was necessary for me to mention the condition
explicitly. It was necessary, because, as I shall presently show,
we do and must also use the word "observation" in a sense in which
the assertion "I observe A" by no means includes the assertion "A
exists"--in a sense in which it _may_ be true that though I did observe
A, yet A did _not_ exist.