Bertrand Russell: The Problems of Philosophy
Knowledge By Acquaintance And Knowledge By Description
In the preceding chapter we saw that there are two sorts of knowledge:
knowledge of things, and knowledge of truths. In this chapter we shall
be concerned exclusively with knowledge of things, of which in turn we
shall have to distinguish two kinds. Knowledge of things, when it is of
the kind we call knowledge by acquaintance, is essentially simpler
than any knowledge of truths, and logically independent of knowledge of
truths, though it would be rash to assume that human beings ever, in fact,
have acquaintance with things without at the same time knowing some truth
about them. Knowledge of things by description, on the contrary,
always involves, as we shall find in the course of the present chapter,
some knowledge of truths as its source and ground. But first of all we
must make dear what we mean by 'acquaintance' and what we mean by 'description'.
We shall say that we have acquaintance with anything of which
we are directly aware, without the intermediary of any process of inference
or any knowledge of truths. Thus in the presence of my table I am acquainted
with the sense-data that make up the appearance of my table -- its colour,
shape, hardness, smoothness, etc.; all these are things of which I am immediately
conscious when I am seeing and touching my table. The particular shade
of colour that I am seeing may have many things said about it -- I may
say that it is brown, that it is rather dark, and so on. But such statements,
though they make me know truths about the colour, do not make me
know the colour itself any better than I did before: so far a concerns
knowledge of the colour itself, as opposed to knowledge of truths about
it, I know the colour perfectly and completely when I see it, and no further
knowledge of it itself is even theoretically possible. Thus the sense-data
which make up the appearance of my table are things with which I have acquaintance,
things immediately known to me just as they are.
My knowledge of the table as a physical object, on the contrary, is
not direct knowledge. Such as it is, it is obtained through acquaintance
with the sense-data that make up the appearance of the table. We have seen
that it is possible, without absurdity, to doubt whet there is a table
at all, whereas it is not possible to doubt the sense-data. My knowledge
of the table is of the kind which we shall call 'knowledge by description'.
The table is 'the physical object which causes such-and-such sense-data'.
This describes the table by means of the sense-data. In order to
know anything at all about the table, we must know truths connecting it
with things with which we have acquaintance: we must know that 'such-and-such
sense-data are caused by a physical object'. There is no state of mind
in which we are directly aware of the table; all our knowledge of the table
is really knowledge of truths, and the actual thing which is the
table is not, strictly speaking, known to us at all. We know a description
and we know that there is just one object to which this description applies,
though the object itself is not directly known to us. In such a case, we
say that our knowledge of the object is knowledge by description.
All our knowledge, both knowledge of things and knowledge of truths,
rests upon acquaintance as its foundation. It is therefore important to
consider what kinds of things there are with which we have acquaintance.
Sense-data, as we have already seen, are among the things with which
we are acquainted; in fact, they supply the most obvious and striking example
of knowledge by acquaintance. But if they were the sole example, our knowledge
would be very much more restricted than it is. We should only know what
is now present to our senses: we could not know anything about the past
-- not even that there was a past -- nor could we know any truths about
our sense-data, for all knowledge of truths, as we shall show, demands
acquaintance with things which are of an essentially different character
from sense-data, the things which are sometimes called 'abstract ideas',
but which we shall call 'universals'. We have therefore to consider acquaintance
with other things besides sense-data if we are to obtain any tolerably
adequate analysis of our knowledge.
The first extension beyond sense-data to be considered is acquaintance
by memory. It is obvious that we often remember what we have seen
or heard or had otherwise present to our senses, and that in such cases
we are still immediately aware of what we remember, in spite of the fact
that it appears as past and not as present. This immediate knowledge by
memory is the source of all our knowledge concerning the past: without
it, there could be no knowledge of the past by inference we should never
know that there was anything past to be inferred.
The next extension to be considered is acquaintance by introspection.
We are not only aware of things, but we are often aware of being aware
of them. When I see the sun, I am often aware of my seeing the sun; thus
'my seeing the sun' is an object with which I have acquaintance. When I
desire food, I may be aware of my desire for food; thus 'my desiring food'
is an object with which I am acquainted. Similarly we may be aware of our
feeling pleasure or pain, and generally of the events which happen in our
minds. This kind of acquaintance, which may be called self-consciousness,
is the source of all our knowledge of mental things. It is obvious that
it is only what goes on in our own minds that can be thus known immediately.
What goes on in the minds of others is known to us through our perception
of their bodies, that is, the sense-data in us which are associated with
their bodies. But for our acquaintance with the contents of our own minds,
we should be unable to imagine the minds of others, and therefore we could
never arrive at the knowledge that they have minds. It seems natural to
suppose that self-consciousness is one of the things that distinguish men
from animals: animals, we may suppose, though they have acquaintance with
sense-data, never become aware of this acquaintance. I do not mean that
they doubt whether they exist, but that they have never become conscious
of the fact that they have sensations and feelings, nor therefore of the
fact that they, the subjects of their sensations and feelings, exist.
We have spoken of acquaintance with the contents of our minds as self-consciousness,
but it is not, of course, consciousness of our self: it is consciousness
of particular thoughts and feelings. The question whether we are also acquainted
with our bare selves, as opposed to particular thoughts and feelings, is
a very difficult one, upon which it would be rash to speak positively.
When we try to look into ourselves we always seem to come upon some particular
thought or feeling, and not upon the 'I' which has the thought or feeling.
Nevertheless there are some reasons for thinking that we are acquainted
with the 'I', though the acquaintance is hard to disentangle from other
things. To make clear what sort of reason there is, let us consider for
a moment what our acquaintance with particular thoughts really involves.
When I am acquainted with 'my seeing the sun', it seems plain that I
am acquainted with two different things in relation to each other. On the
one hand there is the sense-datum which represents the sun to me, on the
other hand there is that which sees this sense-datum. All acquaintance,
such as my acquaintance with the sense-datum which represents the sun,
seems obviously a relation between the person acquainted and the object
with which the person is acquainted. When a case of acquaintance is one
with which I can be acquainted (as I am acquainted with my acquaintance
with the sense-datum representing the sun), it is plain that the person
acquainted is myself. Thus, when I am acquainted with my seeing the sun,
the whole fact with which I am acquainted is 'Self-acquainted-with-sense-datum'.
Further, we know the truth 'I am acquainted with this sense-datum'.
It is hard to see how we could know this truth, or even understand what
is meant by it, unless we were acquainted with something which we call
'I'. It does not seem necessary to suppose that we are acquainted with
a more or less permanent person, the same to-day as yesterday, but it does
seem as though we must be acquainted with that thing, whatever its nature,
which sees the sun and has acquaintance with sense-data. Thus, in some
sense it would seem we must be acquainted with our Selves as opposed to
our particular experiences. But the question is difficult, and complicated
arguments can be adduced on either side. Hence, although acquaintance with
ourselves seems probably to occur, it is not wise to assert that
it undoubtedly does occur.
We may therefore sum up as follows what has been said concerning acquaintance
with things that exist. We have acquaintance in sensation with the data
of the outer senses, and in introspection with the data of what may be
called the inner sense -- thoughts, feelings, desires, etc.; we have acquaintance
in memory with things which have been data either of the outer senses or
of the inner sense. Further, it is probable, though not certain, that we
have acquaintance with Self, as that which is aware of things or has desires
In addition to our acquaintance with particular existing things, we
also have acquaintance with what we shall call universals, that
is to say, general ideas such as whiteness, diversity, brotherhood,
and so on. Every complete sentence must contain at least one word which
stands for a universal, since all verbs have a meaning which is universal.
We shall return to universals later on, in Chapter IX; for the present,
it is only necessary to guard against the supposition that whatever we
can be acquainted with must be something particular and existent. Awareness
of universals is called conceiving, and a universal of which we
are aware is called a concept.
It will be seen that among the objects with which we are acquainted
are not included physical objects (as opposed to sense-data), nor other
people's minds. These things are known to us by what I call 'knowledge
by description', which we must now consider.
By a 'description' I mean any phrase of the form 'a so-and-so' or 'the
so-and-so'. A phrase of the form 'a so-and-so' I shall call an 'ambiguous'
description; a phrase of the form 'the so-and-so' (in the singular) I shall
call a 'definite' description. Thus 'a man' is an ambiguous description,
and 'the man with the iron mask' is a definite description. There are various
problems connected with ambiguous descriptions, but I pass them by, since
they do not directly concern the matter we are discussing, which is the
nature of our knowledge concerning objects in cases where we know that
there is an object answering to a definite description, though we are not
acquainted with any such object. This is a matter which is concerned exclusively
with definite descriptions. I shall therefore, in the sequel, speak simply
of 'descriptions' when I mean 'definite descriptions'. Thus a description
will mean any phrase of the form 'the so-and-so' in the singular.
We say that an object is 'known by description' when we know that it
is 'the so-and-so', i.e. when we know that there is one object, and no
more, having a certain property; and it will generally be implied that
we do not have knowledge of the same object by acquaintance. We know that
the man with the iron mask existed, and many propositions are known about
him; but we do not know who he was. We know that the candidate who gets
the most votes will be elected, and in this case we are very likely also
acquainted (in the only sense in which one can be acquainted with some
one else) with the man who is, in fact, the candidate who will get most
votes; but we do not know which of the candidates he is, i.e. we do do
not know any proposition of the form 'A is the candidate who will get most
votes' where A is one of the candidates by name. We shall say that we have
'merely descriptive knowledge' of the so-and-so when, although we know
that the so-and-so exists, and although we may possibly be acquainted with
the object which is, in fact, the so-and-so, yet we do not know any proposition
'a is the so-and-so', where a is something with which we are acquainted.
When we say 'the so-and-so exists', we mean that there is just one object
which is the so-and-so. The proposition 'a is the so-and-so' means
that a has the property so-and-so, and nothing else has. 'Mr. A.
is the Unionist candidate for this constituency' means 'Mr. A. is a Unionist
candidate for this constituency, and no one else is'. 'The Unionist candidate
for this constituency exists' means 'some one is a Unionist candidate for
this constituency, and no one else is'. Thus, when we are acquainted with
an object which is the so-and-so, we know that the so-and-so exists; but
we may know that the so-and-so exists when we are not acquainted with any
object which we know to be the so-and-so, and even when we are not acquainted
with any object which, in fact, is the so-and-so.
Common words, even proper names, are usually really descriptions. That
is to say, the thought in the mind of a person using a proper name correctly
can generally only be expressed explicitly if we replace the proper name
by a description. Moreover, the description required to express the thought
will vary for different people, or for the same person at different times.
The only thing constant (so long as the name is rightly used) is the object
to which the name applies. But so long as this remains constant, the particular
description involved usually makes no difference to the truth or falsehood
of the proposition in which the name appears.
Let us take some illustrations. Suppose some statement made about Bismarck.
Assuming that there is such a thing as direct acquaintance with oneself,
Bismarck himself might have used his name directly to designate the particular
person with whom he was acquainted. In this case, if he made a judgement
about himself, he himself might be a constituent of the judgement. Here
the proper name has the direct use which it always wishes to have, as simply
standing for a certain object, and not for a description of the object.
But if a person who knew Bismarck made a judgement about him, the case
is different. What this person was acquainted with were certain sense-data
which he connected (rightly, we will suppose) with Bismarck's body. His
body, as a physical object, and still more his mind, were only known as
the body and the mind connected with these sense-data. That is, they were
known by description. It is, of course, very much a matter of chance which
characteristics of a man's appearance will come into a friend's mind when
he thinks of him; thus the description actually in the friend's mind is
accidental. The essential point is that he knows that the various descriptions
all apply to the same entity, in spite of not being acquainted with the
entity in question.
When we, who did not know Bismarck, make judgement about him, the description
in our minds will probably be some more or less vague mass of historical
knowledge -- far more, in most cases, than is required to identify him.
But, for the sake of illustration, let us assume that we think of him as
'the first Chancellor of the German Empire'. Here all the words are abstract
except 'German'. The word 'German' will, again, have different meanings
for different people. To some it will recall travels in Germany, to some
the look of Germany on the map, and so on. But if we are to obtain a description
which we know to be applicable, we shall be compelled, at some point, to
bring in a reference to a particular with which we are acquainted. Such
reference is involved in any mention of past, present, and future (as opposed
to definite dates), or of here and there, or of what others have told us.
Thus it would seem that, in some way or other, a description known to be
applicable to a particular must involve some reference to a particular
with which we are acquainted, if our knowledge about the thing described
is not to be merely what follows logically from the description.
or example, 'the most long-lived of men' is a description involving only
universals, which must apply to some man, but we can make no judgements
concerning this man which involve knowledge about him beyond what the description
gives. If, however, we say, 'The first Chancellor of the German Empire
was an astute diplomatist', we can only be assured of the truth of our
judgement in virtue of something with which we are acquainted -- usually
a testimony heard or read. Apart from the information we convey to others,
apart from the fact about the actual Bismarck, which gives importance to
our judgement, the thought we really have contains the one or more particulars
involved, and otherwise consists wholly of concepts.
All names of places -- London, England, Europe, the Earth, the Solar
System -- similarly involve, when used, descriptions which start from some
one or more particulars with which we are acquainted. I suspect that even
the Universe, as considered by metaphysics, involves such a connexion with
particulars. In logic on the contrary, where we are concerned not merely
with what does exist, but with whatever might or could exist or be, no
reference to actual particulars is involved.
It would seem that, when we make a statement about something only known
by description, we often intend to make our statement, not in the
form involving the description, but about the actual thing described. That
is to say, when we say anything about Bismarck, we should like, if we could,
to make the judgement which Bismarck alone can make, namely, the judgement
of which he himself is a constituent. In this we are necessarily defeated,
since the actual Bismarck is unknown to us. But we know that there is an
object B, called Bismarck, and that B was an astute diplomatist. We can
thus describe the proposition we should like to affirm, namely,
'B was an astute diplomat', where B is the object which was Bismarck. If
we are describing Bismarck as 'the first Chancellor of the German Empire',
the proposition we should like to affirm may be described as 'the proposition
asserting, concerning the actual object which was the first Chancellor
of the German Empire, that this object an astute diplomatist'. What enables
us to communicate in spite of the varying descriptions we employ is that
we know there is a true proposition concerning the actual Bismarck, and
that however we may vary be description (so long as the description is
correct) the proposition described is still the same. This proposition,
which is described and is known to be true, is what interests us; but we
are not acquainted with the proposition itself, and do not know it,
though we know it is true.
It will be seen that there are various stages in the removal from acquaintance
with particulars: there is Bismarck to people who knew him; Bismarck to
those who only know of him through history; the man with the iron mask;
the longest-lived of men. These are progressively further removed from
acquaintance with particulars; the first comes as near to acquaintance
as is possible in regard to another person; in the second, we shall still
be said to know 'who Bismarck was'; in the third, we do not know who was
the man with the iron mask, though we can know many propositions about
him which are not logically deducible from the fact that he wore an iron
mask; in the fourth, finally, we know nothing beyond what is logically
deducible from the definition of the man. There is a similar hierarchy
in the region of universals. Many universals like many particulars, are
only known to us by description. But here, as in the case of particulars,
knowledge concerning what is known by description is ultimately reducible
to knowledge concerning what is known by acquaintance.
The fundamental principle in the analysis of propositions containing
descriptions is this: Every proposition which we can understand must
be composed wholly of constituents with which we are acquainted.
We shall not at this stage attempt to answer all the objections which
may be urged against this fundamental principle. For the present, we shall
merely point out that, in some way or other, it must be possible to meet
these objections, for it is scarcely conceivable that we can make a judgement
or entertain a supposition without knowing what it is that we are judging
or supposing about. We must attach some meaning to the words we
use, if we are to speak significantly and not utter mere noise; and the
meaning we attach to our words must be something with which we are acquainted.
Thus when, for example, we make a statement about Julius Caesar, it is
plain that Julius Caesar himself is not before our minds, since we are
not acquainted with him. We have in mind some description of Julius
Caesar: 'the man who was assassinated on the Ides of March', 'the founder
of the Roman Empire', or, merely 'the man whose name was Julius Caesar'.
(In this last description, Julius Caesar is a noise or shape with
which we are acquainted.) Thus our statement does not mean quite what it
seems to mean, but means something involving, instead of Julius Caesar,
some description of him which is composed wholly of particulars and universals
with which we are acquainted.
The chief importance of knowledge by description is that it enables
us to pass beyond the limits of our experience. In spite of the fact that
we can only know truths which are wholly composed of terms which we have
experienced in acquaintance, we can yet have knowledge by description of
things which we have never experienced. In view of the very narrow range
of our immediate experience, this result is vital, and until it is understood,
much of our knowledge must remain mysterious and therefore doubtful.