Chapter V. Knowledge by Acquaintance and Knowledge by Description

by Bertrand Russell

　　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 beconcerned exclusively with knowledge of things, of which in turn we shallhave to distinguish two kinds. Knowledge of things, when it is of the kindwe call knowledge by acquaintance, is essentially simpler than anyknowledge of truths, and logically independent of knowledge of truths,though it would be rash to assume that human beings ever, in fact, haveacquaintance with things without at the same time knowing some truth aboutthem. Knowledge of things by description, on the contrary, alwaysinvolves, as we shall find in the course of the present chapter, someknowledge of truths as its source and ground. But first of all we mustmake clear what we mean by 'acquaintance' and what we mean by'description'.

　　We shall say that we have acquaintance with anything of which weare directly aware, without the intermediary of any process of inferenceor any knowledge of truths. Thus in the presence of my table I amacquainted with the sense-data that make up the appearance of my table—itscolour, shape, hardness, smoothness, etc.; all these are things of which Iam immediately conscious when I am seeing and touching my table. Theparticular shade of colour that I am seeing may have many things saidabout it—I may say that it is brown, that it is rather dark, and soon. 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 faras concerns knowledge of the colour itself, as opposed to knowledge oftruths about it, I know the colour perfectly and completely when I see it,and no further knowledge of it itself is even theoretically possible. Thusthe sense-data which make up the appearance of my table are things withwhich I have acquaintance, things immediately known to me just as theyare.

　　My knowledge of the table as a physical object, on the contrary, is notdirect knowledge. Such as it is, it is obtained through acquaintance withthe sense-data that make up the appearance of the table. We have seen thatit is possible, without absurdity, to doubt whether there is a table atall, whereas it is not possible to doubt the sense-data. My knowledge ofthe 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 knowanything at all about the table, we must know truths connecting it withthings with which we have acquaintance: we must know that 'such-and-suchsense-data are caused by a physical object'. There is no state of mind inwhich we are directly aware of the table; all our knowledge of the tableis really knowledge of truths, and the actual thing which is the table isnot, strictly speaking, known to us at all. We know a description, and weknow 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, wesay that our knowledge of the object is knowledge by description.

　　All our knowledge, both knowledge of things and knowledge of truths, restsupon acquaintance as its foundation. It is therefore important to considerwhat kinds of things there are with which we have acquaintance.

　　Sense-data, as we have already seen, are among the things with which weare acquainted; in fact, they supply the most obvious and striking exampleof knowledge by acquaintance. But if they were the sole example, ourknowledge would be very much more restricted than it is. We should onlyknow what is now present to our senses: we could not know anything aboutthe past—not even that there was a past—nor could we know anytruths about our sense-data, for all knowledge of truths, as we shallshow, demands acquaintance with things which are of an essentiallydifferent character from sense-data, the things which are sometimes called'abstract ideas', but which we shall call 'universals'. We have thereforeto consider acquaintance with other things besides sense-data if we are toobtain any tolerably adequate analysis of our knowledge.

　　The first extension beyond sense-data to be considered is acquaintance bymemory. It is obvious that we often remember what we have seen orheard or had otherwise present to our senses, and that in such cases weare still immediately aware of what we remember, in spite of the fact thatit appears as past and not as present. This immediate knowledge by memoryis the source of all our knowledge concerning the past: without it, therecould be no knowledge of the past by inference, since we should never knowthat 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 ofthem. When I see the sun, I am often aware of my seeing the sun; thus 'myseeing the sun' is an object with which I have acquaintance. When I desirefood, I may be aware of my desire for food; thus 'my desiring food' is anobject with which I am acquainted. Similarly we may be aware of ourfeeling pleasure or pain, and generally of the events which happen in ourminds. This kind of acquaintance, which may be called self-consciousness,is the source of all our knowledge of mental things. It is obvious that itis 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 perceptionof their bodies, that is, through the sense-data in us which areassociated with their bodies. But for our acquaintance with the contentsof our own minds, we should be unable to imagine the minds of others, andtherefore we could never arrive at the knowledge that they have minds. Itseems natural to suppose that self-consciousness is one of the things thatdistinguish men from animals: animals, we may suppose, though they haveacquaintance with sense-data, never become aware of this acquaintance. Ido not mean that they doubt whether they exist, but that they havenever become conscious of the fact that they have sensations and feelings,nor therefore of the fact that they, the subjects of their sensations andfeelings, 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 isconsciousness of particular thoughts and feelings. The question whether weare also acquainted with our bare selves, as opposed to particularthoughts and feelings, is a very difficult one, upon which it would berash to speak positively. When we try to look into ourselves we alwaysseem to come upon some particular thought or feeling, and not upon the 'I'which has the thought or feeling. Nevertheless there are some reasons forthinking that we are acquainted with the 'I', though the acquaintance ishard to disentangle from other things. To make clear what sort of reasonthere is, let us consider for a moment what our acquaintance withparticular thoughts really involves.

　　When I am acquainted with 'my seeing the sun', it seems plain that I amacquainted with two different things in relation to each other. On the onehand there is the sense-datum which represents the sun to me, on the otherhand there is that which sees this sense-datum. All acquaintance, such asmy acquaintance with the sense-datum which represents the sun, seemsobviously a relation between the person acquainted and the object withwhich the person is acquainted. When a case of acquaintance is one withwhich I can be acquainted (as I am acquainted with my acquaintance withthe sense-datum representing the sun), it is plain that the personacquainted 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 ishard to see how we could know this truth, or even understand what is meantby it, unless we were acquainted with something which we call 'I'. It doesnot seem necessary to suppose that we are acquainted with a more or lesspermanent person, the same to-day as yesterday, but it does seem as thoughwe must be acquainted with that thing, whatever its nature, which sees thesun and has acquaintance with sense-data. Thus, in some sense it wouldseem we must be acquainted with our Selves as opposed to our particularexperiences. But the question is difficult, and complicated arguments canbe adduced on either side. Hence, although acquaintance with ourselvesseems probably to occur, it is not wise to assert that itundoubtedly does occur.

　　We may therefore sum up as follows what has been said concerningacquaintance with things that exist. We have acquaintance in sensationwith the data of the outer senses, and in introspection with the data ofwhat may be called the inner sense—thoughts, feelings, desires,etc.; we have acquaintance in memory with things which have been dataeither 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 isaware of things or has desires towards things.

　　In addition to our acquaintance with particular existing things, we alsohave acquaintance with what we shall call universals, that is tosay, general ideas, such as whiteness, diversity, brotherhood,and so on. Every complete sentence must contain at least one word whichstands 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, itis only necessary to guard against the supposition that whatever we can beacquainted with must be something particular and existent. Awareness ofuniversals is called conceiving, and a universal of which we areaware is called a concept.

　　It will be seen that among the objects with which we are acquainted arenot included physical objects (as opposed to sense-data), nor otherpeople's minds. These things are known to us by what I call 'knowledge bydescription', which we must now consider.

　　By a 'description' I mean any phrase of the form 'a so-and-so' or 'theso-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) Ishall call a 'definite' description. Thus 'a man' is an ambiguousdescription, and 'the man with the iron mask' is a definite description.There are various problems connected with ambiguous descriptions, but Ipass them by, since they do not directly concern the matter we arediscussing, which is the nature of our knowledge concerning objects incases where we know that there is an object answering to a definitedescription, though we are not acquainted with any such object. This is amatter which is concerned exclusively with definite descriptions. I shalltherefore, in the sequel, speak simply of 'descriptions' when I mean'definite descriptions'. Thus a description will mean any phrase of theform 'the so-and-so' in the singular.

　　We shall say that an object is 'known by description' when we know that itis 'the so-and-so', i.e. when we know that there is one object, and nomore, having a certain property; and it will generally be implied that wedo not have knowledge of the same object by acquaintance. We know that theman 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 themost votes will be elected, and in this case we are very likely alsoacquainted (in the only sense in which one can be acquainted with some oneelse) 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 not know anyproposition of the form 'A is the candidate who will get most votes' whereA is one of the candidates by name. We shall say that we have 'merelydescriptive knowledge' of the so-and-so when, although we know that theso-and-so exists, and although we may possibly be acquainted with theobject which is, in fact, the so-and-so, yet we do not know anyproposition 'a is the so-and-so', where a is something withwhich we are acquainted.

　　When we say 'the so-and-so exists', we mean that there is just one objectwhich is the so-and-so. The proposition 'a is the so-and-so' meansthat a has the property so-and-so, and nothing else has. 'Mr. A. isthe Unionist candidate for this constituency' means 'Mr. A. is a Unionistcandidate for this constituency, and no one else is'. 'The Unionistcandidate for this constituency exists' means 'some one is a Unionistcandidate for this constituency, and no one else is'. Thus, when we areacquainted with an object which is the so-and-so, we know that theso-and-so exists; but we may know that the so-and-so exists when we arenot acquainted with any object which we know to be the so-and-so, and evenwhen we are not acquainted with any object which, in fact, is theso-and-so.

　　Common words, even proper names, are usually really descriptions. That isto say, the thought in the mind of a person using a proper name correctlycan generally only be expressed explicitly if we replace the proper nameby a description. Moreover, the description required to express thethought will vary for different people, or for the same person atdifferent times. The only thing constant (so long as the name is rightlyused) is the object to which the name applies. But so long as this remainsconstant, the particular description involved usually makes no differenceto the truth or falsehood of the proposition in which the name appears.

　　Let us take some illustrations. Suppose some statement made aboutBismarck. Assuming that there is such a thing as direct acquaintance withoneself, Bismarck himself might have used his name directly to designatethe particular person with whom he was acquainted. In this case, if hemade a judgement about himself, he himself might be a constituent of thejudgement. Here the proper name has the direct use which it always wishesto have, as simply standing for a certain object, and not for adescription of the object. But if a person who knew Bismarck made ajudgement about him, the case is different. What this person wasacquainted with were certain sense-data which he connected (rightly, wewill suppose) with Bismarck's body. His body, as a physical object, andstill more his mind, were only known as the body and the mind connectedwith these sense-data. That is, they were known by description. It is, ofcourse, very much a matter af chance which characteristics of a man'sappearance will come into a friend's mind when he thinks of him; thus thedescription actually in the friend's mind is accidental. The essentialpoint is that he knows that the various descriptions all apply to the sameentity, in spite of not being acquainted with the entity in question.

　　When we, who did not know Bismarck, make a judgement about him, thedescription in our minds will probably be some more or less vague mass ofhistorical knowledge—far more, in most cases, than is required toidentify him. But, for the sake of illustration, let us assume that wethink of him as 'the first Chancellor of the German Empire'. Here all thewords are abstract except 'German'. The word 'German' will, again, havedifferent meanings for different people. To some it will recall travels inGermany, to some the look of Germany on the map, and so on. But if we areto obtain a description which we know to be applicable, we shall becompelled, at some point, to bring in a reference to a particular withwhich we are acquainted. Such reference is involved in any mention ofpast, present, and future (as opposed to definite dates), or of here andthere, or of what others have told us. Thus it would seem that, in someway or other, a description known to be applicable to a particular mustinvolve some reference to a particular with which we are acquainted, ifour knowledge about the thing described is not to be merely what followslogically from the description. For example, 'the most long-livedof men' is a description involving only universals, which must apply tosome man, but we can make no judgements concerning this man which involveknowledge about him beyond what the description gives. If, however, wesay, 'The first Chancellor of the German Empire was an astutediplomatist', we can only be assured of the truth of our judgement invirtue of something with which we are acquainted—usually a testimonyheard or read. Apart from the information we convey to others, apart fromthe fact about the actual Bismarck, which gives importance to ourjudgement, the thought we really have contains the one or more particularsinvolved, and otherwise consists wholly of concepts.

　　All names of places—London, England, Europe, the Earth, the SolarSystem—similarly involve, when used, descriptions which start fromsome one or more particulars with which we are acquainted. I suspect thateven the Universe, as considered by metaphysics, involves such a connexionwith particulars. In logic, on the contrary, where we are concerned notmerely 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 bydescription, we often intend to make our statement, not in the forminvolving the description, but about the actual thing described. That isto say, when we say anything about Bismarck, we should like, if we could,to make the judgement which Bismarck alone can make, namely, the judgementof 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 anobject B, called Bismarck, and that B was an astute diplomatist. We canthus describe the proposition we should like to affirm, namely, 'Bwas an astute diplomatist', where B is the object which was Bismarck. Ifwe are describing Bismarck as 'the first Chancellor of the German Empire',the proposition we should like to affirm may be described as 'theproposition asserting, concerning the actual object which was the firstChancellor of the German Empire, that this object was an astutediplomatist'. What enables us to communicate in spite of the varyingdescriptions we employ is that we know there is a true propositionconcerning the actual Bismarck, and that however we may vary thedescription (so long as the description is correct) the propositiondescribed is still the same. This proposition, which is described and isknown to be true, is what interests us; but we are not acquainted with theproposition itself, and do not know it, though we know it is true.

　　It will be seen that there are various stages in the removal fromacquaintance with particulars: there is Bismarck to people who knew him;Bismarck to those who only know of him through history; the man with theiron mask; the longest-lived of men. These are progressively furtherremoved from acquaintance with particulars; the first comes as near toacquaintance as is possible in regard to another person; in the second, weshall still be said to know 'who Bismarck was'; in the third, we do notknow who was the man with the iron mask, though we can know manypropositions about him which are not logically deducible from the factthat he wore an iron mask; in the fourth, finally, we know nothing beyondwhat is logically deducible from the definition of the man. There is asimilar hierarchy in the region of universals. Many universals, like manyparticulars, are only known to us by description. But here, as in the caseof particulars, knowledge concerning what is known by description isultimately reducible to knowledge concerning what is known byacquaintance.

　　The fundamental principle in the analysis of propositions containingdescriptions is this: Every proposition which we can understand must becomposed wholly of constituents with which we are acquainted.

　　We shall not at this stage attempt to answer all the objections which maybe urged against this fundamental principle. For the present, we shallmerely point out that, in some way or other, it must be possible to meetthese objections, for it is scarcely conceivable that we can make ajudgement or entertain a supposition without knowing what it is that weare judging or supposing about. We must attach some meaning to thewords 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 areacquainted. Thus when, for example, we make a statement about JuliusCaesar, 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 ofJulius Caesar: 'the man who was assassinated on the Ides of March', 'thefounder of the Roman Empire', or, perhaps, merely 'the man whose name wasJulius Caesar'. (In this last description, Julius Caesar isa noise or shape with which we are acquainted.) Thus our statement doesnot mean quite what it seems to mean, but means something involving,instead of Julius Caesar, some description of him which is composed whollyof particulars and universals with which we are acquainted.

　　The chief importance of knowledge by description is that it enables us topass beyond the limits of our private experience. In spite of the factthat we can only know truths which are wholly composed of terms which wehave experienced in acquaintance, we can yet have knowledge by descriptionof things which we have never experienced. In view of the very narrowrange of our immediate experience, this result is vital, and until it isunderstood, much of our knowledge must remain mysterious and thereforedoubtful.