Plato’s Theory of Knowledge: the Theaetetus and the Sophist of Plato, translated with a running commentary by Francis Macdonald Cornford, International Library of Psychology, Philosophy and Scientific Method, Routledge & Kegan Paul, 19351

Theaetetus [Plat. Theaet.]. Platonis Opera. Perseus Digital Library Project

p. 121, 191B-E:

SOCR. We must, in fact, put the case in a different way. Perhaps the barrier will yield somewhere, though it may defy our efforts. Anyhow, we are in such straits that we must turn every argument over and put it to the test. Now, is there anything in this? Is it possible to become acquainted with something one did not know before?

THEAT. Surely.

SOCR. And the process can be repeated with one thing after another?

THEAT. Of course.

SOCR. Imagine, then, for the sake of argument, that our minds contain a block of wax, which in this or that individual may be larger or smaller, and composed of wax that is comparatively pure or muddy, and harder in some, softer in others, and sometimes of just the right consistency.

THEAT. Very well.

SOCR. Let us call it the gift of the Muses’ mother, Memory,2 and say that whenever we wish to remember something we see or hear or conceive in our own minds, we hold this wax under the perceptions or ideas and imprint them on it as we might stamp the impression of a seal-ring. Whatever is so imprinted we remember and know so long as the image remains; whatever is rubbed out or has not succeeded in leaving an impression we have forgotten and do not know.

THEAT. So be it.

pp. 132-134, 197C-198D:

SOCR. ‘Having’ seems to me different from ‘possessing’. If a man has bought a coat and owns it, but is not wearing it, we should say he possesses it without having it about him.

THEAT. True.

SOCR. Now consider whether knowledge is a thing you can possess in that way without having it about you, like a man who has caught some wild birds — pigeons or what not — and keeps them in an aviary he has made for them at home. In a sense, of course, we might say he ‘has’ them all the time inasmuch as he possesses them, mightn’t we?


SOCR. But in another sense he ‘has’ none of them, though he has got control of them, now that he has made them captive in an enclosure of his own; he can take and have hold of them whenever he likes by catching any bird he chooses, and let them go again; and it is open to him to do that as often as he pleases.

THEAT. That is so.

SOCR. Once more then, just as a while ago we imagined a sort of waxen block in our minds, so now let us suppose that every mind contains a kind of aviary stocked with birds of every sort, some in flocks apart from the rest, some in small groups, and some solitary, flying in any direction among them all.

THEAT. Be it so. What follows?

SOCR. When we are babies we must suppose this receptacle empty, and take the birds to stand for pieces of knowledge. Whenever a person acquires any piece of knowledge and shuts it up in his enclosure, we must say he has learnt or discovered the thing of which this is the knowledge, and that is what ‘knowing’ means.

THEAT. Be it so.

SOCR. Now think of him hunting once more for any piece of knowledge that he wants, catching and holding it, and letting it go again. In what terms are we to describe that — the same that we used of the original process of acquisition, or different ones? An illustration may help you to see what I mean. There is a science you call ‘arithmetic’.


SOCR. Conceive that, then, as a chase after pieces of knowledge about all the numbers, odd or even.

THEAT. I will.

SOCR. That, I take it, is the science in virtue of which a man has in his control pieces of knowledge about numbers and can hand them over to someone else.


SOCR. And when he hands them over, we call it ‘teaching’, and when the other takes them from him, that is ‘learning’, and when he has them in the sense of possessing them in that aviary of his, that is ‘knowing’.

THEAT. Certainly.

SOCR. Now observe what follows. The finished arithmetician knows all numbers, doesn’t he? There is no number the knowledge of which is not in his mind.

THEAT. Naturally.

SOCR. And such a person may sometimes count either the numbers themselves in his own head or some set of external things that have a number.

THEAT. Of course.

SOCR. And by counting we shall mean simply trying to find out what some particular number amounts to ?


SOCR. It appears, then, that the man who, as we admitted, knows every number, is trying to find out what he knows as if he had no knowledge of it. No doubt you sometimes hear puzzles of that sort debated.

THEAT. Indeed I do.

SOCR. Well, our illustration from hunting pigeons and getting possession of them will enable us to explain that the hunting occurs in two ways : first, before you possess your pigeon in order to have possession of it; secondly, after getting possession of it, in order to catch and hold in your hand what you have already possessed for some time. In the same way, if you have long possessed pieces of knowledge about things you have learnt and know, it is still possible to get to know the same things again, by the process of recovering the knowledge of some particular thing and getting hold of it. It is knowledge you have possessed for some time, but you had not got it handy in your mind.

THEAT. True.


  2. Theoi Project:

    MNEMOSYNE was the Titan goddess of memory and remembrance and the inventress of language and words.

    As a Titan daughter of Ouranos (Uranus, Heaven), Mnemosyne was also a goddess of time. She represented the rote memorisation required to preserve the stories of history and the sagas of myth before the introduction of writing. In this role she was the mother of the Mousai (Muses) who were originally patron goddesses of poets of the oral tradition.