SOCRATES: Well, may not a man 'possess' and yet not 'have' knowledge in the sense of which I am speaking? As you may suppose a man to have caught wild birds--doves or any other birds--and to be keeping them in an aviary which he has constructed at home; we might say of him in one sense, that he always has them because he possesses them, might we not? THEAETETUS: Yes. SOCRATES: And yet, in another sense, he has none of them; but they are in his power, and he has got them under his hand in an enclosure of his own, and can take and have them whenever he likes;--he can catch any which he likes, and let the bird go again, and he may do so as often as he pleases. THEAETETUS: True. SOCRATES: Once more, then, as in what preceded we made a sort of waxen figment in the mind, so let us now suppose that in the mind of each man there is an aviary of all sorts of birds--some flocking together apart from the rest, others in small groups, others solitary, flying anywhere and everywhere. THEAETETUS: Let us imagine such an aviary--and what is to follow? SOCRATES: We may suppose that the birds are kinds of knowledge, and that when we were children, this receptacle was empty; whenever a man has gotten and detained in the enclosure a kind of knowledge, he may be said to have learned or discovered the thing which is the subject of the knowledge: and this is to know. THEAETETUS: Granted. SOCRATES: And further, when any one wishes to catch any of these knowledges or sciences, and having taken, to hold it, and again to let them go, how will he express himself?--will he describe the 'catching' of them and the original 'possession' in the same words? I will make my meaning clearer by an example:--You admit that there is an art of arithmetic? THEAETETUS: To be sure. SOCRATES: Conceive this under the form of a hunt after the science of odd and even in general. THEAETETUS: I follow. SOCRATES: Having the use of the art, the arithmetician, if I am not mistaken, has the conceptions of number under his hand, and can transmit them to another. THEAETETUS: Yes. SOCRATES: And when transmitting them he may be said to teach them, and when receiving to learn them, and when receiving to learn them, and when having them in possession in the aforesaid aviary he may be said to know them. THEAETETUS: Exactly. SOCRATES: Attend to what follows: must not the perfect arithmetician know all numbers, for he has the science of all numbers in his mind? THEAETETUS: True. SOCRATES: And he can reckon abstract numbers in his head, or things about him which are numerable? THEAETETUS: Of course he can. SOCRATES: And to reckon is simply to consider how much such and such a number amounts to? THEAETETUS: Very true. SOCRATES: And so he appears to be searching into something which he knows, as if he did not know it, for we have already admitted that he knows all numbers;--you have heard these perplexing questions raised? THEAETETUS: I have.