SOCRATES: And that which he does not know will sometimes not be perceived by him and sometimes will be perceived and only perceived? THEAETETUS: That is also true. SOCRATES: See whether you can follow me better now: Socrates can recognize Theodorus and Theaetetus, but he sees neither of them, nor does he perceive them in any other way; he cannot then by any possibility imagine in his own mind that Theaetetus is Theodorus. Am I not right? THEAETETUS: You are quite right. SOCRATES: Then that was the first case of which I spoke. THEAETETUS: Yes. SOCRATES: The second case was, that I, knowing one of you and not knowing the other, and perceiving neither, can never think him whom I know to be him whom I do not know. THEAETETUS: True. SOCRATES: In the third case, not knowing and not perceiving either of you, I cannot think that one of you whom I do not know is the other whom I do not know. I need not again go over the catalogue of excluded cases, in which I cannot form a false opinion about you and Theodorus, either when I know both or when I am in ignorance of both, or when I know one and not the other. And the same of perceiving: do you understand me? THEAETETUS: I do. SOCRATES: The only possibility of erroneous opinion is, when knowing you and Theodorus, and having on the waxen block the impression of both of you given as by a seal, but seeing you imperfectly and at a distance, I try to assign the right impression of memory to the right visual impression, and to fit this into its own print: if I succeed, recognition will take place; but if I fail and transpose them, putting the foot into the wrong shoe--that is to say, putting the vision of either of you on to the wrong impression, or if my mind, like the sight in a mirror, which is transferred from right to left, err by reason of some similar affection, then 'heterodoxy' and false opinion ensues. THEAETETUS: Yes, Socrates, you have described the nature of opinion with wonderful exactness. SOCRATES: Or again, when I know both of you, and perceive as well as know one of you, but not the other, and my knowledge of him does not accord with perception--that was the case put by me just now which you did not understand. THEAETETUS: No, I did not. SOCRATES: I meant to say, that when a person knows and perceives one of you, his knowledge coincides with his perception, he will never think him to be some other person, whom he knows and perceives, and the knowledge of whom coincides with his perception--for that also was a case supposed. THEAETETUS: True. SOCRATES: But there was an omission of the further case, in which, as we now say, false opinion may arise, when knowing both, and seeing, or having some other sensible perception of both, I fail in holding the seal over against the corresponding sensation; like a bad archer, I miss and fall wide of the mark--and this is called falsehood. THEAETETUS: Yes; it is rightly so called.