er' in Greek are
called 'other'--eteron). He who has both the two things in his mind,
cannot misplace them; and he who has only one of them in his mind,
cannot misplace them--on either supposition transplacement is
inconceivable.

But perhaps there may still be a sense in which we can think that
which we do not know to be that which we know: e.g. Theaetetus may know
Socrates, but at a distance he may mistake another person for him. This
process may be conceived by the help of an image. Let us suppose that
every man has in his mind a block of wax of various qualities, the gift
of Memory, the mother of the Muses; and on this he receives the seal or
stamp of those sensations and perceptions which he wishes to remember.
That which he succeeds in stamping is remembered and known by him as
long as the impression lasts; but that, of which the impression is
rubbed out or imperfectly made, is forgotten, and not known. No one can
think one thing to be another, when he has the memorial or seal of both
of these in his soul, and a sensible impression of neither; or when he
knows one and does not know the other, and has no memorial or seal of
the other; or when he knows neither; or when he perceives both, or one
and not the other, or neither; or when he perceives and knows both,
and identifies what he perceives with what he knows (this is still more
impossible); or when he does not know one, and does not know and does
not perceive the other; or does not perceive one, and does not know
and does not perceive the other; or has no perception or knowledge
of either--all these cases must be excluded. But he may err when he
confuses what he knows or perceives, or what he perceives and does not
know, with what he knows, or what he knows and perceives with what he
knows and perceives.

Theaetetus is unable to follow these distinctions; which Socrates
proceeds to illustrate by examples, first of all remarking, that
knowledge may exist without perception, and perception without
knowledge. I may know Theodorus and Theaetetus and not see them; I
may see them, and not know them. 'That I understand.' But I could not
mistake one for the other if I knew you both, and had no perception of
either; or if I knew one only, and perceived neither; or if I knew
and perceived neither, or in any other of the excluded cases. The only
possibility of error is: 1st, when knowing you and Theodorus, and having
the impression of both of you on the waxen block, I, s