opinion consists in saying to yourself, that one thing is another. But did
you ever say to yourself, that good is evil, or evil good? Even in sleep,
did you ever imagine that odd was even? Or did any man in his senses ever
fancy that an ox was a horse, or that two are one? So that we can never
think one thing to be another; for you must not meet me with the verbal
quibble that one--eteron--is other--eteron (both 'one' and 'other' 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