SOCRATES: If a man has both of them in his thoughts, he cannot think that the one of them is the other?
THEAETETUS: True.
SOCRATES: Neither, if he has one of them only in his mind and not the other, can he think that one is the other?
THEAETETUS: True; for we should have to suppose that he apprehends that which is not in his thoughts at all.
SOCRATES: Then no one who has either both or only one of the two objects in his mind can think that the one is the other. And therefore, he who maintains that false opinion is heterodoxy is talking nonsense; for neither in this, any more than in the previous way, can false opinion exist in us.
THEAETETUS: No.
SOCRATES: But if, Theaetetus, this is not admitted, we shall be driven into many absurdities.
THEAETETUS: What are they?
SOCRATES: I will not tell you until I have endeavoured to consider the matter from every point of view. For I should be ashamed of us if we were driven in our perplexity to admit the absurd consequences of which I speak. But if we find the solution, and get away from them, we may regard them only as the difficulties of others, and the ridicule will not attach to us. On the other hand, if we utterly fail, I suppose that we must be humble, and allow the argument to trample us under foot, as the sea-sick passenger is trampled upon by the sailor, and to do anything to us. Listen, then, while I tell you how I hope to find a way out of our difficulty.
THEAETETUS: Let me hear.