SOCRATES: The definition was assumed to be the interpretation of your difference.
THEAETETUS: True.
SOCRATES: But when I had only opinion, I had no conception of your distinguishing characteristics.
THEAETETUS: I suppose not.
SOCRATES: Then I must have conceived of some general or common nature which no more belonged to you than to another.
THEAETETUS: True.
SOCRATES: Tell me, now—How in that case could I have formed a judgment of you any more than of any one else? Suppose that I imagine Theaetetus to be a man who has nose, eyes, and mouth, and every other member complete; how would that enable me to distinguish Theaetetus from Theodorus, or from some outer barbarian?
THEAETETUS: How could it?
SOCRATES: Or if I had further conceived of you, not only as having nose and eyes, but as having a snub nose and prominent eyes, should I have any more notion of you than of myself and others who resemble me?
THEAETETUS: Certainly not.