As, for example, in the case of the sun, I think that you
would be contented with the statement that the sun is the brightest of
the heavenly bodies which revolve about the earth.

THEAETETUS: Certainly.

SOCRATES: Understand why:--the reason is, as I was just now saying, that
if you get at the difference and distinguishing characteristic of each
thing, then, as many persons affirm, you will get at the definition or
explanation of it; but while you lay hold only of the common and not of
the characteristic notion, you will only have the definition of those
things to which this common quality belongs.

THEAETETUS: I understand you, and your account of definition is in my
judgment correct.

SOCRATES: But he, who having right opinion about anything, can find out
the difference which distinguishes it from other things will know that
of which before he had only an opinion.

THEAETETUS: Yes; that is what we are maintaining.

SOCRATES: Nevertheless, Theaetetus, on a nearer view, I find myself
quite disappointed; the picture, which at a distance was not so bad, has
now become altogether unintelligible.

THEAETETUS: What do you mean?

SOCRATES: I will endeavour to explain: I will suppose myself to have
true opinion of you, and if to this I add your definition, then I have
knowledge, but if not, opinion only.

THEAETETUS: Yes.

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.

SOCRATES: Surely I can have no conception of Theaetetus until your
snub-nosedness has left an impression on my mind different from the
snub-nosedne