and we were to reply, that there is a clay of potters, there is a clay
of oven-makers, there is a clay of brick-makers; would not the
answer be ridiculous?

  Theaet. Truly.

  Soc. In the first place, there would be an absurdity in assuming
that he who asked the question would understand from our answer the
nature of "clay," merely because we added "of the image-makers," or of
any other workers. How can a man understand the name of anything, when
he does not know the nature of it?

  Theaet. He cannot.

  Soc. Then he who does not know what science or knowledge is, has
no knowledge of the art or science of making shoes?

  Theaet. None.

  Soc. Nor of any other science?

  Theaet. No.

  Soc. And when a man is asked what science or knowledge is, to give
in answer the name of some art or science is ridiculous; for the
-question is, "What is knowledge?" and he replies, "A knowledge of
this or that."

  Theaet. True.

  Soc. Moreover, he might answer shortly and simply, but he makes an
enormous circuit. For example, when asked about the day, he might have
said simply, that clay is moistened earth-what sort of clay is not
to the point.

  Theaet. Yes, Socrates, there is no difficulty as you put the
question. You mean, if I am not mistaken, something like what occurred
to me and to my friend here, your namesake Socrates, in a recent
discussion.

  Soc. What was that, Theaetetus?

  Theaet. Theodorus was writing out for us something about roots, such
as the roots of three or five, showing that they are incommensurable
by the unit: he selected other examples up to seventeen-there he
stopped. Now as there are innumerable roots, the notion occurred to us
of attempting to include them all under one name or class.

  Soc. And did you find such a class?