THEAETETUS: How?

STRANGER: There is one part which is distinguished as the sale of a

man's own productions; another, which is the exchange of the works of

others.

THEAETETUS: Certainly.

STRANGER: And is not that part of exchange which takes place in the

city, being about half of the whole, termed retailing?

THEAETETUS: Yes.

STRANGER: And that which exchanges the goods of one city for those of

another by selling and buying is the exchange of the merchant?

THEAETETUS: To be sure.

STRANGER: And you are aware that this exchange of the merchant is of

two kinds: it is partly concerned with food for the use of the body,

and partly with the food of the soul which is bartered and received in

exchange for money.

THEAETETUS: What do you mean?

Sophist