Then this is the goal of all his effort; he tries to produce conviction in the soul. Is not that so?
Yes.
So it is clear that Thrasymachus, or anyone else who seriously teaches the art of rhetoric, will first describe the soul with perfect accuracy and make us see whether it is one and all alike, or, like the body, of multiform aspect; for this is what we call explaining its nature.
Certainly.
And secondly he will say what its action is and toward what it is directed, or how it is acted upon and by what.
To be sure.
Thirdly, he will classify the speeches and the souls and will adapt each to the other, showing the causes of the effects produced and why one kind of soul is necessarily persuaded by certain classes of speeches, and another is not.
That would, I think, be excellent.
By no other method of exposition or speech will this, or anything else, ever be written
or spoken with real art. But those whom you have heard, who write treatises on the art of speech nowadays, are deceivers and conceal the nature of the soul, though they know it very well. Until they write and speak by this method we cannot believe that they write by the rules of art.
What is this method?
It is not easy to tell the exact expressions to be used; but I will tell how one must write, if one is to do it, so far as possible, in a truly artistic way.
Speak then.
Since it is the function of speech
to lead souls by persuasion, he who is to be a rhetorician must know the various forms of soul. Now they are so and so many and of such and such kinds, wherefore men also are of different kinds: these we must classify. Then there are also various classes of speeches, to one of which every speech belongs. So men of a certain sort are easily persuaded by speeches of a certain sort for a certain reason to actions or beliefs of a certain sort, and men of another sort cannot be so persuaded. The student of rhetoric must, accordingly, acquire a proper knowledge of these classes and then be able to follow them
accurately with his senses when he sees them in the practical affairs of life; otherwise he can never have any profit from the lectures he may have heard.