The next thing is the principle of arguing, and the knowledge of nature. For we will examine the chief good presently, as I said before, and apply the whole discussion to the explanation of it. There was, then, in those two parts nothing which Zeno wished to alter. For the whole thing, in both its divisions, is in an excellent state; for what has been omitted by the ancients in that kind of argument which is of influence in discussion? For they have both given many definitions, and have bequeathed to us titles for defining; and that important addition to definition, I mean the dividing of the subject into parts, is both done by them, and they have also left us rules to enable us to do so too; and I may say the same of contraries; from which they came to genera, and to the forms of genera. Now, they make those things which they call evident, the beginning of an argument concluded by reason: then they follow an orderly arrangement; and the conclusion at last shows what is true in the separate propositions. But what a great variety of arguments, which lead to conclusions according to reason, do they give us, and how dissimilar are they to captious questions! What shall we say of their denouncing, as it were, in many places, that we ought neither entirely to trust our senses when unsupported by reason, nor reason when unsupported by our senses; but that, at the same time, we ought to keep the line betweenthe two clearly marked? What shall I say more? Were not all the precepts which the dialecticians now deliver and teach, originally discovered and established by them? And although they were very much elaborated by Chrysippus, still they were much less practised by Zeno than by the ancients. And there were several things in which he did not improve on the ancients; and some which he never touched at all. And as there are two arts by which reason and oratory are brought to complete perfection, one that of discovering, the other that of arguing,—both the Stoics and Peripatetics have handed us down this latter, but the Peripatetics alone have given us rules for the former, while the Stoics have altogether avoided it. For the men of your school never even suspected the places from which arguments might be drawn as out of magazines; but the Peripatetics taught a regular system and method.
And the consequence is, that it is not necessary for one now to be always repeating a sort of dictated lesson on the same subject, or to be afraid to go beyond one's note-books: for he who knows where everything is placed, and how he can arrive at it, even if anything be completely buried, will be able to dig it up, and will always have his wits about him in every discussion. And although men who are endowed with great abilities, attain to a certain copiousness of eloquence without any definite principles of oratory, still art is a surer guide than nature. For it is one thing to pour out words after the fashion of poets, and another to distinguish on settled principles and rules all that you say.