Chapter II: , may be summed up in the word persuasion, if we are careful

to speak of persuasion not as achievement, but as method. Just as we ask of medicine, not that it shall infallibly heal—a degree of achievement impossible in human affairs—but that it shall discern and use all the means of healing available in the given case, so the true end of rhetoric is to induce such habitual skill as shall _discern in any given case the available means of persuasion_.[6]

As means of persuasion we must include both those that are extrinsic and those that are intrinsic,[7] those that lie outside the art of rhetoric in the domains of subject-matter and those that lie within, the facts of the case and the technic of making them tell. For rhetoric has to include subject-matter, the forces of knowledge. Though this is extrinsic in the sense of lying outside the art of rhetoric, it is essential. Rhetoric is an art, as Aristotle is careful to show; but it differs from other arts in the degree of importance it must always attach to its subject-matter. The division here into extrinsic means and intrinsic means as both necessary to persuasion is not merely the obvious one into matter and manner, substance and style; it is a division of the springs of composition, the sources of effectiveness, into those that lie outside and those that lie inside of utterance, or presentation. It frankly accepts rhetoric as more than artistic, as never self-sufficient and absolute, as always relating presentation to investigation.

Equally philosophical is the following division[8] of the intrinsic means of persuasion into: (1) those inherent in the character or moral potentiality (ἦθος) of the speaker, (2) those inherent in his actual moving of the audience, and (3) those inherent in the form and phrase of the speech itself. That the three are not mutually exclusive is evident and must have been deliberate. Aristotle is telling us that rhetoric as an art is to be approached from these three directions and in this order. The division is comprehensive not only as being satisfying psychologically, but as constituting an outline for the whole work, the headings of the development in three books: first, the speaker himself; secondly, the audience; and finally, in the light of these two, and as the bringing of the one to bear on the other, the speech.