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. Book I deals with the speaker as himself the prime means of persuasion. Rhetoric, Aristotle implies, is necessarily ethical in that everything consecutively imparted or communicated, as distinct from the abstractions of geometry or logic, is subjective. Moreover, in making the speaker the point of departure Aristotle admits that other trend of classical pedagogy which made rhetoric a cultivation of personality. Book II, proceeding to the second item of the division above, deals with the audience, with knowledge of human nature, especially of typical habits of mind; for rhetoric in this aspect too is ethical. It deals with the interaction of moral forces in speaker and audience, and also with the direct arousing of emotion. The speech itself, the final utterance, which is the subject of Book III, has thus been approached as the art of adjusting the subject-matter of a given case through the intelligence and emotion of the speaker to the intelligence and emotion of the audience. This is the only book of very specific technic; and it comes last psychologically.