ere is difference
between the duty of this faculty and its end; that with respect to the
duty we consider what ought to be done; with respect to the end we
consider what is suitable to the duty. Just as we say, that it is the
duty of a physician to prescribe for a patient in a way calculated to
cure him; and that his end is to cure him by his prescriptions. And
so we shall understand what we are to call the duty of an orator, and
also what we are to call his end; since we shall call that his duty
which he ought to do, and we shall term that his end for the sake of
which he is bound to do his duty.

We shall call that the material of the art, on which the whole art,
and all that ability which is derived from art, turns. Just as if we
were to call diseases and wounds the material of medicine, because
it is about them that all medical science is concerned. And in like
manner, we call those subjects with which oratorical science and
ability is conversant the materials of the art of rhetoric. And these
subjects some have considered more numerous, and others less so. For
Gorgias the Leontine, who is almost the oldest of all rhetoricians,
considered that an orator was able to speak in the most excellent
manner of all men on every subject. And when he says this he seems to
be supplying an infinite and boundless stock of materials to this art.
But Aristotle, who of all men has supplied the greatest number of aids
and ornaments to this art, thought that the duty of the rhetorician
was conversant with three kinds of subjects; with the demonstrative,
and the deliberative, and the judicial.

The demonstrative is that which concerns itself with the praise or
blame of some particular individual; the deliberative is that which,
having its place in discussion and in political debate, comprises a
deliberate statement of one's opinion; the judicial is that which,
having its place in judicial proceedings, comprehends the topics of
accusation and defence; or of demand and refusal. And, as our own
opinion at least inclines, the art and ability of the orator must be
understood to be conversant with these tripartite materials. VI For
Hermagoras, indeed, appears neither to attend to what he is saying,
nor to understand what he is promising, for he divides the materials
of an orator into the cause, and the examination. The cause he defines
to be a thing which has in itself a controversy of language united
with the interposition of certain char