The Complete Aristotle (eng.)

into examples, in order to
show what is not yet known, that Dionysius has the same purpose in
making the same request: all these being instances of the one
general principle, that a man who asks for a bodyguard is scheming
to make himself a despot. We have now described the sources of
those means of persuasion which are popularly supposed to be
demonstrative.
    There is an important distinction between two sorts of
enthymemes that has been wholly overlooked by almost everybody-one
that also subsists between the syllogisms treated of in dialectic.
One sort of enthymeme really belongs to rhetoric, as one sort of
syllogism really belongs to dialectic; but the other sort really
belongs to other arts and faculties, whether to those we already
exercise or to those we have not yet acquired. Missing this
distinction, people fail to notice that the more correctly they
handle their particular subject the further they are getting away
from pure rhetoric or dialectic. This statement will be clearer if
expressed more fully. I mean that the proper subjects of
dialectical and rhetorical syllogisms are the things with which we
say the regular or universal Lines of Argument are concerned, that
is to say those lines of argument that apply equally to questions
of right conduct, natural science, politics, and many other things
that have nothing to do with one another. Take, for instance, the
line of argument concerned with ‘the more or less’. On this line of
argument it is equally easy to base a syllogism or enthymeme about
any of what nevertheless are essentially disconnected
subjects-right conduct, natural science, or anything else whatever.
But there are also those special Lines of Argument which are based
on such propositions as apply only to particular groups or classes
of things. Thus there are propositions about natural science on
which it is impossible to base any enthymeme or syllogism about
ethics, and other propositions about ethics on which nothing can be
based about natural science. The same principle applies throughout.
The general Lines of Argument have no special subject-matter, and
therefore will not increase our understanding of any particular
class of things. On the other hand, the better the selection one
makes of propositions suitable for special Lines of Argument, the
nearer one comes, unconsciously, to setting up a science that is
distinct from dialectic and rhetoric. One may succeed in stating
the required principles, but one’s science will be no longer
dialectic or rhetoric, but the science to which the principles thus
discovered belong. Most enthymemes are in fact based upon these
particular or special Lines of Argument; comparatively few on the
common or general kind. As in the therefore, so in this work, we
must distinguish, in dealing with enthymemes, the special and the
general Lines of Argument on which they are to be founded. By
special Lines of Argument I mean the propositions peculiar to each
several class of things, by general those common to all classes
alike. We may begin with the special Lines of Argument. But, first
of all, let us classify rhetoric into its varieties. Having
distinguished these we may deal with them one by one, and try to
discover the elements of which each is composed, and the
propositions each must employ.
3
    Rhetoric falls into three divisions, determined by the three
classes of listeners to speeches. For of the three elements in
speech-making—speaker, subject, and person addressed—it is the last
one, the hearer, that determines the speech’s end and object. The
hearer must be either a judge, with a decision to make about things
past or future, or an observer. A member of the assembly decides
about future events, a juryman about past events: while those who
merely decide on the orator’s skill are observers. From this it
follows that there are three divisions of oratory-(1) political,
(2) forensic, and (3) the ceremonial oratory of display.
    Political speaking urges us either to do or not to do something:
one of these two courses is always taken by private counsellors, as
well as by men who address public assemblies. Forensic speaking
either attacks or defends somebody: one or other of these two
things must always be done by the parties in a case. The ceremonial
oratory of display either praises or censures somebody. These three
kinds of rhetoric refer to three different kinds of time. The
political orator is concerned with the future: it is about things
to be done