The Complete Aristotle (eng.)

dialectic is the scientific
study of any one separate subject: both are faculties for providing
arguments. This is perhaps a sufficient account of their scope and
of how they are related to each other.
    With regard to the persuasion achieved by proof or apparent
proof: just as in dialectic there is induction on the one hand and
syllogism or apparent syllogism on the other, so it is in rhetoric.
The example is an induction, the enthymeme is a syllogism, and the
apparent enthymeme is an apparent syllogism. I call the enthymeme a
rhetorical syllogism, and the example a rhetorical induction. Every
one who effects persuasion through proof does in fact use either
enthymemes or examples: there is no other way. And since every one
who proves anything at all is bound to use either syllogisms or
inductions (and this is clear to us from the Analytics), it must
follow that enthymemes are syllogisms and examples are inductions.
The difference between example and enthymeme is made plain by the
passages in the Topics where induction and syllogism have already
been discussed. When we base the proof of a proposition on a number
of similar cases, this is induction in dialectic, example in
rhetoric; when it is shown that, certain propositions being true, a
further and quite distinct proposition must also be true in
consequence, whether invariably or usually, this is called
syllogism in dialectic, enthymeme in rhetoric. It is plain also
that each of these types of oratory has its advantages. Types of
oratory, I say: for what has been said in the Methodics applies
equally well here; in some oratorical styles examples prevail, in
others enthymemes; and in like manner, some orators are better at
the former and some at the latter. Speeches that rely on examples
are as persuasive as the other kind, but those which rely on
enthymemes excite the louder applause. The sources of examples and
enthymemes, and their proper uses, we will discuss later. Our next
step is to define the processes themselves more clearly.
    A statement is persuasive and credible either because it is
directly self-evident or because it appears to be proved from other
statements that are so. In either case it is persuasive because
there is somebody whom it persuades. But none of the arts theorize
about individual cases. Medicine, for instance, does not theorize
about what will help to cure Socrates or Callias, but only about
what will help to cure any or all of a given class of patients:
this alone is business: individual cases are so infinitely various
that no systematic knowledge of them is possible. In the same way
the theory of rhetoric is concerned not with what seems probable to
a given individual like Socrates or Hippias, but with what seems
probable to men of a given type; and this is true of dialectic
also. Dialectic does not construct its syllogisms out of any
haphazard materials, such as the fancies of crazy people, but out
of materials that call for discussion; and rhetoric, too, draws
upon the regular subjects of debate. The duty of rhetoric is to
deal with such matters as we deliberate upon without arts or
systems to guide us, in the hearing of persons who cannot take in
at a glance a complicated argument, or follow a long chain of
reasoning. The subjects of our deliberation are such as seem to
present us with alternative possibilities: about things that could
not have been, and cannot now or in the future be, other than they
are, nobody who takes them to be of this nature wastes his time in
deliberation.
    It is possible to form syllogisms and draw conclusions from the
results of previous syllogisms; or, on the other hand, from
premisses which have not been thus proved, and at the same time are
so little accepted that they call for proof. Reasonings of the
former kind will necessarily be hard to follow owing to their
length, for we assume an audience of untrained thinkers; those of
the latter kind will fail to win assent, because they are based on
premisses that are not generally admitted or believed.
    The enthymeme and the example must, then, deal with what is in
the main contingent, the example being an induction, and the
enthymeme a syllogism, about such matters. The enthymeme must
consist of few propositions, fewer often than those which make up
the normal syllogism. For if any of these propositions is a
familiar fact, there is no need even to mention it; the hearer adds
it himself. Thus, to show that Dorieus has been victor in a contest
for which the