The Complete Aristotle (eng.)

are what the
supporter of a measure maintains they are. In forensic oratory this
is not enough; to conciliate the listener is what pays here. It is
other people’s affairs that are to be decided, so that the judges,
intent on their own satisfaction and listening with partiality,
surrender themselves to the disputants instead of judging between
them. Hence in many places, as we have said already, irrelevant
speaking is forbidden in the law-courts: in the public assembly
those who have to form a judgement are themselves well able to
guard against that.
    It is clear, then, that rhetorical study, in its strict sense,
is concerned with the modes of persuasion. Persuasion is clearly a
sort of demonstration, since we are most fully persuaded when we
consider a thing to have been demonstrated. The orator’s
demonstration is an enthymeme, and this is, in general, the most
effective of the modes of persuasion. The enthymeme is a sort of
syllogism, and the consideration of syllogisms of all kinds,
without distinction, is the business of dialectic, either of
dialectic as a whole or of one of its branches. It follows plainly,
therefore, that he who is best able to see how and from what
elements a syllogism is produced will also be best skilled in the
enthymeme, when he has further learnt what its subject-matter is
and in what respects it differs from the syllogism of strict logic.
The true and the approximately true are apprehended by the same
faculty; it may also be noted that men have a sufficient natural
instinct for what is true, and usually do arrive at the truth.
Hence the man who makes a good guess at truth is likely to make a
good guess at probabilities.
    It has now been shown that the ordinary writers on rhetoric
treat of non-essentials; it has also been shown why they have
inclined more towards the forensic branch of oratory.
    Rhetoric is useful (1) because things that are true and things
that are just have a natural tendency to prevail over their
opposites, so that if the decisions of judges are not what they
ought to be, the defeat must be due to the speakers themselves, and
they must be blamed accordingly. Moreover, (2) before some
audiences not even the possession of the exactest knowledge will
make it easy for what we say to produce conviction. For argument
based on knowledge implies instruction, and there are people whom
one cannot instruct. Here, then, we must use, as our modes of
persuasion and argument, notions possessed by everybody, as we
observed in the Topics when dealing with the way to handle a
popular audience. Further, (3) we must be able to employ
persuasion, just as strict reasoning can be employed, on opposite
sides of a question, not in order that we may in practice employ it
in both ways (for we must not make people believe what is wrong),
but in order that we may see clearly what the facts are, and that,
if another man argues unfairly, we on our part may be able to
confute him. No other of the arts draws opposite conclusions:
dialectic and rhetoric alone do this. Both these arts draw opposite
conclusions impartially. Nevertheless, the underlying facts do not
lend themselves equally well to the contrary views. No; things that
are true and things that are better are, by their nature,
practically always easier to prove and easier to believe in. Again,
(4) it is absurd to hold that a man ought to be ashamed of being
unable to defend himself with his limbs, but not of being unable to
defend himself with speech and reason, when the use of rational
speech is more distinctive of a human being than the use of his
limbs. And if it be objected that one who uses such power of speech
unjustly might do great harm, that is a charge which may be made in
common against all good things except virtue, and above all against
the things that are most useful, as strength, health, wealth,
generalship. A man can confer the greatest of benefits by a right
use of these, and inflict the greatest of injuries by using them
wrongly.
    It is clear, then, that rhetoric is not bound up with a single
definite class of subjects, but is as universal as dialectic; it is
clear, also, that it is useful. It is clear, further, that its
function is not simply to succeed in persuading, but rather to
discover the means of coming as near such success as the
circumstances of each particular case allow. In this it resembles
all other arts. For example, it is not the function of medicine
simply to make a man quite healthy, but to put him as far