The Complete Aristotle (eng.)

the remark of
Xenophanes) the fair thing is for the impious man to offer the oath
and for the pious man to accept it; and that it would be monstrous
if you yourself were unwilling to accept an oath in a case where
you demand that the judges should do so before giving their
verdict. If you wish to offer an oath, you may argue that piety
disposes you to commit the issue to the gods; and that your
opponent ought not to want other judges than himself, since you
leave the decision with him; and that it is outrageous for your
opponents to refuse to swear about this question, when they insist
that others should do so.
    Now that we see how we are to argue in each case separately, we
see also how we are to argue when they occur in pairs, namely, when
you are willing to accept the oath but not to offer it; to offer it
but not to accept it; both to accept and to offer it; or to do
neither. These are of course combinations of the cases already
mentioned, and so your arguments also must be combinations of the
arguments already mentioned.
    If you have already sworn an oath that contradicts your present
one, you must argue that it is not perjury, since perjury is a
crime, and a crime must be a voluntary action, whereas actions due
to the force or fraud of others are involuntary. You must further
reason from this that perjury depends on the intention and not on
the spoken words. But if it is your opponent who has already sworn
an oath that contradicts his present one, you must say that if he
does not abide by his oaths he is the enemy of society, and that
this is the reason why men take an oath before administering the
laws. ‘My opponents insist that you, the judges, must abide by the
oath you have sworn, and yet they are not abiding by their own
oaths.’ And there are other arguments which may be used to magnify
the importance of the oath. [So much, then, for the ‘non-technical’
modes of persuasion.]

Rhetoric, Book II
    Translated by W. Rhys Roberts
<
    div id="book3" class="book">
    1
    We have now considered the materials to be used in supporting or
opposing a political measure, in pronouncing eulogies or censures,
and for prosecution and defence in the law courts. We have
considered the received opinions on which we may best base our
arguments so as to convince our hearers-those opinions with which
our enthymemes deal, and out of which they are built, in each of
the three kinds of oratory, according to what may be called the
special needs of each.
    But since rhetoric exists to affect the giving of decisions-the
hearers decide between one political speaker and another, and a
legal verdict is a decision-the orator must not only try to make
the argument of his speech demonstrative and worthy of belief; he
must also make his own character look right and put his hearers,
who are to decide, into the right frame of mind. Particularly in
political oratory, but also in lawsuits, it adds much to an
orator’s influence that his own character should look right and
that he should be thought to entertain the right feelings towards
his hearers; and also that his hearers themselves should be in just
the right frame of mind. That the orator’s own character should
look right is particularly important in political speaking: that
the audience should be in the right frame of mind, in lawsuits.
When people are feeling friendly and placable, they think one sort
of thing; when they are feeling angry or hostile, they think either
something totally different or the same thing with a different
intensity: when they feel friendly to the man who comes before them
for judgement, they regard him as having done little wrong, if any;
when they feel hostile, they take the opposite view. Again, if they
are eager for, and have good hopes of, a thing that will be
pleasant if it happens, they think that it certainly will happen
and be good for them: whereas if they are indifferent or annoyed,
they do not think so.
    There are three things which inspire confidence in the orator’s
own character-the three, namely, that induce us to believe a thing
apart from any proof of it: good sense, good moral character, and
goodwill. False statements and bad advice are due to one or more of
the following three causes. Men either form a false opinion through
want of good sense; or they form a true opinion, but because of
their moral badness do not say what they really think; or finally,
they are both sensible and upright, but not well disposed to their
hearers, and may fail