Book 2
23.1
One topic of demonstrative enthymemes is derived from opposites; for it is necessary to consider whether one opposite is predicable of the other, as a means of destroying an argument, if it is not, as a means of constructing one, if it is;Assuming that self-control is good, then if the opposite of good (that is, bad) can be predicated of lack of self-control, this proves the truth of the first proposition; otherwise, it may be refuted. for instance, self-control is good, for lack of self-control is harmful; or as in the Messeniacus,Cf. 1.13.2 note. If the war is responsible for the present evils, one must repair them with the aid of peace. And, For if it is unfair to be angry with those who have done wrong unintentionally, it is not fitting to feel beholden to one who is forced to do us good.Authorship unknown. Or, If men are in the habit of gaining credit for false statements, you must also admit the contrary, that men often disbelieve what is true.Euripides, Thyestes (Frag. 396, T.G.F.).
23.2
Another topic is derived from similar inflections, for in like manner the derivatives must either be predicable of the subject or not; for instance, that the just is not entirely good, for in that case good would be predicable of anything that happens justly; but to be justly put to death is not desirable.
