Institutio Oratoria

But these arguments may readily be met by arguments from dissimilars:

It is not the same thing for the master of the house to have intercourse with a female slave as for the mistress to have intercourse with a male slave; nor does it follow that because dumb animals pursue pleasure, reasoning beings should do likewise.

Because pleasure is an end sought by dumb animals, it should not be sought by reasoning beings.

Authority also may be drawn from external sources to support a case. Those who follow the Greeks, who call such arguments κρίσεις, style them judgments or adjudications, thereby referring not to matters on which judicial sentence has been pronounced (for such decisions form examples or precedents), but to whatever may be regarded as expressing the opinion of nations, peoples, philosophers, distinguished citizens, or illustrious poets. Nay,

even common sayings and popular beliefs may be found to be useful. For they form a sort of testimony, which is rendered all the more impressive by the fact that it was not given to suit special cases, but was the utterance or action of minds swayed neither by prejudice or influence, simply because it seemed the most honourable or honest thing to say or do.