Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
Generally received sayings also become common property owing to the very fact that they are anonymous, as, for instance,
Friends are a treasure,or
Conscience is as good as a thousand witnesses,or, to quote Cicero, [*](Cato maj. iii 7. )
In the words of the old proverb, birds of a feather flock together.Sayings such as these would not have acquired immortality had they not carried conviction of their truth to all mankind.
Some include under this head the supernatural authority that is derived from oracles, as for instance the response asserting that Socrates was the wisest of mankind: indeed, they
Sometimes, again, it may be possible to produce some saying or action of the judge, of our adversary or his advocate in order to prove our point. There have therefore been some writers who have regarded examples and the use of authorities of which I am speaking as belonging to inartificial proofs, on the ground that the orator does not discover them, but receives them readymade. But the point is of great importance.
For witnesses and investigation and the like all make some pronouncement on the actual matter under trial, whereas arguments drawn from without are in themselves useless, unless the pleader has the wit to apply them in such a manner as to support the points which he is trying to make.