Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
However, I pass this by; for I am sure that no one with the least smattering of literary culture will have the slightest hesitation in agreeing with me. I will proceed to my next point, that no one will achieve sufficient skill even in speaking, unless he makes a thorough study of all the workings of nature and forms his character on the precepts of philosophy and the dictates of reason.
For it is with good cause that Lucius Crassus, in the
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third book of the de Oratore, [*](Chs. xx. xxvii. and xxxi.) affirms that all that is said concerning equity, justice, truth and the good, and their opposites, forms part of the studies of an orator, and that the philosophers, when they exert their powers of speaking to defend these virtues, are using the weapons of rhetoric, not their own. But he also confesses that the knowledge of these subjects must be sought from the philosophers for the reason that, in his opinion, philosophy has more effective possession of them.