Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
Aristotle seems to have implied that the sphere of the orator was all-inclusive when he defined rhetoric as the power to detect every element in any given subject which might conduce to persuasion; so too does Patrocles who omits the words in any given subject, but since he excludes nothing, shows that his view is identical. For he defines rhetoric as the power to discover whatever is persuasive in speech. These definitions like that quoted above include no more than the power of invention alone. Theodorus avoids this fault and holds that it is the power to discover and to utter forth in elegant language whatever is credible in every subject of oratory.
But, while others besides
. Plato makes Gorgias [*](Gorg. 454 B. ) say that he is a master of persuasion in the law-courts and other assemblies, and that his themes are justice and injustice, while in reply Socrates allows him the power of persuading, but not of teaching.