Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
Thus the works of the orator will be great not extravagant, sublime not bombastic, bold not rash, severe but not gloomy, grave but not slow, rich but not luxuriant, pleasing but not effeminate, grand but not grandiose. It is the same with other qualities: the mean is safest, for the worst of all faults is to fly to extremes.