Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
while the figures must neither be derived from poetry nor such as are contrary to current usage, though warranted by the authority of antiquity (for it is important that our language should be entirely normal), but should be designed to relieve tedium by their variety and should be frequently
Moreover there is no portion of a speech at which the judge is more attentive, and consequently nothing that is well said is lost. And the judge is, for some reason or other, all the more ready to accept what charms his ear and is lured by pleasure to belief.