Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
The definition which best suits its real character is that which makes rhetoric the science of speaking well. For this definition includes all the virtues of oratory and the character of the orator as well, since no man can speak well who is not good himself.
The definition given by Chrysippus, who
Areus again defines it well as speaking according to the excellence of speech. Those who regard it as the science of political obligations, also exclude men of bad character from the title of orator, if by science they mean virtue, but restrict it overmuch by confining it to political problems. Albutius, a distinguished author and professor of rhetoric, agrees that rhetoric is the science of speaking well, but makes a mistake in imposing restrictions by the addition of the words on political questions and with credibility; with both of these restrictions I have already dealt.