Institutio Oratoria

Quintilian

Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.

But we may also borrow from a word of cognate meaning. For

I understand,
or
I feel
or
I see
are often equivalent to
I know.
Reading will provide us with a rich store of expressions such as these, and will enable us not merely to use them when they occur to us, but also in the appropriate manner. For they are not always interchangeable:

for example, though I may be perfectly correct in saying,

I see
for
I understand,
it does not follow that I can say
I understand
for
my eyes have seen,
and though mucro may be employed to describe a sword, a sword does not necessarily mean the same as mucro (point).

But, although a store of words may be acquired by these means, we must not read or listen to orators merely for the sake of acquiring words. For in everything which we teach examples are more effective even than the rules which are taught in the schools, so long as the student has reached a stage when he can appreciate such examples without the assistance of a teacher, and can rely on his own powers to imitate them. And the reason is this, that the professor of rhetoric lays down rules, while the orator gives a practical demonstration.