Institutio Oratoria

Their first contention is based on the subject-matter; for they assert that all arts have their own subject-matter (which is true) and go on to say that rhetoric has none, which I shall show in what follows to be false.

Another slander is to the effect that no art will acquiesce in false opinions: since an art must be based on direct perception, which is always true: now, say they, rhetoric does give its assent to false conclusions and is therefore not an art.

I will admit that rhetoric sometimes substitutes falsehood for truth, but I will not allow that it does so because its opinions are false, since there is all the difference between holding a certain opinion oneself and persuading someone else to adopt an opinion. For instance a general frequently makes use of falsehood: Hannibal when hemmed in by Fabius persuaded his enemy that he was in retreat by