Institutio Oratoria

For whatever we say that falls outside the five divisions of the speech already laid down is a digression, whether it express indignation, pity, hatred, rebuke, excuse, conciliation or be designed to rebut invective. Other similar occasions for digression on points not involved by the question at issue arise when we amplify or abridge a topic, make any kind of emotional appeal or introduce any of those topics which add such charm and elegance to oratory, topics that is to say such as luxury, avarice, religion, duty: but these would hardly seem to be digressions as they are so closely attached to arguments on similar subjects that they form part of the texture of the speech.