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 objection to this practice lies in the fact that they do this without the slightest consideration of the difference between case and case or reflecting whether what they are doing will in any way assist them, on the assumption that it is always expedient and always necessary. Consequently they transfer striking thoughts from the places which they should have occupied elsewhere and concentrate them in this portion of the speech, a practice which involves either the repetition of a number of things that they have already said or their omission from the place which was really theirs owing to the fact that they have already been said.
I admit however that this form of digression can be advantageously appended, not merely to the statement of facts, but to each of the different questions or to the questions as a whole,