Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
For the writers of text-books do not forbid it because they regard it as illicit, but because they think it useless. Consequently if its utility be proved, we shall have to employ it for the very reason for which we are now forbidden to do so.
Moreover Demosthenes
v4-6 p.43
turns to address Aeschines in his exordium, [*](de Cor.) while Cicero adopts the same device in several of his speeches, but more especially in the pro Ligario, [*](i. 2.) where he turns to address Tubero. His speech would have been much less effective, if any other figure had been used, as will be all the more clearly realised, if the whole of that most vigorous passage
You are, then, in possession, Tubero, of the most valuable advantage that can fall to an accuser etc.be altered so as to be addressed to the judge. For it is a real and most unnatural diversion of the passage, which destroys its whole force, if we say
Tubero is then in possession of the most valuable advantage that can fall to an accuser.