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 if it makes no difference whether the final syllable be long or short, the concluding feet in these two instances must be identical: and yet somehow or other one gives the impression of sitting down and the other of a simple halt. This fact has led some critics to allow three timebeats for a final long syllable, adding the extra
It is not, however, necessary to go back further than three feet, and only that if the feet contain less than three syllables, for we must avoid the exactitude of verse: on the other hand, we must not go back less than two: otherwise we shall be dealing with a foot and not with rhythm. But in this connexion the dichoreus may be regarded as one foot, if indeed a foot consisting of two chorei can be considered as a single foot.