Institutio Oratoria

All combination, arrangement and connexion of words involves either rhythms (which we call numeri ), or metres, that is, a certain measure. Now though both rhythm and metre consist of feet, they differ in more than one respect.

For in the first place rhythm consists of certain lengths of time, while metre is determined by the order in which these lengths are arranged. Consequently the one seems to be concerned with quantity and the other with quality. Rhythm may depend on equal balance,

as in the case of dactylic rhythm, where one long syllable balances two short, (there are it is true other feet of which this statement is equally true, but the title of dactylic has been currently applied to all, [*]( For purely rhythmical purposes the term dactyl is arbitrarily used by the rhetoricians to include anapaests as well. See below. ) while even boys are well aware that a long syllable is equivalent to two beats and a short to one) or it may consist of feet in which one portion is half as long again as the other, as is the case with paeanic rhythm (a paean being composed of one long followed by three shorts, three shorts followed by one long or with any other arrangement preserving the proportion of three beats to two) or finally one part of the foot may be twice the length of the other, as in the case of the iambus, which is composed of a short followed by a long, or of the choreus consisting of a long followed by a short.