Institutio Oratoria

There are also the following differences, that rhythm has unlimited space over which it may range, whereas the spaces of metre are confined, and that, whereas metre has certain definite cadences, rhythm may run on as it commenced until it reaches the point of μεταβολή, or transition to another type of rhythm: further, metre is concerned with words alone, while rhythm extends also to the motion of the body.

Again rhythm more readily admits of rests [*](i.e. in the musical sense. ) although they are found in metre as well. Greater license is, however, admitted when the time is measured by the beat of the feet or fingers, [*](i.e. in musio. ) and the intervals are distinguished by certain symbols indicating the number of shorts contained within a given space: hence we speak of four or five time ( τετράσημοι, or πεντάσημοι ) and others longer still, the Greek σημεῖον indicating a single beat.