The third element of rhythm that remains to be considered is tempo. And it is proposed to apply to this element also the same principles that have already been applied to time and metre. After what has been said, the matter will not be difficult.

Tempo presupposes a given time-system and a given metre. The tempo is slow when a time-unit, say a whole note, is held for a relatively long period, and all the other units take their proportional time. When a shorter time period is taken as a base, the tempo is faster. Often the tempo of a piece is left to the discretion of the performer. Sometimes, however, a composer wishes to indicate the exact speed with which he expects his music to be played; and he is enabled to do this accurately by indicating by the index number of a standard metronome what time should be allowed to a given unit. Thus, M. M. 60 indicates that the metronome beats sixty times to the minute, or one to the second; M. M. 100 represents a correspondingly higher speed, etc. Each one of such beats is the equivalent of a note of designated length, half, quarter, etc. The range of the accepted standard metronome is from 40 to 208 beats to the minute. It is understood, of course, that the use of the metronome suggested here is to set exact rates of speed, not that music should be practised to the accompaniment of a metronome.

In current musical practice the tempo of a given piece is the same for all the parts that are being played simultaneously, and it is likely to be the same, if not for the entire piece, at least for a passage of considerable length. If the tempo is changed within a given piece, there is no system determining the ratio between the consecutive tempi. Usually the relative speed of two portions is not evenly accurately designated, but merely indicated by the general captions, fast, slow; or allegro, adagio.