The real innovation in "Similar Motion" is its sense of drama. The earlier pieces were meditative, steady-state pieces that established a mood and stayed there. But "Similar Motion" starts with one voice, then adds another playing a fourth above the original line, and then another playing a fourth below the original line, and finally a bass line kicks in to complete the sound. As each new voice enters, there is a dramatic change in the music.
© Philip Glass
Each figure should be repeated an indefinite number of times. The leader of the ensemble should, at his or her discretion, nod once, indicating that the ensemble should repeat the figure twice more before proceeding. Exceptions to this are indicated, and last until the next indication.
It is possible for the piece to be played through without any optional repeats to last for about 6 minutes. On the other hand, in theory, the leader of the ensemble could indicate sufficient repeats by the nod of a head that the work would last all night – even eternally. But based upon the composer’s own practice in performance, there is a suggested duration for the work of anywhere between 17 and 25 minutes.
The piece should be played at a constant dynamic: forte.
Players must choose what direction to take where the third and fourth voices enter: either everybody is playing constantly and either they divide there or they enter the work at that point. Keyboard players will play from two staves.