Parallel octaves · Rules
Two voices an octave or a unison apart do not move to another octave or unison in the next chord, whether by similar or contrary motion, nor as compound intervals (fifteenth): the two voices would lose their independence.
- Parallel octaves: Two voices an octave or a unison apart do not move to another octave or unison in the next chord, whether by similar or contrary motion, nor as compound intervals (fifteenth): the two voices would lose their independence. (Piston, ch. 3, pp. 29–30 and 34)