Parallel motion means that two voices move in the same direction, thereby preserving the same generic vertical interval between them. Both voices can move stepwise or by leap. The direction of both voices can change with every note or remain the same for several notes. In what is today generically called ‘tonal’ music (in itself a problematic term), the vertical intervals that can usually occur in succession are thirds and sixths (the imperfect consonances). Parallel motion tends not to last too long in contrapuntal settings, since it compromises the independence of the voices. The example below is thus more a demonstration of parallel motion than a voice leading that might occur in actual music.
Parallel motion can also occur when a 4–3 appoggiatura resolves not over the same bass note but over the bass note one step lower, resulting in parallel vertical fourths. In the second half of the first bar of the example below, both vertical fourths are perfect; in the first half of the third bar, the first is perfect and the second augmented.
A three-part example of parallel motion is fauxbourdon.
In ‘tonal’ music, parallel fifths and octaves are generally prohibited, whereas in other styles of music they do occur.
When, however, the generic vertical interval between the two voices changes, we speak of similar motion.
Other contrapuntal motions are:
- Contrary motion
- Oblique motion