The four motions
Between two voices: parallel (same interval, same direction), similar (same direction, different interval), contrary (opposite directions), oblique (one voice stays, the other moves). Contrary motion is the most independent; parallel the least.
The classical rules
- No parallel fifths and octaves (nor parallel unisons) between any two voices: two voices moving together in fifths or octaves lose independence.
- No hidden fifths/octaves between the outer voices when the soprano arrives by leap.
- Leading tone (B in C) rising to the tonic when it is in an outer voice.
- Seventh of the chord (F in G7) falling by step.
- Common tones held in the same voice; the other voices move by the shortest route.
- No augmented melodic intervals (F–G# in harmonic A minor) and no leaps of a seventh.
- Spacing: soprano–alto and alto–tenor within an octave; tenor–bass may be wider.
- No voice crossing (the alto above the soprano) or overlapping.
Examples in C
- C → F: C E G → C F A (C stays, E rises to F, G rises to A).
- G7 → C: B rises to C, F falls to E, D goes to C (or to E), the bass G goes to C.
- Typical mistake: C (C E G) → D (D F# A) with all voices rising by a whole step: parallel fifths and octaves.
Why it matters to a producer
The same rules make pad, string, choir and piano voicings smooth. A C – G – Am – F loop played as root-position blocks jumps up and down; with voice leading: C E G → B D G → C E A → C F A, the hand barely moves and the inner voices sing.
Real example
The 371 chorales harmonized by Bach have been the reference model for these rules for three centuries; ABRSM Grade 6 programs ask precisely for completing phrases in chorale style.