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Voice leading refers to the horizontal motion of individual voices as harmony changes. The central principle is smoothness: voices should move by step when possible and avoid large leaps, preserving the independence and singability of each line. The two most important prohibitions in tonal voice leading are parallel perfect fifths and parallel perfect octaves — when two voices move in the same direction to the same interval class, their independence collapses. Contrary motion (voices moving in opposite directions) is the strongest tool for maintaining independence, while oblique and similar motion provide variety.
Work through pairs of chords mapping each voice's motion before writing anything. Use the 'sing-ability test': can a choral singer comfortably sing your line? Study Bach four-part chorales, tracking the motion of each voice pair and noting how parallel fifths and octaves are systematically avoided.
Voice leading is the study of how individual voices — soprano, alto, tenor, bass — move horizontally as chords change. From your study of intervals, you know that a perfect fifth sounds open and stable, and a unison or octave sounds completely fused. These perceptual properties are exactly why voice leading has rules: harmony works when individual lines sound like independent voices with their own melodic identities, rather than a single blob of sound.
The guiding principle is smoothness. Stepwise motion (moving by a second) is preferred because it sounds singable and maintains the melodic identity of each voice. Leaps are acceptable, especially in the bass, but large or repeated leaps make a voice feel angular and hard to follow. The "singability test" is practical: could a real choral singer perform this line with ease and expression?
The most famous prohibition is parallel perfect fifths and parallel perfect octaves. When two voices both move in the same direction and stay a perfect fifth (or octave) apart, their independence collapses — the listener hears them as one voice, not two. This matters because four-part writing is a texture of four distinct lines; anything that merges two voices undermines the entire design. Contrary fifths — where one voice goes up and one goes down and they happen to arrive at a fifth — are fine, because the independent motion is audible.
The four motion types give you a vocabulary for thinking about voice pairs: contrary motion (opposite directions) is safest and most independence-preserving; oblique motion (one voice holds, one moves) is also unambiguous; similar motion (same direction, different interval) is usually fine but requires care at perfect intervals; parallel motion (same direction, same interval) is the one that must be managed most carefully. In practice, a good voice leading passage mixes all four types to keep the texture varied and each line interesting.
Studying Bach's four-part chorales is the single best way to internalize these principles. Track any two voices through a chorale and notice how rarely they move in parallel for more than one step, how the bass leaps freely while upper voices move by step, and how phrase endings use contrary motion to create strong closure. The rules are not arbitrary — they are the systematic description of what made Bach's textures sound so alive.
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