Four-part writing is the practice of composing or realizing harmony in four voices — Soprano, Alto, Tenor, and Bass (SATB) — following conventions derived from the choral and keyboard repertoire of the Baroque and Classical periods. Each voice occupies a specific range, and vertical spacing follows rules: adjacent upper voices (SAT) should be within an octave of each other, but the Bass may be more than an octave below the Tenor. Chord tones are distributed among the four voices, with the leading tone and seventh requiring specific resolutions. Four-part writing is the ideal laboratory for internalizing voice-leading principles, harmonic syntax, and the sound of common-practice tonality.
Begin by harmonizing simple soprano melodies with I, IV, and V chords, solving one chord at a time before connecting them. Use a checklist at each chord: doubled tones, voice ranges, parallel fifths and octaves, voice crossing. Study and sing through Bach chorales to internalize what correct four-part writing sounds and feels like.
Four-part writing in SATB format is the classical laboratory for everything you have learned about voice leading and harmony. Rather than thinking abstractly about chord progressions, you are now producing an actual musical texture: four simultaneous melodic lines, each with its own range and character, that together form a coherent harmonic surface. The soprano and bass define the outer frame; the alto and tenor fill in the inner structure.
The rules that govern SATB writing are not arbitrary — each one captures a principle you have already encountered. The prohibition on parallel fifths and octaves prevents two voices from merging into a single acoustic entity, destroying the independence of parts. The doubling conventions (prefer the root, avoid the third) ensure that the chord's most stable tone is reinforced, not its most active one. The spacing rule — upper voices within an octave — keeps the harmonic blend tight where the ear is most sensitive to internal dissonance, while giving the bass room to anchor from below without muddiness.
Working through a four-part harmonization requires solving several simultaneous constraints at each chord: what notes are available, how to voice them within range, where to move each voice to reach the next chord smoothly, and which doublings and spacings are permitted. The checklist approach (ranges, doubling, parallels, voice crossing, leading-tone resolution) is not a crutch — it mirrors the internalized competence that experienced composers run subconsciously. You build that intuition by solving one chord at a time until it becomes automatic.
The leading tone deserves special attention: scale degree 7 strongly wants to resolve upward to the tonic (scale degree 1). In soprano and bass, this pull is so strong that you almost never override it. In inner voices, you have slightly more flexibility — if resolving the leading tone upward would create parallel octaves with another voice, the alto or tenor may descend, but you need a clear reason. Treating this as a default rather than a rule prevents both errors (unresolved leading tones) and rigidity (refusing all exceptions).
Study Bach's four-voice chorales not just as models to imitate but as a sonic vocabulary to absorb. When you sing through them — or better, sing one voice while playing the others — you internalize what correct four-part writing actually sounds like. The rules will stop feeling like a cage and start feeling like a description of a style you can hear.
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