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Four-part writing (soprano, alto, tenor, bass) is the traditional standard for harmonic composition and analysis. Mastering proper doubling, spacing, and voice leading in four parts develops fundamental skills applicable to all harmonic composition. The constraints of four-part writing—voice ranges, movement rules, and spacing conventions—train composers to balance voice independence with overall blend and unity.
Begin with simple diatonic progressions, focusing on one rule at a time. Analyze Bach chorales to observe how masters apply these rules flexibly in context. Compose and arrange progressions, gradually increasing complexity.
All voice-leading rules must be followed without exception; rules are learned principles that can be broken strategically for musical effect when justified. Perfect fourths between outer voices are always forbidden—they are acceptable as long as the bass is not the root of a chord.
Four-part writing assigns every harmony to four independent melodic lines — soprano, alto, tenor, and bass — named after the four human voice ranges. You already know how to identify chord inversions (which note is in the bass) and the basic doubling rules (which chord tone to double for fullness and clarity). Four-part writing pulls those concepts together into a complete system: at every moment, four voices must produce a valid chord while each one traces a coherent melodic line through time.
The vertical dimension is what you hear at any given beat: which chord is sounding, what inversion it's in, and whether the voices are spaced properly. Spacing rules keep the texture balanced — the three upper voices (soprano, alto, tenor) should generally stay within an octave of each other, while the bass can sit further below. The horizontal dimension is each voice's melodic path: it should stay within a comfortable range, prefer stepwise motion, and avoid awkward leaps. A perfect authentic cadence in four parts isn't just a V–I chord change — it's four voices each arriving on their chord tones in the most efficient and singable way possible.
The classic errors in four-part writing are parallel fifths and parallel octaves — when two voices move in the same direction by the same interval, landing on a fifth or octave. These are prohibited because they collapse two independent lines into a single, less interesting one: the voices stop behaving as separate melodic entities. The rule against parallel fifths isn't arbitrary; it enforces the independence that makes polyphony interesting. Similarly, the prohibition on hidden fifths/octaves in the outer voices (soprano and bass moving in the same direction to a fifth or octave) prevents a similar effect at the most exposed part of the texture.
Learning four-part writing from Bach chorales is the standard approach for a reason: Bach wrote hundreds of them, each demonstrating the same principles applied to a different harmonization. Analyzing a Bach chorale, you'll see that he almost never makes the awkward choices — each voice moves with a minimum of leaps, common tones are held between chords, and dissonances resolve by step. These aren't mathematical accidents; they reflect a deep internalization of what sounds natural to singing voices. The rules of four-part writing are, at their core, rules about what human voices can do comfortably and expressively. Understanding this transforms them from arbitrary constraints into a logical grammar of vocal music.
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