Four-part writing in AP Music Theory

Four-part writing is the practice of composing or realizing harmony in four independent voices (soprano, alto, tenor, bass) following 18th-century conventions for chord spelling, doubling, spacing, and voice leading, tested on AP Music Theory's figured bass and chorale harmonization exercises.

What is four-part writing?

Four-part writing means building harmony out of four separate melodic lines, labeled soprano, alto, tenor, and bass (SATB) based on their pitch position relative to each other (DES-1.C.1). Each voice is its own little melody, but together they spell out a chord progression. When you realize a figured bass or harmonize a melody on the AP exam, you're doing four-part writing.

The "rules" you learn are really 18th-century conventions, the habits of composers like Bach. They cover four things. Spelling means every chord has the right notes with the right accidentals (PIT-4.B.1). Doubling means deciding which chord member gets sung twice, since a triad has three notes and you have four voices. Default move is to double the root, though thirds and fifths work when voice leading demands it (PIT-4.B.2). Spacing controls how far apart the voices sit. Voice leading governs how each line moves to the next chord, including varying the motion between outer voices and avoiding more than three consecutive thirds or sixths between voices (PIT-4.C.1).

Why four-part writing matters in AP® Music Theory

Four-part writing lives in Topic 4.2 (SATB Voice Leading) in Unit 4, and it supports the whole cluster of learning objectives there. AP Music Theory 4.2.A asks you to identify the number and position of musical lines. AP Music Theory 4.2.B, 4.2.C, and 4.2.D ask you to apply the conventions of chord spelling, doubling, spacing, and voice leading through analysis, error detection, and actual writing, including progressions with first-inversion chords. This is also the skill that snowballs. Everything in Units 5-7 (predominant function, seventh chords, secondary dominants) gets tested through the lens of four-part writing, so the conventions you lock in here get reused on every harmony question for the rest of the course.

How four-part writing connects across the course

Chord voicing (Unit 4)

Voicing is the snapshot side of four-part writing. It asks how a single chord is arranged vertically, which note is on top, which gets doubled, how the voices are spaced. Four-part writing is what happens when you string good voicings together over time.

Outer voices (Unit 4)

The soprano and bass are the frame of any four-part texture. PIT-4.C.1 says the motion between them should vary (contrary, similar, parallel, oblique), so when you check your part writing, check the outer voices first. They carry the melody and the harmonic foundation.

Leading Tone (Units 1 and 4)

The leading tone is the classic tendency tone, and four-part writing is where its rules bite. You almost never double it, which is exactly why a vii°6 chord doubles its third instead. Doubling a leading tone would force parallel octaves when both copies resolve up to tonic.

Direct Fifths and Direct Octaves (Unit 4)

These are the sneaky errors graders hunt for in four-part writing. Similar motion into a perfect fifth or octave between the outer voices can be flagged even when there are no literal parallels, so part-writing accuracy means knowing these traps, not just the obvious parallel-fifths rule.

Is four-part writing on the AP® Music Theory exam?

Four-part writing is tested two ways. Multiple-choice questions hit error detection and convention recall, like asking which chord member to double in a root-position V chord (the root) or in a vii°6 (the third, so you avoid doubling a tendency tone). They also test motion classification, like recognizing soprano and alto moving in parallel thirds and remembering the three-consecutive-thirds limit from PIT-4.C.1. On the free-response side, the figured bass realization and Roman numeral progression questions are pure four-part writing. The CED states these exercises are notated in SATB four-voice texture (DES-1.C.1), and you're scored on correct spelling, conventional doubling, sensible spacing, and clean voice leading between every pair of voices. Most lost points come from parallel fifths and octaves, doubled leading tones, and unresolved tendency tones, so build a checking routine and run it on every chord pair.

Four-part writing vs chorale style

Four-part writing is the procedure; chorale style is a way of notating it. In chorale style, soprano and alto share the treble staff (stems up and down) while tenor and bass share the bass staff. You can also write four parts in keyboard style with three voices in the right hand. Either way, the same SATB voice-leading rules apply.

Key things to remember about four-part writing

• Four-part writing means composing in four independent voices (soprano, alto, tenor, bass), and it's the format for the AP exam's figured bass and chorale harmonization questions.

• Double the root of a triad whenever voice leading allows; thirds and fifths can be doubled when they produce smoother lines (PIT-4.B.2).

• Never double a tendency tone, which is why a first-inversion leading-tone triad (vii°6) doubles its third instead of the leading tone.

• Motion between the outer voices should vary, and you can't write more than three consecutive thirds or three consecutive sixths between any pair of voices (PIT-4.C.1).

• The same conventions apply to first-inversion chords and everything that comes later, so the rules you learn in Topic 4.2 are reused through Units 5-7.

• Before moving on from any chord pair, check for parallel fifths and octaves, correct doubling, and proper resolution of tendency tones.

Frequently asked questions about four-part writing

What is four-part writing in AP Music Theory?

It's composing or realizing harmony in four independent voices (SATB) using 18th-century conventions for chord spelling, doubling, spacing, and voice leading. It's the core skill of Topic 4.2 and the format for the part-writing free-response questions.

Is four-part writing the same as four-part harmony?

Essentially yes. Four-part harmony describes the texture (four voices sounding chords together), while four-part writing usually refers to the act of producing it. The AP exam uses the conventions interchangeably.

What note do you double in four-part writing?

Double the root of a triad whenever voice leading allows. Thirds and fifths can be doubled when they create smoother lines, but never double a tendency tone like the leading tone or a chordal seventh.

Are the four-part writing rules real rules composers followed?

They're conventions, not laws. They describe how 18th-century composers like Bach typically handled four voices, and even the CED notes exceptions, like a diminished fifth rising to a perfect fifth in the progression I-V⁴₃-I⁶. On the exam, though, you're graded as if they're rules.

How is four-part writing different from chorale style?

Chorale style is a notation layout where soprano and alto share the treble staff and tenor and bass share the bass staff. Four-part writing is the broader skill, and you could notate the same four voices in keyboard style instead. The voice-leading rules don't change either way.