Diatonic Harmony, Function & Voice Leading

You’ll be able to

Label diatonic triads in major and minor with Roman numerals
Classify chords by tonic, predominant, and dominant function
Apply core SATB voice-leading rules and spot common violations

Diatonic triads and Roman numerals

Build a triad on each degree of a scale and you get the diatonic triads, labeled with Roman numerals whose case shows quality: uppercase for major, lowercase for minor, lowercase with ° for diminished. In a major key the pattern is fixed: I ii iii IV V vi vii°. In C major that is C, Dm, Em, F, G, Am, B°. In minor, harmonic minor supplies a leading tone so the crucial chords become V (major) and vii° (diminished), giving the pull that natural minor lacks.

Harmonic function: tonic, predominant, dominant

Chords group into three functions that describe their role in a progression. Tonic (I, and the tonic-substitute vi) is home — stable, restful. Dominant (V and vii°) is tension that wants to resolve to tonic; both contain the leading tone (ti) and the tritone. Predominant (ii and IV) is the bridge that prepares the dominant. Functional harmony flows in one strong direction: tonic → predominant → dominant → tonic (T–PD–D–T).

SATB voice leading: the core rules

Four-part writing distributes a chord across soprano, alto, tenor, and bass. A few rules keep the voices independent and smooth: (1) No parallel fifths or octaves — two voices a fifth or octave apart must not move to another fifth or octave in the same direction. (2) Resolve the leading tone up to the tonic, especially in an outer voice. (3) Resolve the chordal seventh down by step. (4) Keep upper voices within an octave of their neighbor, move by the smallest interval, and hold common tones. (5) Do not double the leading tone.

Diatonic triads and function in major

I ii iii IV V vi vii° → T: I, vi · PD: ii, IV · D: V, vii°

Case shows quality (I major, ii minor, vii° diminished). Functional flow is T → PD → D → T; the dominant resolves the leading tone up to the tonic.

Worked example

In G major, spell the V chord, name its function, and state how its leading tone resolves.

1.The fifth degree of G major is D, so V is a triad built on D.
2.Spell it diatonically: D–F♯–A, a major triad (V is always major in a major key).
3.V has dominant function — it contains the leading tone F♯ (scale degree 7) and drives toward tonic.
4.The leading tone F♯ resolves up by half step to G, the tonic, as V moves to I.

Answer: In G major, V = D–F♯–A (D major), a dominant-function chord. Its leading tone F♯ resolves up a half step to G when V progresses to I.

Checkpoint

In a major key, which chord has dominant function and is built from scale degrees 5–7–2 (containing the leading tone)?

Watch out

The most penalized voice-leading error is parallel fifths or octaves. If two voices form a perfect fifth (or octave) and both move in the same direction to another perfect fifth (or octave), it is a parallel — even a step apart. Check every pair of voices between adjacent chords, especially soprano-bass.

Checkpoint

The bass sings C then D, and the soprano sings G then A, both moving up by step. What voice-leading error is this?

On the exam

On part-writing questions, resolve tendency tones without fail: the leading tone (ti) rises to do, and the chordal seventh falls by step. In a V7–I in C, B (ti) goes to C and F (the seventh) goes to E. Missing either resolution is an automatic deduction.

Answer the 2 checkpoints as you read.