Volume I · Chapter 6

Diatonic Harmony

MUSIC 20A · C-ID MUS 120Chapter quiz →

In the musicianship bookChapter 4: The Dominant and Compound Meter Chapter 5: The Subdominant and Three-Chord Songs Chapter 6: Minor Keys Chapter 9: Faster Reading and the Sixteenth Note Chapter 10: The Supertonic, the Submediant, and the Predominant Chapter 11: The Mediant, the Leading-Tone Triad, and the Full V7 Chapter 13: Minor-Key Progressions Chapter 25: Mode Mixture and Seventh Chords

Introduction: The Harmonic Ecosystem

A triad floating by itself has a quality but no context. To give chords meaning, we place them inside a key. Building triads using only the notes of a scale gives us diatonic harmony: seven chords, one on each scale degree, each with its own role.

Developing your own compositional voice, the kind a listener can recognize in two bars, usually begins with mastering these diatonic relationships before you start bending them.

Click any example to hear it.

Roman Numeral Analysis

We label chords in a key with Roman numerals. The numeral tells us two things at once: which scale degree the chord is built on, and its quality.

Uppercase (I, IV, V): major triads
Lowercase (ii, iii, vi): minor triads
Lowercase with ° (vii°): diminished triads
Uppercase with + (III+): augmented triads

Inversions are shown by adding the figured-bass numbers from Chapter 5: V⁶ is a V chord in first inversion, ii⁶₅ is a ii seventh chord in first inversion.

In every major key, the pattern of diatonic triads is the same:

Example 6.1. The diatonic triads of C major: three major (I, IV, V), three minor (ii, iii, vi), one diminished (vii°).

Example 6.2. The same pattern in D major. The key signature changes; the Roman numerals don't.

Diatonic Harmony in Minor

Minor keys need one adjustment. Remember that natural minor has no leading tone (Chapter 3). For strong dominant chords, composers raise 7̂ using the harmonic minor scale. So in minor, V is major and vii° is diminished, both containing the raised leading tone, written as an accidental:

Example 6.3. The diatonic triads of A minor, with G♯ raised in V and vii°: i, ii°, III, iv, V, VI, vii°.

Without the raised 7̂, the chord on 5̂ is minor (v) and the chord on 7̂ is a major VII. Both occur in minor-key music, especially in descending lines and in modal, folk, and film styles, but neither has the pull of V toward i.

Scale degree	1̂	2̂	3̂	4̂	5̂	6̂	7̂
Major	I	ii	iii	IV	V	vi	vii°
Minor (with raised 7̂)	i	ii°	III	iv	V	VI	vii°

Diatonic Seventh Chords

Adding a diatonic seventh to each triad produces seven seventh chords. Their Roman numerals show the quality: V⁷ (dominant seventh), ii⁷ (minor seventh), I^M7 (major seventh), vii^ø7 (half-diminished), and vii^°7 (fully diminished).

Example 6.4. The diatonic seventh chords of C major.

Example 6.5. The diatonic seventh chords of A minor (with raised 7̂ in V⁷ and vii^°7).

The most important by far is the dominant seventh (V⁷). Its third (the leading tone) and seventh (4̂) form a tritone, and the resolution of that tritone, 7̂ up to 1̂ and 4̂ down to 3̂, pulls the music powerfully home to the tonic. In both major and minor, V⁷ is a dominant seventh chord; in minor, vii^°7 is fully diminished and just as strong.

The Three Harmonic Functions

Every diatonic chord does one of three jobs, called its function:

Function	Chords	Role
Tonic (T)	I (i), sometimes vi (VI) and iii	Home base: stability, rest, arrival
Predominant (PD)	IV (iv), ii (ii°), ii⁷	The bridge: leads away from tonic toward dominant
Dominant (D)	V, V⁷, vii°, vii^°7	Tension: contains the leading tone, demands resolution to tonic

Chords with the same function share notes, which is why they can stand in for one another: IV and ii share 4̂ and 6̂; V and vii° share 7̂, 2̂, and 4̂.

Most tonal music, from Bach chorales to modern film scores, follows one cyclical journey, the phrase model:

Tonic → Predominant → Dominant → Tonic

T → PD → D → T

The arrows only point one way. Moving backward, from D to PD (V to IV, for example), is called a retrogression. It's common in blues and rock but avoided in common-practice style. Any function can be extended, and a phrase may stop at D (a half cadence, Chapter 10).

Example 6.6. The simplest phrase model: I (T) → IV (PD) → V (D) → I (T).

Example 6.7. An extended version: vi prolongs the tonic, ii is the predominant, and V⁷ drives home.

Example 6.8. The phrase model in A minor. Hear the G♯ in V pull up to A.

Harmonic Rhythm

Harmonic rhythm is the rate at which chords change, independent of the melody's rhythm. A hymn may change chords on every beat; a pop song may hold one chord for two whole measures. In most common-practice music, the harmonic rhythm speeds up toward a cadence, which adds to the sense of arrival. When you compose, choose your harmonic rhythm deliberately: it's one of the most powerful controls over a passage's energy.

Try It: Progression Player

Progression Player

Build a progression by clicking Roman numerals. The colors show function: tonic, predominant, dominant. The player flags retrogressions.

Key

Check Your Understanding

Chapter 6 Quiz →A new set of questions each time. Your score is sent to your instructor.Practice Worksheet (PDF)Roman numerals in major and minor, seventh chords, and harmonic function.Composing Worksheet (PDF)Compose a minor-key progression that follows the phrase model, then add a melody.

MuseScore TemplatesPhrase-Model Progression (A minor, piano)