Understanding Diatonic Substitution and Chord Progressions

Diatonic substitution is a powerful concept in music theory that allows composers and performers to add variety and color to their chord progressions while staying within the tonal framework of a key. By substituting one diatonic chord for another, you can create smoother voice leading, introduce new harmonic textures, or provide an element of surprise. In this article, we’ll explore the principles of diatonic substitution and analyze several chord progressions and cadences, including examples provided in both major and minor keys.

What is Diatonic Substitution?

Diatonic substitution occurs when one chord is replaced by another chord from the same key. These substitutions often work because they share common tones or similar functions within the harmonic framework. For instance:

Tonic substitutions replace chords that resolve to the tonic (I or i).
Pre-dominant substitutions replace chords leading to the dominant (V or V7).
Dominant substitutions replace chords that resolve directly to the tonic.
Chord Progressions with Diatonic Substitution
1. Major Key Progression: IV—viiº—iii—vi—(IV or ii)—(V or viiº)—I

This progression moves through a series of diatonic chords, showing how substitutions add variety:

IV → viiº: The subdominant (IV) moves to the diminished leading-tone chord (viiº), creating tension.
iii → vi: The mediant (iii) substitutes for I, leading smoothly to vi, a substitution for IV or ii.
(IV or ii) → (V or viiº): The pre-dominant IV or ii moves to the dominant V or viiº, resolving to the tonic (I).
Example in C major:

F → Bdim → Em → Am → (F or Dm) → (G or Bdim) → C
2. Minor Key Progression: i—V—I

The progression i—V—I is a basic framework in minor keys.
By substituting with i → viiº6 → i, we create smoother voice leading.
Example in A minor:

Am → G → Am or Am → Bdim6 → Am
3. Using Seventh Chords: i—V65—I and i—viiº7—I

i → V65 → I: A V7 chord with the seventh (G7 in C minor) resolves to tonic.
i → viiº7 → I: The fully diminished viiº7 adds even more tension before resolving.
Example in A minor:

Am → E7 → Am or Am → Bdim7 → Am
4. Expanding Pre-dominant Function: i—iv—V—i

i → iiº6 → V → i: The iiº6 chord substitutes for iv, creating smoother movement.
i → iiº65 → V7 → i: The iiº65 (second inversion) provides a pre-dominant flavor before V7 resolves to i.
i → VI → iiº65 → V7 → i: The VI chord acts as a substitution for iv, adding richness.
Example in A minor:

Am → Dm → E → Am
Am → Bdim6 → E → Am
Am → F → Bdim65 → E7 → Am
Deceptive Cadence and Substitutions
1. V → i Deceptive Cadence

A deceptive cadence replaces the expected tonic with vi or VI.
Example in A minor:
V → VI: E → F (VI in root position, with doubled 3rd). This creates a surprising resolution.
2. Expanded Deceptive Cadence

i → iiº6 → i64 → V7 → VI (root position with doubled 3rd):
This progression delays the resolution, adding drama before resolving deceptively.
Cadences and Substitution Techniques
1. Half Cadence

A half cadence resolves to the dominant (V).
Example: i → iv6 → V in A minor:
Am → Dm6 → E
2. Perfect Authentic Cadence

Requires V → I, both in root position.
Example: E → Am
3. Deceptive Cadence

V → VI or V7 → VI in minor:
E7 → F
V7 → bVI in major:
G7 → Ab in C major.
4. Phrygian Half Cadence

A characteristic progression in minor keys: i → iv6 → V.
Example: Am → Dm6 → E
Diatonic Substitution in Practice
Diatonic substitutions are versatile tools for creating unique harmonic progressions while maintaining the integrity of a key. They are especially useful in:

Voice Leading: Smooth transitions between chords.
Harmonic Variety: Breaking monotony by introducing unexpected resolutions.
Building Drama: Delaying resolution with substitutions like iiº or VI.
To master diatonic substitution, experiment with these progressions in different keys and apply them to compositions or improvisations. By exploring substitutions, you’ll expand your harmonic vocabulary and enhance the emotional depth of your music.

Final Thoughts

Diatonic substitution is a cornerstone of harmonic creativity, offering endless possibilities to enrich your music. Whether you’re writing classical compositions, jazz improvisations, or modern songs, these substitutions can add elegance, sophistication, and surprise. Dive in, experiment, and make these techniques your own.