In the previous article, you experienced how adding just one note to a triad changes the feel of a progression. This time, we'll learn a technique for swapping a chord itself with another chord that shares the same role — chord substitution.
⚽ Teammates in the Same Position
In the diatonic article, we compared the seven chords to a soccer team. In the progressions article, we learned that the team is divided into three role groups.
| Role | Members | Job |
|---|---|---|
| Tonic (T) | I (Captain), iii (Link Player), vi (Vice-Captain) | Stability & landing |
| Subdominant (S) | IV (Attacking Midfielder), ii (Reflective Midfielder) | Motion & floating |
| Dominant (D) | V (Striker), vii° (Specialist) | Tension & pull toward home |
A substitute chord means swapping a member within the same role group. In soccer terms, it's a "same-position substitution."
Swapping one striker for another doesn't change the team's tactics — but it does change the playing style. Chord substitution works exactly the same way.
🔄 Why Does Substitution Work?
Chords in the same role group can be swapped because two of their three notes overlap.
As we learned in the chords article, when two out of three notes are shared, the foundation of the sound is the same. That's why a substitution doesn't break the "drama" of the progression.
Let's look at this in the key of C major:
| Swap | Chord ① | Chord ② | Shared Notes |
|---|---|---|---|
| I ↔ vi | C (C・E・G) | Am (A・C・E) | C, E |
| I ↔ iii | C (C・E・G) | Em (E・G・B) | E, G |
| IV ↔ ii | F (F・A・C) | Dm (D・F・A) | F, A |
| V ↔ vii° | G (G・B・D) | Bdim (B・D・F) | B, D |
Because two notes overlap, the impression is "similar, but slightly different." That "slightly different" is the key to changing the expression of a progression.
And there's one more thing. When a chord changes, the root note (bass note) changes too. For example, the jump from C→F (C to F) becomes the smooth stepwise motion of C→Dm (C to D). Substitution lets you shape not just the expression, but also the flow of the bass line.
🎭 Substitute Chords in Practice — 3 Classic Patterns
Pattern 1: I → vi (Bright → Bittersweet)
The most common substitution. Swapping the Captain (I) for the Vice-Captain (vi) turns a bright stability into a stability tinged with bittersweetness.
Original: C → F → G → C
Substituted: C → F → G → Am
Just changing the final C to Am. The structure (T→S→D→T) is exactly the same, yet the ending shifts from "happy ending" to "ending with lingering emotion".
In pop music, when you want "just a touch of sadness at the end of the chorus," this I → vi swap is the go-to technique.
Pattern 2: IV → ii (Floating → Reflective)
A swap within the subdominant group. The open, floating feel of IV (F) becomes a more inward, contemplative mood with ii (Dm).
Original: C → F → G → C
Substituted: C → Dm → G → C
F gives you that "suddenly the view opens up" feeling, while Dm gives a "pausing to think" feeling. Both are subdominant, but their personalities are opposite.
Pattern 3: V → vii° (Classic → Thrilling)
Swapping the Striker (V) for the Specialist (vii°). The confident tension of V (G) becomes an unstable, thrilling tension with vii° (Bdim).
Original: C → F → G → C
Substituted: C → F → Bdim → C
This is an advanced flavor. Overuse makes things unstable, but one well-placed use can really catch the listener's attention.
Note: The Bdim triad has a classical sound and is rarely used on its own in pop music. In practice, it's more common to use the 7th chord version — Bm7♭5 — or to simply change the bass note of G to B, creating G/B (a slash chord), as introduced in the next section.
🎨 "Dressing Up" Your Progressions
The essence of substitution is changing only the expression while keeping the structure (drama) intact. It's like changing clothes.
Let's try "dressing up" different progressions:
| Original Progression | Substituted Version | What Changed |
|---|---|---|
| C → F → G → C | Am → F → G → C | The opening became bittersweet |
| C → F → G → C | C → Dm → G → C | The middle became reflective |
| C → G → Am → F | C → G → Am → Dm | The ending became softer |
| C → Am → F → G | C → Am → Dm → G | The subdominant turned inward |
In every version, the T→S→D→T skeleton is the same. It's the feeling of "telling the same story in a different voice."
Try dressing up the progressions you built in the progressions article. From a single progression, countless variations are born.
🔗 Combining with 7th Chords
Combine the 7th chords from the previous article with substitution, and the expressive range grows even further.
| Original Chord | Substitute | 7th Version | Effect |
|---|---|---|---|
| C | → Am | → Am7 | Soft, bittersweet landing |
| F | → Dm | → Dm7 | Gentle, reflective float |
| G | → Bdim | → Bm7♭5 | Slowly building tension |
| Am | → C | → Cmaj7 | Stylish stability |
Change the "expression" with a substitute, then add "texture" with a 7th — by combining these two techniques, an astonishing variety of progressions emerge from just seven diatonic chords.
🎛️ Experience Substitute Chords with OtoTheory
In OtoTheory, the concept of substitute chords is available under the feature name "Alternatives." While music theory textbooks call it "chord substitution," the app focuses on the action itself — "replacing a chord with an alternative that shares the same role" — using a more intuitive name.
* The "Alternatives" tab in the Build screen's Insight Engine (Pro feature): With a chord progression in place, tap any existing chord chip and the Insight Engine appears at the top of the screen. Select the "Alternatives" tab, and you'll see cards showing chords with the same harmonic function. For example, tapping Am shows suggestions like "Same tonic function, brighter" and "Same tonic function, lighter." Preview the sound, and if you like it, just tap "Replace" — try substitute chords instantly without stopping the music. What's suggested here is exactly the same-function diatonic swapping you learned in this article
* The "Chord Alternatives" section in the Insight tab: The Insight tab at the bottom of the screen lets you explore replacements more broadly. All section chord chips (Verse, Chorus, Bridge, etc.) are displayed, and selecting any chord shows not just substitutes but also 7th extensions and relative-key alternatives with detailed explanations. For example, selecting Am shows "Am7: Natural minor 7th," "Am6: Dorian-colored minor 6th," and "C: Relative major sharing the same notes" — complete with example song names (Stairway to Heaven, Smooth, etc.). Preview and replace with one tap
* Fretboard display: Compare the chord tones of the original and substitute chord on the fretboard to visually confirm that "two notes are shared"
✅ Summary
Chord substitution changes only the "expression" of a progression without breaking its "drama." Chords in the same role group share two notes, so swapping them sounds natural.
* Tonic substitution (I ↔ vi ↔ iii): Switch between brightness ↔ bittersweetness ↔ subtle color within stability
* Subdominant substitution (IV ↔ ii): Switch between open ↔ reflective floating
* Dominant substitution (V ↔ vii°): Switch between classic tension ↔ thrilling tension
* Combine with 7th chords, and the variations multiply further
* The most effective first step is to try swapping I → vi
In the next article, we'll call in reinforcements from outside the diatonic team — stepping into the world of non-diatonic chords (borrowed chords).