Blues, and the Stuff We Didn't Cover

The 12-Bar Blues

The blues has a standard form, and it’s remarkably simple:

12-bar blues in C on the Harmony Wheel

Three chords: I, IV, and V. Twelve bars. That’s the skeleton of the blues — from Robert Johnson to B.B. King to Stevie Ray Vaughan to every blues jam session happening in every bar on Earth right now.

But notice something strange: the I chord is a dominant seventh. In functional harmony, only the V chord is dominant. The I chord is supposed to be major — stable, resolved, home. In the blues, the I chord is I7. It has a flat seventh. It shouldn’t work — a dominant chord on the tonic should want to resolve somewhere else. But in the blues, it just… sits there. Comfortably. Defiantly.

The blues doesn’t care about your rules.

Blue Notes and the Blues Scale

The blues scale is a six-note scale built from the minor pentatonic with one added note — the flat fifth (also called the sharp fourth or the blue note):

In C: C – E♭ – F – F#/G♭ – G – B♭

That ♭5 is the sound of the blues. It’s the note that bends, that wails, that sits between the cracks of the piano keys. On a guitar or a voice, you can slide into it — it doesn’t have to be precisely in tune. In fact, it shouldn’t be. The blue note lives in the space between minor and major, between sadness and defiance.

The blues scale works over all three chords of the 12-bar blues. That shouldn’t be possible — a single scale over changing chords — but the blue notes have a way of bending to fit whatever’s underneath them. The E♭ in the scale clashes beautifully with the E♮ in the I7 chord. That clash is the blues. Is the blues in major or in minor? The answer is yes. It lives in the crack between the two.

The Dominant Paradox

What makes blues harmony so interesting from a theory perspective: every chord is dominant. I7, IV7, V7 — they’re all dominant sevenths. In functional harmony, that would mean they’re all trying to resolve somewhere. But in the blues, dominant quality is just the default sound. It’s not about resolution — it’s about color, weight, and grit.

This is why the blues sits outside the functional harmony framework we’ve been building. It uses the same chords, but the rules of engagement are different. The dominant seventh isn’t a wallet pointing you home — it’s just the way chords sound in this genre.

Understanding this is liberating. It means you can use dominant sevenths as color — not just as functional signposts — whenever you want a grittier, earthier sound.

And remember the diminished chord’s “ninth resolution” from last chapter — where a diminished chord can resolve to the major chord on its own root? That’s happening in the blues too. When you play C in the right hand over F7, the E♭ in F7 creates a flavor that sounds almost like C diminished resolving into C major. The blues lives in the crack between these identities — major, minor, diminished, dominant — all at once.

Tritone Substitution

Remember the wallet analogy? A dominant seventh chord has an ID — its third and seventh. Those two notes form a tritone, and they tell you exactly where the chord wants to go.

Here’s the key: the tritone is the only interval (besides the octave) that inverts to itself. Flip a tritone upside down and you get… another tritone. Most people assume the midpoint of an octave is a fifth — it feels intuitive — but it’s not. It’s the tritone. Six semitones up, six semitones down. The same distance in both directions.

This has a wild consequence. Take G7: its third is B, its seventh is F. That B–F tritone is the wallet. Now flip those roles — make B the seventh and F the third. What dominant chord has F as its third and B(C♭) as its seventh? D♭7.

G7 and D♭7 share the same tritone — the same wallet, the same ID. That means D♭7 can substitute for G7. Anywhere you’d play G7 → C, you can play D♭7 → C instead. The bass moves by half step (D♭ → C) instead of by fifth (G → C), creating a smooth, chromatic resolution.

Tritone sub: I → ii → ♭II → I on the Harmony Wheel

Tritone substitution is all over jazz, bossa nova, and sophisticated pop. It sounds “fancy,” but the mechanism is simple: two dominant chords share the same wallet and can therefore swap places.

Passing Chords

A passing chord is any chord that connects two more important chords via stepwise motion — usually chromatic (half steps). The passing chord doesn’t have its own structural role; it’s just getting you from A to B smoothly.

In the blues, you’ll often hear: I → #Idim → ii → V. That #Idim is a passing chord — it fills the gap between I and ii with a half step in the bass. We met passing diminished chords in Chapter 9. In the blues, they’re everywhere.

Passing chords are like stepping stones in a stream. They’re not destinations — they’re the smooth path between destinations.

What We Didn’t Cover

Twelve hours is a lot of ground, but it’s also a starting point. Here’s what’s waiting when you keep going:

• Extensions: 9ths, 11ths, 13ths — adding more notes on top of seventh chords for richer color
• Altered scales: scales built on dominant chords with raised or lowered 9ths, 11ths, and 13ths — the language of modern jazz
• Counterpoint: the art of writing multiple independent melodies that harmonize with each other — what Bach spent his life perfecting
• Orchestration: how different instruments combine to create color, texture, and depth
• Non-Western systems: tuning systems, scales, and rhythmic frameworks from outside the Western tradition — microtones, ragas, polyrhythmic structures

The 10 Chord Toolkit, the form analysis, the ear training, the voice leading, the rhythmic awareness — these are all foundations. They don’t expire. Everything you learn from here builds on what you’ve already internalized.

“Keep going” doesn’t mean another course. It means Music Theory Gym — the weekly residency where we take these concepts and apply them to real music in real time. You’ve got the vocabulary now. The gym is where you use it: analyzing songs, spotting progressions by ear, building arrangements, and asking the questions that only come up once you know enough to be curious. If you’re a BKS resident, you already have access. Show up and play.

The Harmony Wheel

One last reminder: the Harmony Wheel is your companion for everything in this course and beyond. Use it to visualize progressions, test ideas, hear chord functions, and build intuition. It supports all the chord types we’ve discussed — load up a progression and listen. Theory is a vehicle for talking about music. The Harmony Wheel is a vehicle for hearing it.

What to Practice

• Play a 12-bar blues in any key. Just I7, IV7, V7. Put it under your fingers. Loop it. Feel how the dominant chords sit differently than they do in functional harmony.
• Try soloing with the blues scale over the 12-bar form. Let the E♭ clash with the E♮ in the I7 chord. That’s not a mistake — that’s the blues.
• Try a tritone substitution: wherever you’d play V7, play ♭II7 instead. Hear the chromatic bass resolution.
• Pick any concept from this course that felt shaky and revisit it. The class summaries, the Harmony Wheel, and Music Theory Gym are all there for exactly this purpose.