Lesson 63 · All 12 keys

Polychord (Slash Chord) Trainer

Learn how a Polychord / slash chord is built one semitone-count at a time — a major triad (Lesson 8) rooted a whole step above the bass note, stacked over a dominant 7th chord (Lesson 13) built on that bass note — the app’s reference voicing for "X/Y" slash-chord notation — then put it to work with three MIDI exercises: playing all 12 polychords around the circle of fourths, and 5 jazz plus 5 gospel chord progressions that show off its color, in every key.

How a Polychord / slash chord is built

A Polychord / slash chord — written / (e.g. C/) — is a 7-note chord: a major triad (Lesson 8) rooted a whole step above the bass note, stacked over a dominant 7th chord (Lesson 13) built on that bass note — the app’s reference voicing for "X/Y" slash-chord notation. Every / chord — in any of the 12 keys — is built the exact same way, by counting semitones to the right from a root note:

  1. The starting note — this is the bass note, the "denominator" of the slash chord.
  2. Build a plain dominant 7th chord (Lesson 13) on this bass note: +4 (major 3rd, 4 semitones), +7 (perfect 5th), +10 (minor 7th) — that is the "lower" chord.
  3. Then count 2 semitones up from the root — this is the root of the "upper" triad stacked on top.
  4. Build a plain major triad (Lesson 8) on that note, a whole step above the bass: +4 more semitones (6 from the root) for its 3rd, and +3 more (9 from the root) for its 5th.
  5. The combined 7-note sound — a major triad rooted a whole step above the bass, played over a dominant 7th chord — is this app’s reference polychord, transposable to any of the 12 keys.
Example — C/: start on C, count 2 semitones right to reach D, count 2 semitones more to reach E, count 2 semitones more to reach F♯, count 1 semitone more to reach G, count 2 semitones more to reach A, count 1 semitone more to reach B♭. C‑D‑E‑F♯‑G‑A‑B♭ is the C/ chord.
A polychord is really two chords at once — the notation "D/C7" literally means "play a D major triad over a C7 chord." This app fixes that relationship (a major triad a whole step above the bass, over a dominant 7th on the bass) so it can transpose to all 12 keys as one consistent "chord type," the way modern gospel reharmonizations often use it.

Try it: pick a root and build the chord step by step

Step 1 of 7
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Chord toneNoteSemitones from rootMIDI #

All 12 polychords at a glance

ChordRootUpper triad root (+2)Major 3rdUpper triad 3rd (+6)Perfect 5thUpper triad 5th (+9)Minor 7th

This MIDI exercise plays all 12 polychords, one after another, moving around the circle of fourths — each chord's root sits a perfect 4th (5 semitones) above the last one: C → F → B♭ → E♭ → A♭ → D♭ → G♭/F♯ → B → E → A → D → G → back to C. Every chord is played as a full 7-note Polychord / slash chord (root (bass), upper triad root (+2), major 3rd, upper triad 3rd (+6), perfect 5th, upper triad 5th (+9), minor 7th together).

Chord 1 of 12
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The 12 chords, in circle-of-fourths order

#ChordRootUpper triad root (+2)Major 3rdUpper triad 3rd (+6)Perfect 5thUpper triad 5th (+9)Minor 7th

Five jazz chord progressions built around the Polychord / slash chord. Pick a progression and play it in one key or cycle through all 12.

Key of C
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Progression in C

DegreeChordNotes

Five gospel chord progressions built around the Polychord / slash chord. Pick a progression and play it in one key or cycle through all 12.

Key of C
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Progression in C

DegreeChordNotes