Chord substitutions

The basic rule is to keep the root. D7 can be replaced by D13, since both start on D and serve the same dominant function; it is not replaced by A9, a different chord with a different function.

There are two typical cases: an extended chord replaces a triad — C by Cmaj7 — or an altered chord replaces one of the same type — C7 by C7♯5. In both the harmony keeps working; what changes is the colour.

The rule can be relaxed by replacing the function instead of the root: a iii chord can stand in for a I, because it shares two of its three notes.

The table is written on C so it can be read at a glance, but the relationship holds from any root: what applies to C7 applies to G7 by moving everything seven semitones.

Chords shown as links can be opened and heard; the ones in plain text are less common alterations that are not in the site’s catalog yet.

One warning: some substitutions are atonal, meaning they bring in notes outside the key. That does not make them wrong — jazz lives on them — but it pays to know when you are leaving the key, and to do it on purpose.

The same reasoning applies to melody. When improvising with arpeggios over a chord, you can arpeggiate another chord that shares its notes: instead of a C major arpeggio over Cmaj7, you can use Em7.

Nearly all the notes match. The D in Em7 is not in Cmaj7, but it does belong to the C major scale, so it does not clash — and it adds a note the chord did not have.

Here is how the most common progressions look once substituted. Compare each with its triad version in progressions: the harmonic function is identical, the colour is not.

Notice that between the fourth and the fifth only one chord changes — Am7 for A7 — and the effect is completely different: A7 stops belonging to C major and pushes toward the Dm7. That is the kind of decision substitutions put within reach.