A Bassist’s Guide to Chord Substitutions, Part 1

Think of a song as a story in which the sentences (chord progressions) are made of words (chords). Chord substitutions, then, are like synonyms that can replace words without significantly changing the meaning of the sentence. And just as there’s an art to using the right word at the right time, there are several ways to skillfully exchange one chord for another. Let’s start with diatonic chord substitution, where all the chords are in the same key.

THREE-NOTE DNA

Diatonic substitution replaces one four-note chord with another four-note chord that shares three of the same notes. In a major key, the I chord shares three notes with both the iii chord and the vi chord; the IV chord shares three notes with the ii chord and the vi chord; and the V chord shares three notes with the vii chord. (Try using the mnemonic “136-426-57” to remember these relationships.)

In the key of C, for example, the I chord, Cma7 (C – E – G – B), shares triads with the iii chord, Emi7 (E – G – B – D) and the vi chord, Ami7 (A – C – E – G). The IV chord, Fma7 (F – A – C – E), has triads in common with the ii chord, Dmi7 (D – F – A – C) and the vi chord, Ami7 (A – C – E – G). The V chord, G7 (G – B – D – F), shares three notes with the vii chord, Bmi7b5 (B – D – F – A).

Let’s try substituting chords in a I-IV-V progression in E. The chords in the audio clip below are Ema7 for two bars, followed by Ama7 and B7 for one bar each, with the bass outlining each chord.

In this key, the I chord, Ema7 (E – G# – B – D#) shares three notes with the iii chord, G#mi (G# – B – D# – F#) and the vi chord, C#mi7 (C# – E – G# – B). The IV chord, Ama7 (A – C# – E – G#) shares three notes with the ii chord, F#mi7 (F# – A – C# – E) and the vi chord, C#mi7 (C# – E – G# – B). The V chord, B7 (B – D# – F# – A), shares three notes with the vii chord, D#mi7b5 (D# – F# – A – C#).

If we substitute the vi chord (C#mi7) for the I chord (Ema7), the progression becomes C#mi7 – Ama7 – B7, which sounds like this:

If we continue by substituting the ii chord (F#mi7) for the IV chord (Ama7), the progression becomes C#mi7 – F#mi7 – B7 and sounds like this:

And if we substitute the vii chord (D#mi7♭5) for the V chord (B7), we get C#mi7 –  F#mi7 –  D#mi7♭5:

Although the theory may take a moment to digest, listen to how the substitutions change the chord progressions, and think of them as colors and options at your disposal for soloing and songwriting, or for simply keeping things interesting.

THE ROLE OF THE BASS IN CHORD SUBSTITUTIONS

In most situations, the bassist’s job is to play the root of each chord, but if you’re playing improvisational music, you may have more room to try things out. Let’s take a common progression like a I-vi-ii-V (Cma7 – Ami7 – Dmi7 – G7 in the key of C).

Here’s what it would sound like if the bass substitutes the iii chord (Emi7) for the I chord (Cma7) while the keyboardist plays it straight:

If the bass also outlines the iii chord (Emi7) instead of the keyboardist’s vi chord (Ami7), it sounds like this:

We could take things further by playing the IV chord (Fma7) when the keyboardist plays the ii chord (Dmi7):

We could also play the vii chord (Bmi7♭5) when the keyboardist hits the V chord (G7).

It’s far more common, however, for other instruments to substitute chords while the bass plays the roots of the original progression. As an example, let’s use a minor key, where the chord qualities are different from a major key but the numerical relationships (“136-426-57”) stay the same. In A minor, for example, the I chord, Ami7 (A – C – E – G) shares three notes with both the III chord, Cma7 (C – E – G – B♭) and the VI chord, Emi7 (E – G – B♭ – D). The IV chord, Dmi7 (D – F – A – C) shares three notes with the ii chord, Bmi7♭5 (B – D – F – A) chord and the VI chord, Fma7 (F – A – C – E); and the v chord, Ebmi7 (E – G – B – D) shares three notes with the VII chord, Gma7.

Here’s a I-VI-III-VII groove in A minor (Ami7 – Fma7 – Cma7 – Gma7):

Listen to what happens when the keyboardist substitutes a III chord for the I chord …

… a I chord for the III …

… and a v chord for the VII.

NEW TOOLS

Chord substitutions make more colors available when soloing, give you the ability to switch things around when playing chorus after chorus of the blues (or any other progression) and prepare you for the inevitable moment when your guitarist or keyboardist changes things up. If you decide to use chord subs, though, make sure your choices don’t clash with the melody, which usually flows smoothly from chord to chord. The best way to learn is to experiment and see what works, preferably in the rehearsal room.

In Part 2, we’ll learn how to spice things up by using dominant chord substitutions, secondary dominant substitutions and tritone substitutions. Happy practicing!

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