A Bassist’s Guide to Chord Substitutions, Part 2

In Part 1 of this two-part series, we talked about diatonic chord substitution, which replaces one chord with another chord that shares at least two of the same notes. But there are other substitution methods that are based on shared notes. In this posting, we’ll look at the ways a guitarist or pianist might use dominant chord and secondary dominant substitutions.

TRITONE SUBS

A dominant chord substitution replaces the dominant chord (the fifth degree of the key, the V7) with another dominant chord a tritone (three whole steps) away.

In a I–IV–V (E–Ama7–B7) chord progression in the key of E, for example, the dominant chord is B7, and a tritone away is the F7. Dominant chords set us up to resolve to the tonic, also known as the I chord (in this case, E major). Dominant chord substitution works because the “tritone sub,” sometimes called the “subV,” also pulls us toward the tonic.

Notice that B7 and F7 have two notes in common: A is the seventh of B7 and the third of F7, while F is the fifth of B7 and the root of F7. Both chords contain the same tritone interval: D# – A in B7 and A – D# in F7.

B7:   B    D#    F      A

F7:    F      A      C    D#

Both chords resolve nicely to E major (E–G– B–D#). B7 already has B and D#; the F# resolves to G, and the A resolves to B. The F7, which already has D#, resolves the F to E, the A to G, and the C to B.

If you’re accustomed to the usual V7–I resolution, the tritone sub may sound “spicy,” but in time, you might develop a taste for this dominant chord that’s a half-step up from the root. For example, have a listen to this vi–ii–V–I in E (C#mi7–F#mi7–B7–Ema7) chord progression …

… and then compare it to the same progression when there’s a tritone sub for the V chord (so that B7 becomes F7), which changes the progression to C#mi7–F#mi7–F7–Ema7.

When you substitute the B7 in E major to an F7, you are playing a chord that’s not in the key, so be mindful that the new chord doesn’t clash with the song’s melody.

SECONDARY DOMINANTS

Now that we’ve heard how interesting it can be to use the tritone of a dominant chord, let’s use the dominant of a dominant chord. In the key of G, for example, we’d replace the dominant chord (D7) with a dominant chord based on the fifth of D7, which would be A7.

Here’s a ii–V–I (Ami7–D7–G) chord progression in G …

… and here’s what it sounds like if we substitute the D7 for an A7, which makes the progression Ami7–A7–G.

Both the dominant chord and the secondary dominant chord pull toward the G major (G–B–D–F#). The D7 (D–F#–A–C) shares G major’s D and F#, the A resolves to G, and the C goes to B. Similarly, in A7 (A–C–E–G), the G stays constant as the A becomes G, the C becomes B, and the E becomes F#.

Instead of substituting the V for its secondary dominant, some jazz musicians add it, placing the sub in front of the V. For example, here’s a ii–V–I chord progression in G major (Ami7–D7–G) …

… and here, adding an A7 — the secondary dominant of the D7 — changes the progression into Ami7–A7–D7–G.

You can use secondary dominants to replace, precede, or resolve to other chords, too. In the key of G, for example:

The secondary dominant of the ii chord (“V of ii”), Ami7, is E7.

The secondary dominant of the iii chord (“V of iii”), Bmi7, is F#7.

The secondary dominant of the IV chord (“V of IV”), Cma7, is G7.

The secondary dominant of the V chord (“V of V”), G7, is D7.

The secondary dominant of the vi chord (“V of vi”), Emi7, is B7.

Songwriters use secondary dominants to add excitement, delay resolution, change key or go to a new section of a song. To add pizzazz to a I–vi–ii–V in G, try adding a secondary dominant that resolves to the vi, which changes the progression from G–Emi–Ami–D7 to G–B7– Emi–Ami–D7. Here’s the original …

… and the same progression with the B7 substitution:

You can take this a step further by swapping the ii chord (Ami) for a tritone sub (E♭7), which leads smoothly into the V (D7). For example, here’s a G–B7–Emi–E♭7–D7 progression:

It can be extremely helpful to know what your keyboardist or guitarist is doing regarding substitutions. If, for example, you see a dominant chord that’s not in the key of the song, consider that it might be a secondary dominant, and if you see a dominant chord a half-step from the root, it’s probably a tritone sub. If you aren’t sure, ask!

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