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Using substitute chords is a common practice that spices up chord changes and often makes melodies sound more “modern.” The most common chord substitution you see is the tritone sub. Here I’ll lay out what it is, and how it can be used.

For a basic primer on harmonic tendencies and the polarity of notes, see “I-IV-V Harmony, part 2.” As was discussed in that article, the V chord contains the interval of a tritone between the 3rd and 7th of that chord. These two notes, when played together, want to resolve to the root and 3rd of the I chord.

Ex: The G7 chord in the key of C contains the tritone B-F, which wants to resolve to the C-E of the C major chord. Now, that same interval can be found in the dominant chord built a tritone from the G7 chord (a C#7 chord).

Definition and Disambiguation
Tritone: the interval of a diminished (flat) 5th or an augmented (sharp) 4th. However you want to look at it, it’s the same note. Ex: a tritone from C is F# or Gb.

In this article, I’m using the word ”tritone” in two contexts: one to refer to the interval of itself, and the other to refer to the chord substitution. If I’m talking about the interval itself, I will only use the word “tritone,” whereas if I’m talking about the chord substitution, I’ll say “tritone substitution,” “tritone sub,” or just “sub.”

What It Is and Why It Works

The tritone substitution shares the same harmonic relationship to the “home” chord (the I) as the standard V chord does, since it contains the same tritone. See Figure 1 below. Note: in this example, I’m notating the note F enharmonically as E# in the sub.

How It Is Used

Obviously, this chord doesn’t exist in a vacuum. It is always applied in a harmonic context. The most common context would that of the good old II-V-I progression. In this context, a good reason for using the sub is to create smoother, chromatic motion from the II chord, through the sub of the V, to the I. In Figure 2, notice how the roots of the three chords are jumping around a lot. There are ways to get around this with voicing, but note how with the sub, the roots move a lot smoother. There’s also more color in the sub chord, because you’re bringing in tones that aren’t part of the key (C in this case).

The same principle can also be applied to the II chord, creating a whole progression that comes from another key. Using the sub on a II chord doesn’t have the benefit of having common tones with the chord you’re substituting, but once again it can add some more chord coloring to the song.

II Chord Tritone Subs
You can take the standard II-V-I (see Figure 1) and use the tritone subs for both the II and the V, resolving to the one. Alternatively, you could only use the sub on the II chord and resolve it to the standard V, resolving to the one. These are both in Figure 3.

The second option puts the chromatic motion between the II and the V, instead of the V and the I, leaving the standard V-I motion intact. Which one you use is entirely up to your taste.

The Principle Applied

Here are the first 4 bars of Cole Porter’s “Could It Be You,” an old standard with some really pretty changes. Note the chromatic motion in bar 4. Porter wrote that. By applying the tritone sub to some other chords in the progression, a smooth and colorful effect is achieved.

Figure 4-A is the original progression. Figure 4-B uses the tritone sub for the D7 on bar 2. Since the melody has an E at that moment, I wouldn’t want to use the pure tritone sub of Ab7 (aka G#7), since that has an Eb (D#). Instead, I modified it a little bit, sharping the 5th of the chord, to coordinate with the melody.

Alternative Notation

There are other ways you might see the tritone sub notated, or other ways you yourself might want to notate them if you’re arranging or composing. See Figure 5: The basic sub is C#7, but there are two other ways it could also be written. The tritones are indicated with the bracket.

Conclusions…and a quick note for soloists

These subs can be used to make old standards sound more modern and colorful, or you can use them in arranging or composing. It’s a nice thing to know about, if you’re looking to get some more color into your playing or your pieces. And it’s fairly easy to do, because you’re still working with the same harmonic structure. Just take your standard V chord, go a tritone away, and build a dominant chord on that instead.

And that note for soloists: Even if the rhythm section isn’t playing the tritone sub, you can use it in your solo and it will sound awesome.

more articles by Brien Henderson

• Anatomy of the Blues Scale
• A Great Site for Old Music
• Every Musician Should Read This
• Saxes: Work Your Pinkies!, part 1
• Writing Your Own Music: How To Get Started
• Intro to chords in Jazz
• Subdivide. It Pays Off