How do you find the tritone substitute of a chord?

Count six half steps from the root of the dominant seventh: G7 gives D♭7, A7 gives E♭7, D7 gives A♭7. Keep the chord type, a dominant seventh, and spell the new root with whichever accidental is simpler.

Does a tritone substitution change the key?

No. It leads to the same chord as the dominant it replaces, so the key stays. What changes is the colour: notes from outside the key, such as D♭ and A♭ in C, and a bass that falls by half step.

How is a tritone substitution different from a secondary dominant?

A secondary dominant is the dominant of a chord other than the tonic. A tritone substitution trades any dominant for another with the same third and seventh, and a secondary dominant can be traded as well as the plain V7.

Tritone Substitution: How It Works, With Examples

A tritone substitution swaps a dominant seventh chord for the dominant seventh whose root is a tritone away. In C, D♭7 can stand in for G7: they share the same two key notes and both resolve to C.

What is a tritone substitution?

A dominant seventh chord gets its pull from two of its notes: the third and the seventh, which are a tritone (six half steps) apart. If you replace the chord with the dominant seventh whose root is a tritone away, the new chord holds the same two notes, so it pulls toward the same place. In C major, D♭7 can take the place of G7. Both contain F and the note a half step below C, which G7 spells B and D♭7 spells C♭.

The third and seventh of G7 and of D♭7. The two chords trade roles: B is the third of G7 and F its seventh; in D♭7, F is the third and C♭, the same key as B, is the seventh.

Why does the substitute work?

The trade is what makes the resolution identical. B is the third of G7 and rises a half step to C; in D♭7 the same sound is the seventh, C♭, and it rises to C all the same. F is the seventh of G7 and falls to E; in D♭7 it is the third, and it falls to E as well. So the key does not change. The rest of the chord does: D♭7 brings D♭ and A♭ in place of G and D, two notes from outside C major, and with them a different colour.

The root moves differently too. In a ii–V–I the bass leaps by fifths, D to G to C. With the substitute it steps down by half steps, D to D♭ to C, a smooth chromatic line, and that line is a large part of why players reach for the swap.

Dm7, D♭7 and Cmaj7. The bass falls D, D♭, C, and no other voice moves more than a half step.

How is a tritone substitute written?

In numerals, subV7 is the tritone substitute of V7: in C, D♭7. It can also be read plainly as the chord on the flattened second degree, ♭II7, and the practice tool accepts either name for the same chord. In a minor key the idea is the same: in A minor, iiø7–subV7–i7 is Bm7♭5, B♭7, Am7, with the bass again falling B, B♭, A.

Can a secondary dominant be substituted too?

Yes. Every dominant seventh has a tritone substitute, a secondary dominant included. In C, V7/ii is A7 and its substitute, subV7/ii, is E♭7, which reads plainly as ♭III7. The part after the slash names the chord the dominant leads to, exactly as it does for a secondary dominant. The table gives three, each spelled in C.

Leads to	Dominant	Tritone substitute	Plain name	Shared third and seventh
C (I)	G7 (V7)	D♭7 (subV7)	♭II7	B (C♭), F
Dm (ii)	A7 (V7/ii)	E♭7 (subV7/ii)	♭III7	C♯ (D♭), G
G (V)	D7 (V7/V)	A♭7 (subV7/V)	♭VI7	F♯ (G♭), C

What is a related ii?

A dominant can be approached by its own ii, the way V7 is in a ii–V–I. The related ii of a chord is the minor seventh chord a fifth above the root of the dominant that leads to it, so the ii–V pair aims at that chord instead of the tonic. Take G as the target: its dominant is D7 (V7/V), a fifth above D is A, and the related ii is Am7, written ii7/V. In C the phrase runs Cmaj7, Am7, D7, G7, Cmaj7, which is Imaj7, ii7/V, V7/V, V7, Imaj7.

Tritone substitution