Tritone Substitution or The Substitution V7 (SubV7) Chord
Tritone Substitution (labeled as subV7 in music analysis) is the substitution of one dominant chord with another dominant chord a tritone (3 whole steps) away from the original dominant chord.
“Dominant chord” is the name we give to the 5th chord (V7) in a major scale. Its structure is 1 3 5 b7. (In other words: a major chord with a 7th a whole step down from the root/8). The V chord is the chord with the most tension in the major scale.
It always wants to resolve down a 5th to the first chord (I) in the scale.
The reason why tritone substitution works is that 2 dominant chords a tritone apart, share the same 3rd and 7th.
The 3rd and 7th are the most important notes in the chord.
In the key of C, the dominant (also called the V chord) is G7. (G is 5 letters away from C… CDEFG)
When you move up 3 whole steps (6 frets) from G, you land on the note Db
The notes in a G7 chord are:
G7 = G B D F
Up a tritone from G7 =
Db7 = Db F Ab Cb/B
The above shows that both these dominant chords share the same 3rd and 7th, reversed.
The 3rd in G7 is the b7th in Db
The b7th in G7 = the 3rd in Db
Both these chords want to resolve to the same chord: C
The reason why both these dominant chords want to resolve to C has to do with the very unstable nature of the interval created by the 3rd and b7th (B and F) in these dominant chords.
The notes B and F, form themselves a tritone interval. The tritone is the most unstable interval in music. It has a lot of tension.
That tension created by these 2 notes, wants to resolve in half-step motions.
B wants to resolve up a half step to C. (The root of a C chord)
F wants to resolve down a 1/2 step to E (The 3rd of a C chord)
That is why these 2 dominant chords (G7 & Db7) want to resolve to a C chord, which consists of the notes CEG.
In conclusion: for every chord, there are 2 dominant chords that want to resolve to that chord.
1) The dominant chord up a 5th
2) The dominant chord up a half step
You can see this in following chord progressions:
Dm | G7 | C | C ||
Dm | Db7 | C | C ||
In one of the following blogs, we’ll talk about applying this to chords progressions with secondary dominants.
This is advanced harmony only taught in the top-level music schools in the world.
Knowing about the above opens up new harmonic sounds and possibilities.
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