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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