Pianist Terry Seabrook’s Jazz Tip of the Month No. 9

So What Is A Tritone?

In my previous jazz tip (No. 8) I mentioned the tritone as an interesting idea in jazz harmony.

Tritone is the jazz term for the interval (musical pitch distance) of three whole tones (or whole steps). This is also known as a diminished fifth (or flattened fifth) or an augmented fourth (or a sharpened fourth). It is an imperfect dissonance and in a conventional harmonic context requires resolution. In the middle ages it often went under the description of the devil’s interval (diabolus in musica).

If the tritone is three whole tones then it is also six semitones (or six half steps) which is half an octave (12 semitones).

Because it is half an octave the inversion of a tritone is a tritone. (This doesn’t happen with other intervals. A third, for example, inverts to a sixth: C to Gb is a tritone, the inversion is Gb to C which is also a tritone

Although if you label it as an augmented fourth it inverts to diminished fifth. It is interesting to remember that inverted intervals always add up to nine: fourth to fifth, third to sixth, second to seventh, and octave to unison.

So there are six pairs of tritones (which incidentally are opposites on the circle of fifths):

· C-Gb (or C-F#)

· Db-G (or C#- G)

· D-Ab (or D-G#)

· Eb-A (or D#- A)

· E-Bb (or E-A#)

· F-B

Learn these pairs (from both sides) because they crop up all the time in jazz harmony. And try singing them, which is hard but a good tip is to think of the first two notes from the song Maria from West Side Story by Leonard Bernstein.

The first way to apply this harmonically is to substitute dominant seventh chords for their tritone relatives (tritone substitution). An important instance of this is tritone substitution in the famous II – V – I progression

Eg in II – V – I such as Gm7 – C7- Fmaj7 play Gb7 instead of C7 

This now becomes: 

Gm7 – Gb7 – Fmaj7. 

And could now be described as:

II – bII  – I 

This substitution works because C7 and Gb7 share the same two notes for their third and seventh (the two key harmonic tendency tones) in this case Bb and E (Fb)

Also, the substituted chord (Gb7) looks and sounds very much like C7alt.

Another example is tritone addition:

Gm7 – C7 – Gb7 – Fmaj7

This has a more chromatic or altered sound which is typical of jazz harmony from the bebop era onwards, although interestingly the first recorded use of this in improvisation is often attributed to Coleman Hawkins on his famous 1939 recording of Body and Soul.

Further substitution possibilities concern the other chords in the progression. So substituting the II chord we get:

Dbm7 – C7 –Fmaj7 or Dbm7 – Gb7 – Fmaj7

And substituting the I chord we get:

Dm7 – G7 – Bmaj7 or Abm7 – Db7 – Fmaj7

Work this out for other keys (The sky is the limit).

Terry Seabrook