Notes and intervals
Tritone
A tritone is the interval of six semitones, three whole steps, as from C to F#: it splits the octave in half and creates the tension of dominant seventh chords.
What is a tritone?
A tritone is an interval of 6 semitones, three whole steps: C, D, E, F#. Depending on spelling it is an augmented fourth (C-F#) or a diminished fifth (C-G♭). The only tritone between natural notes is F-B (or B-F).
It splits the octave exactly in half: inverted, a tritone is still a tritone (C-F# and F#-C are both 6 semitones). It is the most unstable interval in the scale, which is exactly what makes it useful. Medieval theorists nicknamed it diabolus in musica.
How do you play a tritone on guitar?
- Next string, one fret up: C at the 3rd fret of the 5th string, F# at the 4th fret of the 4th.
- From the 3rd to the 2nd string, two frets up: C at the 5th fret of the 3rd string, F# at the 7th fret of the 2nd.
- Same string, 6 frets up: open low E, then B♭ at the 6th fret.
Because it is symmetrical, the same shape moved 6 frets gives you the same two notes swapped. Black Sabbath's song Black Sabbath and the intro to Purple Haze are built on this sound.
Why does the tritone make chords move?
In a dominant seventh chord, the tritone sits between the third and the seventh. G7 is G, B, D, F: B and F form the tritone. To release, each note moves by a semitone: B rises to C, F falls to E. The result is a C chord.
Play it with two fingers: F at the 3rd fret of the 4th string and B at the 4th fret of the 3rd string. Resolve to E (4th string, 2nd fret) and C (3rd string, 5th fret). Those two notes are the guide tones of G7. You also find the tritone in the diminished chord (B, D, F) and the half-diminished Bm7♭5.
Example: the tritone substitution
G7 and D♭7 share the same tritone: F and B (spelled C♭ in D♭7 = D♭, F, A♭, C♭). So one can replace the other. In a ii-V-I in C, Dm7, G7, Cmaj7 becomes Dm7, D♭7, Cmaj7, and the bass walks down chromatically (D, D♭, C).
Exercise: move your two-finger tritone grip down one fret, to E (4th string, 2nd fret) and B♭ (3rd string, 3rd fret). That is the tritone of C7 and G♭7; resolve it to F (3rd fret) and A (2nd fret) to land on F. This is the idea behind tritone substitution, which the chord substitutions tool applies to your progressions with playable voicings.
Key takeaways
- Tritone = 6 semitones = three whole steps, exactly half an octave.
- Augmented fourth or diminished fifth, depending on spelling.
- It carries the tension of the dominant seventh and resolves by half steps.
- Two dominant chords a tritone apart share the same tritone.
Frequently asked questions
Why is the tritone called the devil's interval?
Medieval theorists found it hard to sing and harsh, and avoided it in melodies, which earned it the nickname diabolus in musica. Today it is everywhere, from blues and jazz to metal.
Which chords contain a tritone?
Dominant sevenths (G7: B-F), diminished triads (Bdim: B-F), half-diminished chords (Bm7♭5) and diminished sevenths (Bdim7, which holds two: B-F and D-A♭). A plain major or minor triad has none.
How many frets is a tritone on guitar?
Six frets on the same string. On the next string up it is one fret higher than the starting note, and two frets higher between the 3rd and 2nd strings.
Related terms
Practise in the workshop
Take it from theory to the fretboard
Open the workshop tools and see this idea across the whole neck. Free account, no card needed.