A tritone is an interval of six semitones, exactly half an octave, between two notes. C to F# is a tritone, as is G to C#, and it is the most unstable interval in music, which is why it appears in dominant 7th chords and diminished chords.
What is a tritone?
A tritone is an interval of six semitones, exactly half an octave, and it is the most unstable interval in Western music. C to F# is a tritone, G to C# is a tritone, and B to F is a tritone. The name means three whole tones, because six semitones equal three tones, and the interval sits exactly halfway between the root and the octave, which is why it sounds so unsettled: it is as far as possible from both the starting note and its octave, with no clear direction home. The tritone has a dramatic history. In medieval music it was called the devil's interval, and singers were taught to avoid it, because its instability sounded wrong to ears trained on plainchant. Modern music uses it constantly instead: it is the engine inside every dominant 7th chord, where the 3rd and the 7th form a tritone that pulls toward resolution, and it is the defining interval of diminished chords, blues melodies and much jazz. The tritone did not change; musicians learned to love the tension it creates.
How the tritone works
A tritone can be spelled two ways, and the spelling decides its name. C to F# is an augmented 4th, because it spans four letters, C, D, E, F, and six semitones. C to Gb is a diminished 5th, because it spans five letters, C, D, E, F, G, and the same six semitones. Both sound identical on a piano, but they function differently: an augmented 4th tends to resolve outwards, with both notes moving away from each other, while a diminished 5th tends to resolve inwards, with both notes moving toward each other. In a G7 chord the tritone is B to F, a diminished 5th, and it resolves inwards to C and E in C major. The tritone is symmetrical, which gives it a special property no other interval has: it divides the octave into two equal halves, so there are only six distinct tritones in all of music, and each one is its own inversion. C to F# inverts to F# to C, which is also a tritone, and the same is true for every tritone pair. That symmetry is why diminished 7th chords, which are built from stacked tritones, can modulate so freely: the same notes can belong to several keys at once. The G7 guitar chord contains the tritone B to F, and the B diminished guitar chord is built around the tritone B to F as well.
Worked example — the tritone in G7. G7 is G, B, D and F. The 3rd is B and the 7th is F, and B to F spans six semitones, a tritone, spelled as a diminished 5th because it covers five letters, B, C, D, E, F. When G7 resolves to C major, the B rises one semitone to C and the F falls one semitone to E, and both notes land on chord tones of C major. That double semitone movement is the resolution of the tritone, and it is the reason the V–I cadence sounds so final. Play G7 to C on your instrument and listen for the two notes pulling in opposite directions. The key of C major shows where the movement belongs.
How to practise the tritone
Practise the tritone inside the chords that contain it, because on its own it sounds strange, and its meaning comes from the resolution.
- Play a G7 chord and listen for the tritone between the 3rd and the 7th, then resolve to C major and hear the tension release.
- Play the tritone C to F# on piano, then resolve it outwards to C to G, and inwards to B to F, noticing the two different resolutions.
- Find the tritone in the 12-bar blues progression in C major, where every dominant 7th chord contains one.
- Sing a tritone above a root note, then sing the resolution, aiming to feel the pull toward the note a semitone away in either direction.
- Use the interval calculator to find the tritone above any root, and check whether it is spelled as an augmented 4th or a diminished 5th.
Common mistakes
- Avoiding the tritone entirely — Beginners sometimes avoid the tritone because it sounds wrong on its own, but it is essential to dominant 7th chords, diminished chords and blues. Learn to use it and resolve it, rather than leaving it out.
- Spelling the tritone wrong — C to F# is an augmented 4th and C to Gb is a diminished 5th. The spelling matters because it tells other musicians which way the interval wants to resolve, so count the letters before you write it.
- Leaving a tritone unresolved — A tritone creates tension that expects a resolution. Leaving it hanging at the end of a phrase sounds unfinished, unless that is a deliberate effect, so resolve it or move on quickly.
Quick reference
This table lists the tritone above six roots, spelled both ways, so you can see that the same six semitones can be an augmented 4th or a diminished 5th depending on the letter count. Each row holds the same pitch twice, written with different letter names, and the two spellings resolve in opposite directions.
| Root | Tritone (augmented 4th) | Tritone (diminished 5th) |
|---|---|---|
| C | C – F# | C – Gb (F#) |
| G | G – C# | G – Db (C#) |
| D | D – G# | D – Ab (G#) |
| A | A – D# | A – Eb (D#) |
| E | E – A# | E – Bb (A#) |
| B | B – F | B – F |
Play the table on piano, one row at a time, and resolve each tritone in both directions: the augmented 4th outwards and the diminished 5th inwards. When you can feel the difference between the two resolutions, you understand the tritone, and you will start hearing it inside every dominant 7th chord you play.
Frequently asked questions
What is a tritone?
A tritone is an interval of six semitones, exactly half an octave, between two notes. C to F# is a tritone, and so is G to C#. It is the most unstable interval in Western music, and it is the engine of the dominant 7th chord.
Why is the tritone called the devil's interval?
Medieval musicians called it diabolus in musica, the devil in music, because its instability sounded wrong against the plainchant they sang. The name stuck even though modern music uses the tritone constantly, in blues, jazz and film scores.
Is a tritone an augmented 4th or a diminished 5th?
It can be either, depending on the spelling. C to F# spans four letters, so it is an augmented 4th; C to Gb spans five letters, so it is a diminished 5th. Both span six semitones and sound identical, but they resolve in different directions.
Where does the tritone appear in music?
Inside every dominant 7th chord, between the 3rd and the 7th, and inside every diminished chord, between the root and the 5th. It also appears in blues melodies and in the locrian mode, which is built around it.
How do you resolve a tritone?
By moving both notes by a semitone: an augmented 4th resolves outwards, with the notes moving apart, while a diminished 5th resolves inwards, with the notes moving together. In G7 the tritone B to F resolves inwards to C and E in C major.