6 semitones · half an octave · pure 45:32 or 7:5
The tritone
Six semitones, exactly half an octave: three whole steps, hence the name. It sounds tense and unsettled, and in harmony it pulls hard toward resolving.
An augmented fourth or a diminished fifth
C to F♯ is an augmented fourth and C to G♭ a diminished fifth: the same sound on a piano, spelled two ways. Turn a tritone upside down and you get another tritone, because it splits the octave in half. Pure, it has more than one size: 45:32, 590 cents (a cent is a hundredth of a semitone), from fa up to ti in a pure major scale, and 7:5, 583 cents, between the third and the seventh of a barbershop seventh, the one this page plays.
Where you hear it
Every dominant seventh chord holds a tritone between its third and its seventh: in G7, B and F. Resolving it, B up to C and F down to E, is what makes the chord lead home. There's no well-known public-domain tune that starts with one, but you may know it from Maria in West Side Story: its first two notes leap a tritone up.
More intervals
- Minor secondOde to Joy (after the repeated first note)
- Major secondHappy Birthday (after the repeated first note)
- Minor thirdGreensleeves
- Major thirdWhen the Saints Go Marching In
- Perfect fourthAmazing Grace; Here Comes the Bride
- Perfect fifthTwinkle, Twinkle, Little Star (after the repeated first note)
- Minor sixthThe Entertainer (its first high note)
- Major sixthMy Bonnie Lies over the Ocean
- Minor seventh
- Major seventh
- OctaveTake Me Out to the Ball Game
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Questions
What is a tritone?
An interval of six semitones, three whole steps, exactly half an octave: C to F♯, or B to F.
Why is the tritone called the devil's interval?
In medieval theory it was hard to fit into the scale system and was avoided, and the Latin nickname "diabolus in musica" grew up around it later. Despite the legend, no church rule banning it has ever been found.
Is a tritone an augmented fourth or a diminished fifth?
Both: the name depends on the spelling. C to F♯ is an augmented fourth, C to G♭ a diminished fifth, and they sound the same on a piano.
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