Tritone

A musical interval spanning three whole tones, heard enharmonically as either an augmented fourth or a diminished fifth. Its six-semitone span divides the octave into two equal parts.

Musical interval: The distance in pitch between two notes, measured by frequency ratio or by steps in a musical system. The tritone is one specific interval, defined by its three-tone span.
Tritone substitution: A jazz harmony technique that replaces a dominant-seventh chord with another dominant-seventh chord a tritone away. The substitute chord shares the original’s guide tones through enharmonic reinterpretation.
Diabolus in musica: A Latin expression meaning “the devil in music,” historically associated with the tritone’s dissonant sound. The phrase captures the interval’s long-standing reputation for instability.
Perfect fourth: A diatonic interval spanning four letter names and five semitones in twelve-tone equal temperament. It differs from the augmented fourth by one semitone despite sharing the same letter span.
Whole tone: A musical interval equal to two semitones in twelve-tone equal temperament. Three whole tones make the tritone’s conventional name and span.
Dominant seventh chord: A four-note chord built from a root, major third, perfect fifth, and minor seventh. Its third and seventh form a tritone that strongly shapes its harmonic direction.
The Simpsons theme: The opening theme music composed by Danny Elfman for the animated television series The Simpsons. Its opening melody prominently features a tritone leap.
Perfect fifth: A diatonic interval spanning five letter names and seven semitones in twelve-tone equal temperament. It differs from the diminished fifth by one semitone despite sharing the same letter span.
Semitone: The smallest interval in common Western equal temperament, equal to one-twelfth of an octave. The tritone spans six semitones in twelve-tone equal temperament.
Voice leading: The movement of individual melodic lines between notes in successive chords. The tritone’s notes often resolve by contrary semitone motion in tonal voice leading.

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