Six semitones. Exactly half an octave. The engine of the dominant 7th chord, the secret of jazz substitution, and the interval medieval theorists called diabolus in musica.
Interval Mastery Series
There’s a six-semitone interval that medieval theorists called diabolus in musica — the devil in music. They didn’t actually believe Satan lived inside the interval. But they did consider it acoustically unstable enough that they wrote rules forbidding its direct use in liturgical singing. Then something strange happened — composers stopped avoiding the tritone and started building their entire harmonic system around it.
The dominant 7th chord contains a tritone, and that tritone is precisely what gives the chord its forward motion. Today the tritone opens “The Simpsons” theme, powers nearly every metal riff, and is the secret behind tritone substitution in jazz.
The Tritone in Action
Four letter-positions apart, widened by one semitone from a perfect fourth. Typically expands outward on resolution.
The same 6 semitones, spelled two ways. Spelling indicates harmonic function.
The tritone is the interval of six semitones — exactly half an octave. It sits precisely in the middle of the 12-semitone span, equidistant from both endpoints. This symmetry gives the tritone a remarkable mathematical property: inverting a tritone produces another tritone. It is the only interval that is its own inversion.
The name comes from Latin tritonus, meaning “three tones” — three whole steps above the starting note: C → D → E → F♯. In the major scale, exactly one tritone exists — between the 4th and 7th scale degrees (F and B in C major).
The acoustic character of the tritone sits in a peculiar middle ground — neither obviously consonant like the perfect fifth nor harshly dissonant like the minor second. It projects an unmistakable quality of unease, suspension, and ambiguity — the sense that something should happen next, but not pointing clearly in any direction.
The popular story says the Catholic Church declared the tritone the devil’s interval and banned it outright. This is largely a myth. The phrase diabolus in musica appeared in pedagogical mnemonics used to teach singers to avoid the interval — not in theological condemnations or official Church decrees.
What was actually prohibited was the melodic leap of a tritone in vocal music. This was practical quality control: a tritone leap is genuinely hard to sing accurately a cappella, and an accidental tritone could introduce unwanted harshness into otherwise smooth passages. The prohibition was about craft, not theology.
By the Renaissance, composers had developed sophisticated techniques for incorporating tritones through careful voice-leading and resolution. The “devil’s interval” reputation took on a life of its own centuries later when Black Sabbath opened their debut album with a tritone riff. Modern listeners associate it with menace partly because heavy metal has trained us to hear it that way.
The same interval sounds completely different in other contexts. “Maria” from West Side Story opens with a tritone and sounds romantic and yearning. “The Simpsons” theme opens with a tritone leap and sounds quirky. Blues turnarounds sound bluesy. The interval has no inherent emotional valence — only acoustic properties that context can point in any direction.
In equal temperament, the tritone has a frequency ratio of approximately 1.4142:1 — the square root of 2. Compare this to the frequency ratios of consonant intervals:
When two pitches sound together, our auditory system processes the frequency relationship. Simple integer ratios produce coincident overtones — their harmonic series overlap at regular intervals, and the intervals blend. The tritone’s √2 ratio is uniquely irrational — it is the only interval in equal temperament whose frequency ratio is algebraically irrational.
The tritone’s overtones cluster near each other without exactly matching, producing acoustic beating — the perceptual signature of the interval: not harsh dissonance, but subtle suspended unease. Additionally, the perfect symmetry means no inherent direction — C-F♯ could resolve down to an F-based harmony or up to a G-based harmony with equal acoustic plausibility. This directionlessness is why the tritone creates powerful tension in functional harmony: the surrounding chord can point it anywhere.
Why the Tritone Sounds Unstable
Compare overtone alignment for perfect intervals vs the tritone. Acoustic comparison visualizer.
F-to-B is an augmented fourth: four letter-positions apart, but one semitone wider than a perfect fourth. B-to-F is a diminished fifth: five letter-positions apart, but one semitone smaller than a perfect fifth. Both span exactly 6 semitones — the same sound, two different spellings.
Why does spelling matter? It communicates voice-leading function. In G7 (G-B-D-F), the tritone is spelled B-F — a diminished fifth. B is the third of the chord (the leading tone in C major) and resolves upward to C. F is the seventh and resolves downward to E. The diminished fifth contracts inward on resolution.
An augmented fourth typically behaves differently — it expands outward. F resolving to E (downward) and B resolving to C (upward) gives outward expansion to the minor sixth E-C. Composers use spelling to communicate direction. In chord charts and lead sheets, the distinction matters less; in classical notation, the spelling carries information about what comes next. The generic term “tritone” covers both spellings without specifying direction.
Every dominant 7th chord contains a tritone between its third and seventh — and that tritone is the acoustic engine of the V-I cadence, the most fundamental resolution in Western tonal music.
In C major, the dominant 7th chord is G7: G-B-D-F. The tritone lies between B (the third, which is also the leading tone — the 7th scale degree) and F (the fourth scale degree, serving as the 7th of the chord). When G7 resolves to C major:
The leading tone (B) moves up by half-step to the tonic (C). Classic leading-tone resolution.
The seventh (F) moves down by half-step to the third of the tonic chord (E). Seventh resolution.
B-F (diminished fifth, 6 semitones) contracts inward to C-E (major third, 4 semitones). The tritone resolves.
Without the tritone, G major (G-B-D) can resolve to C major but the pull feels gentler and less inevitable. The added F — creating the tritone with B — transforms gentle suggestion into harmonic urgency. The leading tone (B) sits one half-step below tonic. The seventh (F) sits one half-step above the third of the tonic chord (E). Both pull strongly toward stable notes. Together they create combined tension that virtually demands resolution.
Every dominant 7th chord is a coiled spring whose stored energy is the tritone’s directional pull.
Watch the Tritone Resolve
Animated voice-leading from V7 to I. Watch the tritone contract inward.
Tritone substitution is one of the most powerful reharmonization tools in jazz — and it flows directly from the properties we’ve just described.
The tritone B-F lives inside G7, where B is the third and F is the seventh. That same tritone B-F also lives inside D♭7 — except now the roles are reversed: F is the third of D♭7, and B (spelled enharmonically as C♭) is the seventh. Both chords contain the same tritone. Because the tritone creates the resolution pull, both G7 and D♭7 can resolve to C major.
Replace G7 with D♭7: instead of the progression G7 → Cmaj7, play D♭7 → Cmaj7. The bass line becomes D♭ → C (descending half-step) instead of G → C (ascending fourth). The chromatic bass movement is smoother and more colorful — a staple of jazz vocabulary.
In practice, tritone substitution chromaticizes the classic ii-V-I progression: Dm7 → G7 → Cmaj7 becomes Dm7 → D♭7 → Cmaj7. The bass line D → D♭ → C descends by half-steps — a seductive chromatic resolution. Reharmonizers apply this constantly. Every dominant 7th chord has a “twin” a tritone away — they share the same tritone, the rest differs, and both can resolve to the same destination.
The tritone permeates modern music in ways that most listeners never consciously notice.
Blues: The tritone is a characteristic interval throughout blues. Every dominant 7th chord in a 12-bar blues contains a tritone. The blues scale’s “blue note” (the ♭5) produces a tritone with the root, giving the scale its characteristically bittersweet ambiguity.
Rock and metal: Black Sabbath’s self-titled track opens with a G-D♭ tritone riff — one of the most famous moments in rock history. Power chord progressions that move a tritone apart became a signature of heavy metal.
Film and TV scoring: The Simpsons theme opens with a tritone leap (C to F♯) — quirky and off-kilter by design. Bernard Herrmann built an entire psychological horror language around tritones in his Vertigo score. The interval signals unease without full resolution — perfect for suspense.
The context paradox: “Maria” from West Side Story uses a tritone to sound romantic and yearning. Blues turnarounds use it to sound gritty and soulful. Jazz substitutions use it to sound sophisticated. Game music uses it for boss battles. The same six semitones sounds completely different depending on context — the interval has no inherent emotional meaning, only acoustic properties that context colors.
Hear the Tritone in Different Genres
Same six-semitone interval. Different musical contexts. Same interval, completely different character.
“Wants” is the operative word — the tritone’s resolution tendencies are strong but not absolute. Here are the five main patterns:
Two notes a diminished fifth apart move toward each other by half-step, ending up a major third apart. B-F → C-E. This is the pattern behind every standard V7-I cadence in major keys. The most common tritone resolution in tonal music.
Two notes an augmented fourth apart move outward by half-step, ending up a minor sixth apart. F-B → E-C. Expansive rather than conclusive — common in Renaissance and Baroque counterpoint, and in certain jazz progressions.
Only one of the two tritone notes moves. This happens frequently in jazz reharmonizations with sustained melody notes, and in complex chromatic voice-leading where moving both notes simultaneously would create parallel motion.
The tritone in one dominant chord becomes the tritone of the substitute dominant (with notes exchanging their roles), and resolves to the same destination. The acoustic resolution happens, but through a different chord.
In modal jazz, ambient music, and Lydian mode contexts, the tritone is held as stable harmonic color rather than tension demanding release. Miles Davis’s “So What,” Wayne Shorter’s writing. This requires a clearly established modal context that redefines what’s “stable.”
Visual identification: An augmented fourth spans four letter-names with 6 semitones (F-to-B). A diminished fifth spans five letter-names with 6 semitones (B-to-F). Both look “almost a fourth or fifth, but with an accidental that deviates.” On the keyboard: always 6 half-steps apart, always exactly halfway across the octave.
All 12 tritone pairs:
By ear: The ascending tritone is famously captured by the first two syllables of “Ma-ri” in “Maria” from West Side Story. The Simpsons theme opens with an ascending C to F♯. Black Sabbath’s opening riff descends through a tritone. The perceptual signature is a feeling of suspense or instability — “something should happen next.”
In early ear training, the tritone is often confused with the perfect fourth (one half-step smaller) and the perfect fifth (one half-step larger). The key distinction is the absence of the “settling” quality that perfect intervals have. The perfect fourth and fifth feel stable at rest; the tritone feels like it’s still asking a question.
Tritone Identification Trainer
Hear it. Identify it. Distinguish it from neighboring intervals. Lock in tritone recognition.
The tritone is the most paradoxical interval in Western harmony. Medieval theorists tried to forbid it. Modern composers can’t stop using it. It’s been called the devil’s interval, the engine of tonal motion, the heart of the dominant chord, the secret of jazz substitution, and the signature of metal menace. What unifies all its uses is its acoustic property of directional ambiguity — six semitones, exactly half an octave, is the only interval that can lean any direction the surrounding harmony tells it to lean. Master the tritone — recognize it visually, hear it reliably by ear, understand its role in dominant chords, control its resolution patterns — and you’ve gained access to one of the most powerful compositional tools in Western music.
Interval Mastery Series