The devil can cite Scripture for his purpose.William Shakespeare, The Merchant of Venice
A tritone is the interval of three whole tones, six semitones, half an octave: C to F sharp, E to B flat, the distance between the fourth and the seventh notes of any major scale. Named for the three whole steps it spans and spelled either as an augmented fourth or as a diminished fifth depending on which way the harmony means to leave it, the tritone sits inside every major scale, F against B in C major, like a grenade in a coat pocket with the pin already torn out and a thumb pressed hard on the lever, all of the blast held in and none of it spent. The devil, as it turns out, lives in the scale books.
Nobody has to hunt for it. It is there in the white keys.
The French composer who handed Death a fiddle with its top string let down a semitone, from E to E flat, so that its two highest open strings sounded the tritone before a finger touched them, was Camille Saint-Saëns, and his Danse macabre of 1874 opens its midnight with the skeleton tuning up on exactly that interval. The nickname was old by then. The Romantics were the first to cast the devil in the part.
What a tritone is, and where to find it on a guitar
Intervals are counted in semitones, the distance of one fret on a guitar. A perfect fourth is five, a perfect fifth is seven, and the tritone sits alone at six, between the two steadiest intervals in the scale and belonging to neither. On a piano, and on a guitar in equal temperament, its two spellings fall on the same key and the same fret; the spelling only tells a trained reader where the note wants to go next.
| Interval | Semitones | From C | Where it wants to go |
|---|---|---|---|
| Perfect fourth | 5 | C to F | Stable |
| Augmented fourth | 6 | C to F sharp | Outward, to a sixth |
| Diminished fifth | 6 | C to G flat | Inward, to a third |
| Perfect fifth | 7 | C to G | Stable |
That last column is the whole grammar of the interval. Written as an augmented fourth, F up to B, it wants to widen, the F falling to E and the B rising to C, landing on a sixth. Written as a diminished fifth, B up to F, it wants to close, the two notes moving inward onto C and E, a third. Classical harmony built three centuries of cadences on that pull.
Jazz found a second use for the same fact. Because the tritone splits the octave exactly in half, the dominant seventh chords a tritone apart, G7 and D flat 7, share the same tritone, B and F, spelled differently, and a jazz player can swap one for the other in a cadence. Conservatories call it the tritone substitution. The devil, it seems, works on both sides of the bar line.
The ear learns it fastest from tunes it already knows. The opening of the theme to The Simpsons, written by Danny Elfman in 1989, climbs a tritone on its first two notes, and so does "Maria", from Leonard Bernstein's West Side Story of 1957, on the first two syllables of the name. Sing either, stop on the second note, and the unrest is audible at once: the melody cannot stay there and moves up a semitone to the fifth almost before the singer has breathed.
On a guitar the tritone is easy to find. On a single string it is six frets: the open low E against the B flat at the sixth fret. Across two strings it is the power chord grip with the upper finger pulled back one fret, root on the sixth string and the next note one fret higher on the fifth, open E against the B flat at the first fret of the A string. Guitarists call that grip the flat five. How the grip it spoils is built belongs to the power chord, and the move from one to the other takes a single fingertip.
The devil, as it turns out, lives in the scale books.
How the tritone became the devil's interval
The medieval rule against the interval and the Latin tag, diabolus in musica, first found in print in 1702, are traced in the theory chapter. The rule was a teacher's rule about singing. The devil came later, and he came from the opera house and the concert hall of the nineteenth century, where composers wanted a sound for the supernatural and found one already waiting in the textbooks.
The Hungarian pianist who opened his sonata after reading Dante with a sequence of falling tritones in the bass, like a staircase sawn through step by step into the pit, was Franz Liszt, and the piece, published in 1858 in the second book of his Years of Pilgrimage, made the interval the sound of damnation for every pianist who played it. Saint-Saëns gave it to Death sixteen years later. By the twentieth century it was the house key of anything unholy on a stage.
The line into heavy metal runs through an English composer. "Mars, the Bringer of War", the first movement of Gustav Holst's suite The Planets, grinds forward in five beats to the bar over a hammered G, and its brass lay chords a tritone away on top of it. The bassist who liked the piece enough to pick its opening out on his instrument at a rehearsal was Geezer Butler, and by his own account Tony Iommi came in the next day with the riff of the song "Black Sabbath". What Black Sabbath did with that interval is dissected note by note in the chapter. The route to it ran through an orchestra.
The blue note and the flat five
The other road to the interval came from the blues. Add one note to the minor pentatonic scale, the flattened fifth, and it becomes the blues scale: in E, the notes E, G, A, B flat, B and D. That B flat is a passing note, a smear between the fourth and the fifth, set in the scale like a fishhook, barbed so that once the ear has swallowed it the scale cannot be pulled back to its old innocence. Blues players bent through it. Heavy metal stopped and sat on it.
The difference is duration. In a blues solo the flat five lasts a fraction of a beat and resolves upward onto the fifth. In a heavy metal riff it can be struck, held and struck again as a destination in its own right, and that single decision, holding the passing note instead of passing through it, turns a colour of the blues into the foundation of a riff. The interval is the same six semitones. The attitude is not.
The tritone in metal after Black Sabbath
After 1970 the interval stopped being an effect and became a vocabulary. Thrash players of the eighties built chromatic riffs in which the flat five turns up as often as the fifth itself, death metal leaned on it further, and black metal made the tritone and the minor second its two favourite frictions. The chapter shows it under "Enter Sandman" in 1991. By then the anathema of the theory books was a beginner's exercise.
One band finally put the old Latin tag on a record sleeve. The Californian quartet that had spent the better part of two decades answering accusations of devil worship with ever faster riffs was Slayer, and in June 1998, on American Recordings, it called its eighth studio album Diabolus in Musica, nailing the theorists' nickname over its own door like a horseshoe hung upside down, points to the ground, so that every bit of luck in the house runs out. Played mostly in a low C sharp tuning, the record takes its cue from the interval named in its own title.
"Stain of Mind", from that album, shows how far the interval had travelled from Liszt's piano: detuned and palm muted, driven as a groove rather than laid out note by note on a keyboard. Nobody needed a textbook to hear it. Three decades of metal had taught the ear.
Tuning moves where the interval lands without changing what it is. With the low string dropped to D, the flat five sits at the sixth fret of that string, on the note A flat, a sound worth listening for across the songs in drop D.
Six semitones, one fret short of a fifth. The devil has never needed more.
