It's been used by composers and musicians from JS Bach to Jimi Hendrix. It creates an atmosphere of tension, drama and mystery. It's one of the most intriguing elements in the musical universe. But what exactly is the tritone? Read on as we dissect the so-called 'devil in music'.
What is a tritone?
The tritone is a musical interval spanning three whole tones (hence the name). In Western music, the tritone is one of the most distinctive and tension-filled intervals, often associated with dissonance and instability. Its unique, eerie sound has made it a subject of fascination for theorists, performers and composers for centuries.
Once feared for its unsettling sound, the tritone was often avoided in Medieval religious music.
Let's get technical
A tritone is exactly half an octave, consisting of six half steps. For example, in the key of C major, the tritone would be the interval between C and F sharp (or G flat).
The tritone can also be called an augmented fourth (A4) or diminished fifth (d5), depending on its context in harmony. The sound this creates is often described as unsettling, ambiguous, or even eerie due to its tension and tendency to resolve. It crops up a lot during Camille Saint-Saëns's famous Danse Macabre, adding to the ghostly, haunting soundwolrd of that piece:
The tritone naturally resolves to consonant intervals like the major third or perfect fifth, making it a key feature of dominant chords in tonal music. It occurs naturally in the Locrian and Lydian modes, as well as the diminished scale.
The tritone in history
In Medieval times, the tritone was given the nickname diabolus in musica (or, 'the devil in music'). Some accounts persist that the interval was actually banned altogether from church music. If so, this was probably due more to that unsettling sound - that harmonic instability - than to any genuine belief that this was the devil manifesting homself in music.
Even so, throughout the Baroque and Classical eras, composers tended to use the tritone fairly sparingly, and when they did it was as a means of creating tension that resolves to a more stable interval.
Which composers used the tritone?
A variety of composers have deployed the tritone in music. For instance, the 'devil in music' is a central feature of many complex fugues and chorales in the music of Bach, where it serves to build tension. Elsewhere, Beethoven employs the tritone prominently in his Piano Sonata No. 21, the Waldstein, where it creates moments of high drama. And in his opera Fidelio, the villain Don Pizarro gets a leitmotif built around a tritone to emphasise his dark character.
Debussy begins his iconic Prélude à l'après-midi d'un faune with a descending tritone, part of that memorable flute solo. Here, the tritone creates an otherworldly representation of the hypnotic music of a faun's pan-pipes. It also features in an early Debussy cantata, La Damoiselle élue, a musical setting of the poem by Dante Gabriel Rossetti.
The tritone also features in the so-called Devil's Trill Sonata by Giuseppe Tartini. It forms part of the famous 'Tristan chord' in Richard Wagner's great opera Tristan und Isolde, where its lack of resolution evocatively conjure up the pain of unrequited love.
And it is central to Sibelius's darkest, most haunting and introspective symphony, the Fourth, written at a time (1909-11) when Sibelius was at a low ebb, In 1908, the composer had had a cancerous tumour removed from his throat. We hear the unsettling interval right from the get-go, in that dark opening phrase from the cellos, double basses and bassoons:
Why this unsettling interval is all over West Side Story
It's also prominent across jazz, rock, and contemporary classical music, where its dissonant and edgy quality often adds the required atmosphere of tension and drama. For example, the opening riff of Jimi Hendrix's 'Purple Haze' uses a tritone, as does - somewhat unexpectedly, you might think - the chorus of Tony's 'Maria' from Leonard Bernstein's epoch-making musical West Side Story.
That oh-so-familiar motif 'Maria' tells a whole story within its three notes: the interval between the first two syllables is a tritone, creating a sense of tension and doubt, but this then resolves itself with the final note, a perfect fifth above the opening note. Have a listen from 0:40 below:
In fact, Bernstein makes full use of the tritone during West Side Story, and it really helps create the work's unique mood and atmosphere. It all depends on whether the tritone is resolved (as in 'Maria' above), or left unresolved. A resolved tritone suggests optimism and a bright future for these characters; leaving the tritone unresolved suggests the possibility of danger and violence lurking around the corner.
A great example of the latter is the motif for the Jets, one of the two warring gangs at the heart of the story. In the Jets' motif, that haunting descending tritone is not resolved. Instead, it just hangs there, creating dissonance and unease. Have a listen below - it first crops up at around 0:12 ('You're never alone'):
