Diabolus in Musica


As a young piano student I would occasionally hit an interval that made my conservative piano teacher cringe. The combination of notes is a tritone and at certain times in history was called “the devil’s interval” or “Diabolus in Musica.” It really isn’t all that bad sounding under controlled circumstances and was in frequent use by the Baroque period. By the Romantic period composers would intentionally exploit the discordant properties of the interval. In this post we will look at this combination of notes and note how it was viewed throughout history.


Firstly let me explain exactly what this combination is. A tritone is a combination of two notes played in conjunction with each other and spaced exactly three tones (six half steps) apart. (See diagram below.) When struck together they produce an effect that some people find hair-raising. An experienced musician knows how to mitigate this effect by adding other notes strategically so that the tritone comes across as “seasoning” rather than the primary taste. (Much like a strong tasting garnish such as ginger or blue cheese can be too potent unless eaten with other milder foods.)


The first outright prohibition of this interval came from the medieval music scholar Guido di Arezzo. He invented a tonal system based on a hexachord (a six note scale) F-G-A-Bb-C-D. The B was altered to Bb to avoid the tritone between F and B. Guido rejected this interval purely on a theoretical basis. From this point onward (and probably earlier even though we don’t have sources) the tritone was shunned as unstable.

Guido Di Arezzo

Guido Di Arezzo


The 17th and 18th centuries were periods in which great treatises were being written on music theory. Because of the medieval prohibition on the tritone many theorists speculated that the prohibition came from superstition rather than theory. By the early 18th century the term Dabolus in Musica (the Devil in Music) was being applied to the tritone interval. The fact that the interval contained six half-steps (the devil’s number is 666) was convenient to propagate the negative reputation of the tritone.


Someone once told me (maybe a music teacher) that if you were a composer living in the old days (and by old days he or she presumably meant the era when Bach, Beethoven, and Mozart were active) you could be burned at the stake for writing a tritone into your music. There are of course no records of anyone ever being burned at the stake for this reason. This appears to be a myth associated with the ominous interval.

Bb!! It was supposed to be a B FLAT!!!

Bb!! I meant B FLAT!!!

Many composers since the 19th century have exploited the creepy reputation of the interval. Some simply wish to defy conventional composition but others wish to use the interval as a tool to craft a sinister atmosphere. This is seen poignantly in the Danse Macabre by Camille Saint-Saens. This Symphonic Poem begins with the clock striking midnight followed by death playing a discordant sequence on his violin. This sequence begins on a tritone. (Listen to the example below.)


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