Today a bit of music theory. The most notorious interval in music is the tritone, the so called “devil in music.” This is the interval of an augmented 4th (that is, for instance, from C to F-sharp). It has all kinds of odd properties both theoretical (unlike other intervals it inverts to itself) and auditory (it seems to shimmer with instability).
Once forbidden in traditional western harmonies, as it tends to undo a solid sense of key, it gained favor as a sort of special effect in the 19th century music, and then became something more serious in 20th century works. (The somber opening of Britten’s War Requiem relies on it.)
It is all over “West Side Story,” which is full of clever musical tricks and references (the serial technique in “Cool” for instance). Perhaps the most subtle of the many tritones in the music (perhaps when all the dust has settled Bernstein’s greatest achievement), is how it weaves in and out of the tune and accompaniment to “Something’s Coming.” Far from being some technical error, it’s evocative, hopeful, and at the same time prophetic. Like a line of poetry that doesn’t quite turn. (It’s also key to how LB sets the word “Maria.”)
Here is “Something’s Coming” from the 60s movie: