12-Tone Music

In the early 1920s in an effort to think differently about musical composition, Austrian composer Arnold Schönberg set rules for composition so that no one tonality is favored and all the notes are used equally. This composition style is called "12-tone music, also 12-tone technique, dodecaphony, twelve-note serialism, and/or twelve-note composition.

All twelve notes in a chromatic scale are arranged in what’s called a "tone row", where each note is used only once. This tone row is known as the "prime". In addition, there are three transformations of the prime tone row, which follow strict mathematical rules. One transformation is the retrograde, which was simply the prime row in reverse order. Another variation is the inversion, which is like the mirror image of the prime row. Here, the first note is the same as the prime, but after that the notes move by the same interval, but in the opposite direction. For instance, if the second note in the prime row were a major third higher than the first note, the second note in the inversion would be a major third lower. The last transformation is known as the retrograde inversion, and (as the name suggests) it’s the inversion of the retrograde.
Like many experimental techniques, the concept is more interesting than the actual music it produced, but this 12-note music technique was used by many famous 20th century composers like Schönberg, Bartok, and Stravinsky.