Riley became the leader of the Minimalist movement with the composition of In C. It was completed in 1964 and is highly performed considering it unique nature. The piece can run anywhere from 45 minutes to 1 hour 45 minutes according to Riley's website. The performing force is also not prescribed. The score is the part for all player, and it does not matter how many people play or what instruments they play.
The piece is built on a pulse of octave C's in the piano. From there, instruments begin playing microsegments of music that are organized chronologically. All players enter at different points, and all players change from one microsegment to the next at different points. The result is an odd conversation where each participant has something to say, but not assert to say it out of the texture. Harmonically, the segments are all fragments centered around diatonic notes of C major, with the exception of a few explorations of a raised fourth and lowered seventh, creating somewhat of a modal feeling rather than a color wash, like a listener might expect.
Compared to Riley's other composition, this is one of several in the same style of microsegments written on a score that is the part for all players.
When I first learned of this piece, I was fascinated with the idea of it. I honestly wanted to play it with people, but unfortunately never got the opportunity to. Having listened to it several times since, I assume that there is a much greater joy to be had as a performer, rather than a listener. It does not take long for the pulse of octave C's to feel like someone is hammering a nail into your head.
Bonds, Mark Evans. A History of Music in Western Culture. 4th ed. Upper Saddle River, NJ: Pearson Prentice-Hall, 2013.
Domain of Terry Riley. Official website. Accessed May 2, 2014. http://terryriley.net