Morton Feldman wrote music that was very quiet, often very long and slow, and in which nothing much ever seemed to happen. He made a career out of whispering, having learned that this is the surest way to make people listen properly to your music. I think it's because he was certain of his audience's attention that he was able to get away with such sparse material.
Christian Wolff in Cambridge from 1963 is a short piece for unaccompanied choir. It's dream logic music: the way he moves from chord to chord makes perfect sense at the time, it's only afterwards that the sequence of events falls apart. It's as if Feldman, like Pauline Oliveros, is telling us that different rules apply for different types of listening.