Perhaps more than any other composer of his generation, Stockhausen realised that serialism had an expressive potential which went far beyond the method of twelve-tone composition devised by Schoenberg. In these three key works works from the 1950s and early 1960s he found ways of using the serial principle to govern not just pitch, but every aspect of sound-types and their distribution in time and space, culminating in Plus-Minus, a score which specified not sounds but rather a system of organising sounds. — Christopher Fox