The idea of “taking a line for a walk” comes from one of Birtwistle’s favourite artists, Paul Klee. A preoccupation with Klee and his theories was an inspiration for one of the definitive Birtwistle pieces of the late 1970s, Carmen Arcadiae Mechanicae Perpetuum. Using Klee’s idea of the difference between “dividual” and “individual” phenomena – the difference between, say, the endlessly divisible nature of water, as opposed to the singularity, the indivisibility, of a bottle of water – Birtwistle conjured a series of different musical materials. The question was then how to repeat these blocks of material, and how to transform them. On their own, each block is like a little machine of processes and patterns, but nothing ever repeats in quite the way you expect. That’s because Birtwistle used a series of random numbers to help generate how the blocks would recur, how long they would last, and even what notes they would use.

And here’s the paradox. “I didn’t make any decisions in writing Carmen,” Birtwistle says, since so much of the structure was generated through random procedures, “and yet it sounds like me – and no one else could have written it.”