Considering the legacy of Morton Feldman, the radical American composer who would have turned 90 this year.

Few contemporary composers reach more than a handful of specialist listeners. But – occasionally – a composer’s reputation continues to grow against all odds. The appeal evolves from niche taste to phenomenon, spreading as inexplicably as it does relentlessly. The music of American composer Morton Feldman (1926-1987) is enjoying just such a moment. For confirmation, you need only peruse the discography: since 1989, no less than 249 CDs have included his music. His chamber and solo piano works are performed regularly all over the world. He is widely cited as an influence among composers under 50.

The outpouring of interest has taken many by surprise. During much of his lifetime, Feldman was considered little more than one of John Cage’s hangers-on. His relationship with Cage, a friend and mentor, was a double-edged sword: it gained him access to artistic New York, but few people took him seriously. His compositions were invariably short, and many interpreted this as a lack of substance. Cage’s encouragement of the 24 year-old – Feldman called it Cage’s “permission” – was improbable. But it was also a powerful...