Running the entire course of the 20th century, Michael Tippett’s life (1905–1998) was devoted to innovation. He was an English composer who worked within established forms —symphonies, oratorios, string quartets, piano sonatas — to startlingly new effect. But his innovation was not just as a composer. He was also a political and social radical, embedded in Trotskyite, pacifist and gay rights ideas.