When Marx went into his inner exile in the British Museum, he followed the strategy “One step backward, two steps forward,” taking time off from politics to fashion a tool that could then be of use in politics. The theory he developed has done service for a century but it becoming increasingly irrelevant for most of our urgent problems. “Back to the British Museum!” is hardly a slogan with mass political appeal, but it is one that Marxists would do well to ponder.