The short run had never looked as bleak to Keynes as it did in 1930: “a slump which will take its place in history amongst the most acute ever experienced.” In Britain, the twenties had not so much roared as spluttered. But when Keynes visited Madrid to give a lecture, he chose to adapt one he had been trotting out to students for more than two years, attacking both revolutionary and reactionary doomsayers. Pessimism had made people “blind to what is going on under the surface.”

In the long run we are all dead, but not all at the same time. Keynes’s message was simple: extrapolate conservatively the economic growth rate of the modern age so far, and imagine the wonders one hundred years hence: 2030. His audience would not live to see it, but many of their grandchildren would. The great-grandchildren, born in the last quarter of the twentieth century, would climb a stairway to heaven and bask in unknown pleasures from middle age. The generation after that would be born into paradise.