For more than 20 years after his death in 1946, the name of John Maynard Keynes achieved a sort of posthumous veneration that mythologised him as not just a great economist but an infallible prophet. This happened on both sides of the Atlantic and across party lines. It was US president Richard Nixon who declared: “We are all Keynesians now.” Well, times change. Myths become vulnerable to debunking – and, if you wait long enough, to rebunking too. The Keynesian era came to grief in the 1970s. For about 30 years Keynes’s reputation languished. Then, in about 30 days, it has apparently been restored.

But the world has moved on since the 1930s when Keynes evolved his most important theories. The dictum, attributed to Keynes, that he changed his mind when the facts changed, has been on the lips of policymakers. There never was a timeless “Keynes” whose every utterance had prophetic force. There was instead a historical Keynes who came up with lots of bright ideas as he confronted different problems.