The ghost of John Maynard Keynes, the father of macroeconomics, has returned to haunt us. With it has come that of his most interesting disciple, Hyman Minsky. We all now know of the “Minsky moment” – the point at which a financial mania turns into panic.

Like all prophets, Keynes offered ambiguous lessons to his followers. Few still believe in the fiscal fine-tuning that his disciples propounded in the decades after the second world war. But nobody believes in the monetary targeting proposed by his celebrated intellectual adversary, Milton Friedman, either. Now, 62 years after Keynes' death, in another era of financial crisis and threatened economic slump, it is easier for us to understand what remains relevant in his teaching.

I see three broad lessons.