“It takes a heap of Harberger triangles to fill an Okun gap,” wrote James Tobin in 1977, four years before winning the Nobel Prize in economics. He meant that the big issue in economics was not battling against monopolists but preventing recessions and promoting recovery.

After the misery of recent years, nobody can doubt that preventing recessions and promoting recovery would have been a very good idea. But economists should be able to think about more than one thing at once. What if monopoly matters, too?

The Harberger triangle is the loss to society as monopolists raise their prices, and it is named after Arnold Harberger, who 60 years ago discovered that the costs of monopoly were about 0.1 per cent of US gross domestic product – a few billion dollars these days, much less than expected and much less than a recession.