Three hours a day is quite enough,” wrote John Maynard Keynes in his 1930 essay Economic Possibilities for our Grandchildren. The essay continues to tantalise its readers today, thanks in part to a forecast that is looking magnificently right — that in advanced economies people could be up to eight times better off in 2030 than in 1930 — coupled with a forecast that is looking spectacularly wrong, that we would be working 15-hour weeks.

In 2008, economists Lorenzo Pecchi and Gustavo Piga edited a book in which celebrated economists pondered Keynes’s essay. One contributor, Benjamin Friedman of Harvard University, has recently revisited the question of what Keynes got wrong, and produced a thought-provoking answer.

First, it is worth teasing out the nature and extent of Keynes’s error. He was right to predict that we would be working less. We enter the workforce later, after long and not-always-arduous courses of study. We enjoy longer retirements. The work week itself is getting shorter. In non-agricultural employment in the US, the week was 69 hours in 1830 — the equivalent of working 11 hours a day but only three hours on Sundays. By 1930, a full-time work week was 47 hours; each decade, American workers were working two hours less every week.