LONDON — Last week, the Green Party proposed giving British workers a new right to a “three-day weekend.” In their pitch, party leaders Caroline Lucas MP and Jonathan Bartley wrote, “How deeply do you dread the long week stretching ahead of you when you go to bed on a Sunday night?”

That makes it sound like a charter for the lazy, which is a shame because the Greens are asking a good question about one of the most important issues in economics right now: Why don’t increases in productivity gain us more free time, and why is British productivity so feeble?

It is not a new question.

• The economist John Maynard Keynes, writing in 1930, believed the future would deliver “three-hour shifts or a fifteen-hour week.”
• In the 1950s, former prime minister Winston Churchill said that he hoped technology would give “the working man what he’s never had – four days’ work and three days’ fun.”
• And in 1994, the French Marxist Andre Gorz wrote a short book, “Farewell to the Working Class,” in which he calculated that by the year 2001 technology could deliver productivity gains that would allow us to work just two days per week, and still get pay rises.

The Green Party is asking the same question anew. The answer: It is possible to create a four-day week with a three-day weekend as a new legal right … but salaried workers should expect to work 10-hour days if that happened.

Seventy years of failure

In the two centuries between the 1800s to the 1940s the working week declined — by law — from at least 120 hours (12 or more hours per day, six days a week) to the current level of about 40 hours per week with two guaranteed days off.

Since then, for the last 70 years, there has been no improvement in working conditions. Some countries — France and Holland — have reduced the working week to nearer 35 hours. But for most full-time employed people, time has stood still: Everyone is tied to their jobs for five days a week, just like our grandparents after World War II.

What went wrong?

In a word, productivity.

Our labour, in terms of GDP growth per hour worked, is simply less effective than it used to be. This chart (below) shows it best. Money invested in work has gets lower returns as time goes by:

Right now, productivity might be negative. It was estimated at -0.1% in 2016, according to The Conference Board.

Lack of productivity is holding the entire UK economy back. We are technically at full employment. That means we can’t simply employ more people to get more growth because there are no more people to employ. To get more growth, we have to make our work more efficient and more productive.

The short answer to that is “yes,” but the long answer explains why employers will be unlikely to reduce the working week. This chart from John Pencavel at Stanford University shows two different measures of worker productivity over a week:

In both measures, your productivity rises the more hours you work. But by about 50 hours a week, the gains are becoming marginal. At 65 hours a week, it’s stalling or going negative. Tired, burned out workers just don’t make any more productive work.

The key is that the sweet spot is somewhere after 40 hours per week.

From an employer’s point of view, if you worked a Green Party week — 32 hours over four days — you are leaving money on the table. Any extra money invested in your work gets increasing returns as you work extra hours.

Employers won’t make much more money from you if you work for six days a week, or 12 hours a day, because you will be doing sloppy, mistake-ridden work. But they will mind a lot if you want to stop working at 20 hours per week, since you’d still be very productive for another 20 after that.

The temptation is to say that employers should just add more workers to fill out those extra hours. But if each of those new workers is also positively productive for 32 hours it merely proves that they’d be even more productive if they all worked 40 or more. Each new worker leaving after 32 hours is money lost.

Time is not money, unfortunately

Capitalism doesn’t work if all its benefits are turned into leisure time. You can’t invest time. It only works if productivity gets turned into money. Employers are willing to pay you to stay, but they won’t pay you to leave. So workers are essentially robbed of the time that their productivity may save them.

Pencavel’s chart also illustrates another problem with capitalism: Humans get tired and become unproductive if they work for too long. That is one reason employers are increasingly replacing workers with robots, who never get tired.

In 1994, Gorz made a startling observation. Capitalism was not, as Marx predicted, creating an ever-larger working class. It was doing the opposite: It was using technology to destroy the working class. Robots were replacing industrial workers. Computers — still a relatively new device in 1994 — were replacing office workers.

Today that same argument is being made, more or less, by Bill Gates. Gates believes robots should be taxed to address the economic destruction they might wreak on jobs.

The Green Party is proposing something essentially different: That workers be paid in the form of both cash and time. When a worker gets paid for five days after working only a four-day week, they will have earned a pay rise in both money and time.

That sounds like a worthy solution. The Economist noted that there have been some small successful experiments with four-day weeks. But it doesn’t alter the employer incentive to push individual workers over the 40-hour barrier. Anyone doing productive work for 32 hours is going to earn their employer even more if they work for 40.

Which is why the Green Party’s idea might work if installed as a law. But only if you accept that your boss will likely want you on the job for four 10-hour days.

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