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Wharton professor Adam Grant has long advocated for a shorter work week than the 40-hour minimum most professionals have now.

Last week he took that message to the World Economic Forum in Davos, where he shared the stage with Dutch economist and historian Rutger Bregman, author of the book Utopia for Realists. Bregman, who has long advocated for both a universal basic income and a 15-hour work week, said the trend toward fewer working hours that started in the 20th century should continue.

“For decades, all the major economists, philosophers, sociologists, they all believed, up until the 1970s, that we would be working less and less,” he said.

“In the 1920s and 1930s, there were actually major capitalist entrepreneurs who discovered that if you shorten the working week, employees become more productive. Henry Ford, for example, discovered that if he changed the working week from 60 hours to 40 hours, his employees would become more productive, because they were not that tired in their spare time.”

Grant agreed, citing research that found a positive link between employee happiness and productivity.

“I think we have some good experiments showing that if you reduce work hours, people are able to focus their attention more effectively, they end up producing just as much, often with higher quality and creativity, and they are also more loyal to the organizations that are willing to give them the flexibility to care about their lives outside of work,” he said.

Research shows that four-day work weeks definitely make workers happier, and they could even help close the gender pay gap. What isn’t clear, however, is whether they actually make workers more productive. Research at a firm that experimented with a four-day week in New Zealand found that some employees worked harder and more efficiently in the shorter time frame, and some let their output drop along with their work hours.

But the research was clear: workers were happier. And perhaps, Bregman has argued in the past, that may be a more noble goal than mere productivity.