The so-called Easterlin paradox helps explain Keynes’s mistake. According to the economist Richard Easterlin, wealth does not correlate to happiness. A higher salary is obviously always desirable, yet once we’ve reached that target it is never enough: We fall victim to a process of habituation of which we are largely unaware. Similarly, as we each set goals for ourselves driven by our current desires, we fail to take into account how our desires change over time and in new circumstances. This explains why economic growth, more than pure wealth, is the key to the functioning of our society: It provides each of us with the hope that we can rise above our present condition, even though this dream remains ever elusive.

Which brings us to the fundamental question: Will economic growth return, and if it doesn’t, what then? Experts are sharply divided. The pessimists, led by the economist Robert Gordon, believe that the potential for economic growth is now much lower than in the last century. The new industrial revolution may have given us the smartphone, but that hardly compares, in his thinking, to the great advances of the 20th century: electricity, the automobile, the airplane, movies, television, antibiotics. On the other hand, optimists like Erik Brynjolfsson and Andrew McAfee tell us in their book “The Second Machine Age” that Moore’s Law is going to allow “the digitization of just about everything.” Already, Google is experimenting with driverless cars, and robots are caring for the elderly in Japan: Another burst of growth appears to be at hand.

To decide who is right, one must first recognize that the two camps aren’t focusing on the same things: For the pessimists, it’s the consumer who counts; for the optimists, it’s the machines. Yes, computers have in some cases replaced humans, but the essential question then becomes: What happens to the workers who are replaced by machines? This is not a clash between those who believe in technology and those who don’t. New technologies are destined to produce marvels. What matters is whether they will substitute for human labor or whether they will complement it, allowing us to be even more productive.

It’s useful to compare this situation with the 20th century when American farmers, comprising 38 percent of the labor force in 1900, moved to the cities and became highly productive workers in new industries. Economic growth quickly doubled. The fact that the purchasing power of the American middle class has grown so little over the last 30 years reflects another major change: Workers have left the factories — but their productivity in their new jobs (if they find them) is stagnant, meaning that economic growth is petering out. The logical conclusion, then, is that both sides in this debate are right: We’re living an industrial revolution without economic growth. Powerful software is doing the work of humans, but the humans thus replaced are unable to find productive jobs.

So how do we deal with a world without economic growth — if that were to come to pass? How do we motivate people if we can’t fulfill their hopes for rising living standards? One recalls the radical move by Henry Ford to double salaries in his factories to cut back on absenteeism and to reinvigorate his employees’ desire to work. In growing economies you can reward diligent workers with rising wages. Today’s companies do give bonuses to workers based on merit, but that carrot comes with a stick: layoffs if goals aren’t met.