And so the focus of policy seems as if it should be less on creating more jobs and more on trying to make the jobs that exist as good as possible, on all dimensions.

For workers, that means higher wages, and the April numbers were actually a bit disappointing on that front. Average hourly earnings for private-sector workers rose only 0.1 percent, and they have been up 2.6 percent over the last year. While there has been some fragmentary evidence that employers are starting to raise wages because of the tight labor market, it isn’t yet clear that there is some overwhelming trend toward workers fully sharing the benefits of an improving economy.

The low unemployment rate means that the still-depressed levels of participation in the work force are hard to chalk up to a shortage of jobs.

Only 79.2 percent of Americans 25 to 54 were working in April, unchanged from March. That number was 81.4 percent the last time the unemployment rate was at its current levels in December 2000.

That means that there are still around 2.3 million people in the United States of prime working age who might come back into the labor market if we were to match the standard from 18 years ago. Higher wages would most likely help, but it would also help to understand better the noneconomic reasons those people aren’t working and how these might be overcome.

The reasons seem to include employers being unwilling to hire ex-offenders or people with opioid and other addiction problems — and similar challenges that are beyond the usual economist’s remit. But while “there aren’t any jobs” is still a reality in some pockets of the United States, it is not, on the national level, true any more.

Finally, for Federal Reserve officials and others who shape policy to try to guide the economy, the sub-4 percent jobless rate can serve as a reminder of how little we know with certainty about what the United States economy is capable of.