Its working population has been declining for years and is expected to fall to 47 million from 54 million by 2039. And it’s not alone in this. Forty-six countries around the world — including major powers like Japan, Russia and China — now have shrinking populations.

Demographics are usually the main driver of economic growth, so it is basically inevitable that these countries will now grow at a much slower pace. And we are not talking about minor population declines. Projections for 2040 show China’s working-age population falling by 114 million, Japan’s by 14 million. With a shrinking labor force, these economies will inevitably slow and, at times, contract. To keep calling two negative quarters in a row a “recession” implies that this outcome is somehow abnormal or unhealthy. That will no longer be the case.

To avoid overreacting, the discussion about economic health needs to shift to measures that better capture satisfaction and contentment, like per capita income growth. In countries with shrinking populations, per capita incomes can continue to grow so long as the economy is shrinking less rapidly than the population. This helps explain why, for example, Japan isn’t facing more social unrest. Its economy has grown much more slowly than that of the United States in this decade, but because the population is shrinking its per capita income has grown just as fast as America’s — around 1.5 percent per year.

Shrinking populations also help explain why unemployment is at or near multi-decade lows, even in countries with serious growth worries, like Germany and Japan. Gainfully employed Germans and Japanese won’t really feel as if their countries are in a slump until per capita G.D.P. growth turns negative — which may prove to be a more useful way to think about recessions in this new era.

The definition of success also needs to change. Many emerging countries still aspire to the double-digit growth rates experienced by what were known as the “Asian miracle economies” from the mid-1960s to the early 1990s, when populations and trade were booming. But no economy had grown so fast before then, and as population and trade surges recede, it’s unlikely any country can repeat those feats.