PETER S. GOODMAN ESSAY

Experts have long assured us that economic life is governed by the business cycle, a repeating loop of downturn followed by expansion, as reliable as the seasons.

But just as climate change has altered how we contemplate the seasons, some economists argue that the business cycle no longer operates as it once did, failing to replenish the jobs it destroys, and leaving our economy vulnerable to a potentially long-term shortage of work.

The tools we use to assess the business cycle date back to the 1920s, when the economy looked much different. In America, manufacturing jobs have declined sharply as a percentage of overall employment, while services have emerged as the primary economic engine. Automation and globalization have supplied thrifty corporate managers with myriad ways to boost production without hiring.

“It’s a change in the structure of the business cycle,” argues Allen Sinai, chief global economist at the research firm Decision Economics . “There appears to be a new tendency to substitute against labor. It’s permanent, as long as there are alternatives like outsourcing and robotics.”

Certainly, those inclined to argue that commercial life has been remade are frequently chastened when - as often happens - the dusty old laws of economics reassert themselves.

The latest reassessment of the business cycle now has a couple of decades of data to consider. After recession gave way to expansion in March 1991, it took a year before hiring resumed in earnest - a so-called jobless recovery. After the following recession ended in March 2001, two years passed before jobs grew. Many economists assume that the third straight jobless recovery has already begun .

This is not how things are supposed to go, not according to our traditional view of the business cycle. When the economy is growing, businesses hire aggressively as they increase production and sell more goods. As workers spend their paychecks, they distribute dollars throughout the economy, creating business opportunities that prompt other companies to hire - a virtuous cycle. As growth slows, companies let people go, then hire anew when new opportunities emerge.

But as Mr. Sinai and his colleagues see things, our view of the business cycle is antiquated. They say it dates to a time when manufacturing employed roughly one-third of the American workforce, well before what we now call the global economy.

In the middle of the last century, a retailer in Chicago who needed goods likely had to place an order with a factory in the Midwest. Today, that retailer could well send its orders to workers in China and elsewhere. The overall trend appears to make many American companies less inclined to hire .

But labor-oriented economists like Lawrence Mishel at the Economic Policy Institute in Washington argue that the business cycle works the same as it always did; the problem is that economic growth has been weak in recent times. “When growth comes back,” Mr. Mishel said, “so will jobs.”

Kenneth S. Rogoff, a Harvard economist , believes that the lingering dysfunction of the financial crisis will give way to a more healthy flow of money that is not based on excessively low interest rates to spur economic activity. More businesses will borrow and expand and unemployment will settle.