•

The policy mistakes of the 1930s stemmed mostly from ignorance. John Maynard Keynes was still a practicing economist in those days, and his central insight about depressions — that governments need to spend when the private sector isn’t — was not widely understood. In the 1932 presidential campaign, Franklin D. Roosevelt vowed to outdo Herbert Hoover by balancing the budget. Much of Europe was also tightening at the time.

If anything, the initial stages of our own recent crisis were more severe than the Great Depression. Global trade, industrial production and stocks all dropped more in 2008-9 than in 1929-30, as a study by Barry Eichengreen and Kevin H. O’Rourke found.

In 2008, though, policy makers in most countries knew to act aggressively. The Federal Reserve and other central banks flooded the world with cheap money. The United States, China, Japan and, to a lesser extent, Europe, increased spending and cut taxes.

It worked. By early last year, within six months of the collapse of Lehman Brothers, economies were starting to recover.

The recovery has continued this year, and it has the potential to create a virtuous cycle. Higher profits and incomes can lead to more spending — and yet higher profits and incomes. Government stimulus, in that case, would no longer be necessary.

An internal memo from White House economists to other senior aides last week noted that policy makers “necessarily tend to focus on the impediments to recovery.” But, the memo argued, the economy’s strengths, like exports and manufacturing, “more than make up for continued areas of weakness, like housing and commercial real estate.”

That optimistic take, however, is more debatable today than it would have been a month or two ago.

As is often the case after a financial crisis, this recovery is turning out to be a choppy one. Companies kept increasing pay and hours last month, for example, but did little new hiring. On Tuesday, the Conference Board reported that consumer confidence fell sharply this month.