(FORTUNE Magazine) – Do you know what caused the Great Depression?

The popular answer is that it was the stock market crash of 1929. That sounds reasonable, and it's the theme of the single best-selling account of those bleak years--John Kenneth Galbraith's The Great Crash: 1929 (first published in 1955 and still in print today). Galbraith treats the crash as a morality play, in which the sins of greed and speculation are punished by the plague of depression. He concludes by enumerating other factors that might have caused or prolonged the depression, but he assigns the leading role to the crash itself.

The answer you'll get from generalist historians is that the cause of the Great Depression is one of the great unsolved mysteries of the 20th century--"a worldwide phenomenon composed of an infinite number of separate but related events," as one recent history put it--and that economists have been unable to provide a coherent explanation.

The economists beg to differ. In fact, "there now prevails a remarkable degree of consensus among specialists about the causes of the Great Depression," according to Stanford's Barry Eichengreen and Peter Temin of the Massachusetts Institute of Technology. "Recent scholarship has resulted in striking agreement on the reasons for the crisis."* The culprit in the modern view was the gold standard.

What happened in the aftermath of the 1929 Crash began as an economic contraction not so different from most. But the world monetary system was still fragile from the resumption of the gold standard after World War I. When output, prices, and savings began sinking in 1929, policymakers--certain they had to keep their currencies tied to gold at all costs--either did nothing or tightened money supplies. The only way to restore economic stability within the constraints of the gold standard was to let prices and wages fall--in the words of U.S. Treasury Secretary Andrew Mellon, to "liquidate labor, liquidate stocks, liquidate the farmers, liquidate real estate ... purge the rottenness out of the system." What they accomplished instead, according to the new consensus, was to transform an ordinary recession into the Great Depression. It took political change to kill the allegiance to gold, and it came slowly--not till 1933 in the U.S.; 1936 in France.

We can learn at least two lessons from this research. One is that a stock market crash today won't necessarily cause a depression (remember how little impact the 1987 crash had on the real economy?). Monetary policymakers now know what not to do. Two: The idea that we should return to a gold standard--embraced by prominent pols like Jack Kemp and wannabe pols like Steve Forbes--is a dangerous one.

*The Gold Standard and the Great Depression, National Bureau of Economic Research.