If Mr. Greenspan had acted differently during his tenure as Federal Reserve chairman from 1987 to 2006, many economists say, the current crisis might have been averted or muted.
Over the years, Mr. Greenspan helped enable an ambitious American experiment in letting market forces run free. Now, the nation is confronting the consequences.
Derivatives were created to soften -- or in the argot of Wall Street, "hedge" -- investment losses. For example, some of the contracts protect debt holders against losses on mortgage securities. (Their name comes from the fact that their value "derives" from underlying assets like stocks, bonds and commodities.) Many individuals own a common derivative: the insurance contract on their homes.