Causes of the Great Depression
Second, there are the monetarists, who believe that the Great Depression started as an ordinary recession, but that significant policy mistakes by monetary authorities (especially the Federal Reserve) caused a shrinking of the money supply which greatly exacerbated the economic situation, causing a recession to descend into the Great Depression. Related to this explanation are those who point to debt deflation causing those who borrow to owe ever more in real terms.
Perspectives on capitalism by school of thought
The Chicago School of economics is best known for its free market advocacy and monetarist ideas. According to Friedman and other monetarists, market economies are inherently stable if left to themselves and depressions result only from government intervention.
Friedman argued that the Great Depression was result of a contraction of the money supply controlled by the Federal Reserve and not by the lack of investment as John Maynard Keynes: "There is likely to be a lag between the need for action and government recognition of the need; a further lag between recognition of the need for action and the taking of action; and a still further lag between the action and its effects". Ben Bernanke, former Chairman of the Federal Reserve, is among the economists today generally accepting Friedman's analysis of the causes of the Great Depression.