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.
Causes of the Great Depression
From the point of view of today's mainstream schools of economic thought, government should strive to keep some broad nominal aggregate on a stable growth path (for proponents of new classical macroeconomics and monetarism, the measure is the nominal money supply; for Keynesian economists it is the nominal aggregate demand itself). During a depression the central bank should pour liquidity into the banking system and the government should cut taxes and accelerate spending in order to keep the nominal money stock and total nominal demand from collapsing.