Question: What is a key reason that scholars and economists want to identify causes of the Great Depression?
About the article "Great Depression", section "Causes".

Candidate passages:
There were multiple causes for the first downturn in 1929.
These include the structural weaknesses and specific events that turned it into a major depression and the manner in which the downturn spread from country to country.
In relation to the 1929 downturn, historians emphasize structural factors like major bank failures and the stock market crash.
In contrast, monetarist economists (such as Barry Eichengreen, Milton Friedman and Peter Temin) point to monetary factors such as actions by the US Federal Reserve that contracted the money supply, as well as Britain's decision to return to the gold standard at pre–World War I parities (US$4.86:£1).
Recessions and business cycles are thought to be a normal part of living in a world of inexact balances between supply and demand.
What turns a normal recession or 'ordinary' business cycle into a depression is a subject of much debate and concern.
Scholars have not agreed on the exact causes and their relative importance.
The search for causes is closely connected to the issue of avoiding future depressions.
A related question is whether the Great Depression was primarily a failure on the part of free markets or a failure of government efforts to regulate interest rates, curtail widespread bank failures, and control the money supply.
Current theories may be broadly classified into two main points of view and several heterodox points of view.
There are demand-driven theories, most importantly Keynesian economics, but also including those who point to the breakdown of international trade, and Institutional economists who point to underconsumption and over-investment (causing an economic bubble), malfeasance by bankers and industrialists, or incompetence by government officials.
The consensus among demand-driven theories is that a large-scale loss of confidence led to a sudden reduction in consumption and investment spending.
Once panic and deflation set in, many people believed they could avoid further losses by keeping clear of the markets.
Holding money became profitable as prices dropped lower and a given amount of money bought ever more goods, exacerbating the drop in demand.
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.
There are also various heterodox theories that downplay or reject the explanations of the Keynesians and monetarists.
For example, some new classical macroeconomists have argued that various labor market policies imposed at the start caused the length and severity of the Great Depression.
The Austrian school of economics focuses on the macroeconomic effects of money supply, and how central banking decisions can lead to over-investment (economic bubble).
General theoretical explanations.
Mainstream theories.
Economist John Maynard Keynes in 1936 argued that there are many reasons why the self-correcting mechanisms that many economists claimed should work during a downturn might not work.
In his book "The General Theory of Employment, Interest and Money", Keynes introduced concepts that were intended to help explain the Great Depression.
One argument for a non-interventionist policy during a recession was that if consumption fell due to savings, the savings would cause the rate of interest to fall.
According to the classical economists, lower interest rates would lead to increased investment spending and demand would remain constant.
However, Keynes argues that there are good reasons why investment does not necessarily increase in response to a fall in the interest rate.
Businesses make investments based on expectations of profit.
Therefore, if a fall in consumption appears to be long-term, businesses analyzing trends will lower expectations of future sales.
Therefore, the last thing they are interested in doing is investing in increasing future production, even if lower interest rates make capital inexpensive.
In that case, the economy can be thrown into a general slump due to a decline in consumption.
According to Keynes, this self-reinforcing dynamic is what occurred to an extreme degree during the Depression, where bankruptcies were common and investment, which requires a degree of optimism, was very unlikely to occur.
This view is often characterized by economists as being in opposition to Say's Law.
The idea that reduced capital investment was a cause of the depression is a central theme in Secular stagnation theory.
Keynes argued that if the national government spent more money to recover the money spent by consumers and business firms, unemployment rates would fall.
The solution was for the Federal Reserve System to “create new money for the national government to borrow and spend” and to cut taxes rather than raising them, in order for consumers to spend more, and other beneficial factors.
Hoover chose to do the opposite of what Keynes sought to be the solution and allowed the federal government to raise taxes exceedingly to reduce the budget shortage brought upon by the depression.
Keynes proclaimed that more workers could be employed by decreasing interest rates, encouraging firms to borrow more money and make more products.
Employment would prevent the government from having to spend any more money by increasing the amount at which consumers would spend.
Keynes’ theory was then confirmed by the length of the Great Depression within the United States and the constant unemployment rate.
Employment rates began to rise in preparation for World War II by increasing government spending.
“In light of these developments, the Keynesian explanation of the Great Depression was increasingly accepted by economists, historians, and politicians”. 
  Ben S. Bernanke.
"Essays on the Great Depression" (2000)  Bernstein, Michael A.
"The Great Depression: Delayed Recovery and Economic Change in America, 1929–1939" (1989) focus on low-growth and high-growth industries  Bordo, Michael D., Claudia Goldin, and Eugene N. White, eds.
"The Defining Moment: The Great Depression and the American Economy in the Twentieth Century" (1998).
Advanced economic history.
Chandler, Lester.
"America's Greatest Depression" (1970).
economic history overview.
De Long, Bradford.
"Liquidation Cycles and the Great Depression" (1991)  Jensen, Richard J.
"The Causes and Cures of Unemployment in the Great Depression," "Journal of Interdisciplinary History" 19 (1989) 553–83.
online at JSTOR in most academic libraries  McElvaine, Robert S. "The Great Depression" (2nd ed 1993) social history  Mitchell, Broadus.
"Depression Decade: From New Era through New Deal, 1929–1941" (1964), standard economic history overview.
Parker, Randall E. "Reflections on the Great Depression" (2002) interviews with 11 leading economists  Salsman, Richard M. “The Cause and Consequences of the Great Depression” in "The Intellectual Activist", ISSN 0730-2355.
Mr. Salsman argues that the Great Depression was "fundamentally" caused by "statist" government policy.
Singleton, Jeff.
"The American Dole: Unemployment Relief and the Welfare State in the Great Depression" (2000)  Warren, Harris Gaylord.
"Herbert Hoover and the Great Depression" (1959).  
Leave-it-alone liquidationism (1929–1933).
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.
The United States government and the Federal Reserve did not do that during the 1929‑32 slide into the Great Depression The existence of "liquidationism" played a key part in motivating public policy decisions not to fight the gathering Great Depression.
An increasingly common view among economic historians is that the adherence of some Federal Reserve policymakers to the liquidationist thesis led to disastrous consequences.
Regarding the policies of President Hoover, economists like Barry Eichengreen and J. Bradford DeLong point out that the Hoover administration’s fiscal policy was guided by liquidationist economists and policy makers, as Hoover tried to keep the federal budget balanced until 1932, when Hoover lost confidence in his Secretary of the Treasury Andrew Mellon and replaced him.
Hoover wrote in his memoirs he did not side with the liquidationists, but took the side of those in his cabinet with "economic responsibility", his Secretary of Commerce Robert P. Lamont and Secretary of Agriculture Arthur M. Hyde, who advised the President to "use the powers of government to cushion the situation".
But at the same time he kept Andrew Mellon as Secretary of the Treasury until February 1932.
It was during 1932 that Hoover began to support more aggressive measures to combat the Depression.
In his memoirs, President Hoover wrote bitterly about members of his Cabinet who had advised inaction during the downslide into the Great Depression:Before the "Keynesian Revolution", such a liquidationist theory was a common position for economists to take and was held and advanced by economists like Friedrich Hayek, Lionel Robbins Joseph Schumpeter, Seymour Harris and others.
According to the liquidationists a depression is good medicine.
The function of a depression is to liquidate failed investments and businesses that have been made obsolete by technological development in order to release factors of production (capital and labor) from unproductive uses.
These can then be redeployed in other sectors of the technologically dynamic economy.
They pointed to the short duration of the Depression of 1920–21 was due to the policy of letting the liquidation occur and argued that the crisis had laid the groundwork for the prosperity of the later 1920s.
They pushed for deflationary policies (which were already executed in 1921) which – in their opinion – would assist the release of capital and labor from unproductive activities to lay the groundwork for a new economic boom.
The liquidationists argued that even if self-adjustment of the economy took mass bankruptcies, then so be it.
Postponing the liquidation process would only magnify the social costs.
Schumpeter wrote that itDespite liquidationist expectations, a large proportion of the capital stock was not redeployed and vanished during the first years of the Great Depression.
According to a study by Olivier Blanchard and Lawrence Summers, the recession caused a drop of net capital accumulation to pre-1924 levels by 1933. 
Some journalists and economists have taken to calling the late-2000s recession the "Great Recession" in allusion to the Great Depression.
The causes of the Great Recession seem similar to the Great Depression, but significant differences exist.
The current chairman of the Federal Reserve, Ben Bernanke, had extensively studied the Great Depression as part of his doctoral work at MIT, and is implementing policies to manipulate the money supply and interest rates in ways that were not done in the 1930s.
Bernanke's policies will undoubtedly be analyzed and scrutinized in the years to come, as economists debate the wisdom of his choices.
Generally speaking, the recovery of the world's financial systems tended to be quicker during the Great Depression of the 1930s as opposed to the late-2000s recession.1928 and 1929 were the times in the 20th century that the wealth gap reached such skewed extremes; half the unemployed had been out of work for over six months, something that was not repeated until the late-2000s recession.
2007 and 2008 eventually saw the world reach new levels of wealth gap inequality that rivalled the years of 1928 and 1929.