Fishers quantity theory of money

 Fisher's research into the basic theory of prices and interest rates did not touch directly on the great social issues of the day. On the other hand, his monetary economics did and this grew to be the main focus of Fisher’s mature work.

It was Fisher who (following the pioneering work of Simon Newcomb) formulated the quantity theory of money in terms of the "equation of exchange:" Let M be the total stock of money, P the price level, T the amount of transactions carried out using money, and V the velocity of circulation of money, so that

Later economists replaced T by the real output Y (or Q), usually quantified by the real Gross domestic product (GDP).

Fisher's Appreciation and Interest was an abstract analysis of the behavior of interest rates when the price level is changing. It emphasized the distinction between real and nominal interest rates:

where is the real interest rate, is the nominal interest rate, and the inflation is a measure of the increase in the price level. When inflation is sufficiently low, the real interest rate can be approximated as the nominal interest rate minus the expected inflation rate. The resulting equation is known as the Fisher equation in his honor.

Fisher believed that investors and savers – people in general – were afflicted in varying degrees by "money illusion"; they could not see past the money to the goods the money could buy. In an ideal world, changes in the price level would have no effect on production or employment. In the actual world with money illusion, inflation (and deflation) did serious harm. For more than forty years, Fisher elaborated his vision of the damaging “dance of the dollar” and devised various schemes to “stabilize” money, i.e. to stabilize the price level. He was one of the first to subject macroeconomic data, including the money stock, interest rates, and the price level, to statistical analyses and tests. In the 1920s, he introduced the technique later called distributed lags. In 1973, the Journal of Political Economy posthumously reprinted his 1926 paper on the statistical relation between unemployment and inflation, retitling it as "I discovered the Phillips curve". 

Index numbers played an important role in his monetary theory, and his book The Making of Index Numbers has remained influential down to the present day.

Fisher's main intellectual rival was the Swedish economist Knut Wicksell. Fisher espoused a more succinct explanation of the quantity theory of money, resting it almost exclusively on long run prices. Wicksell's theory was considerably more complicated, beginning with interest rates in a system of changes in the real economy. Although both economists concluded from their theories that at the heart of the business cycle (and economic crisis) was government monetary policy, their disagreement would not be solved in their lifetimes, and indeed, it was inherited by the policy debates between the Keynesians and monetarists beginning a half-century later.

Following the stock market crash of 1929, and in light of the ensuing Great Depression, Fisher developed a theory of economic crises called debt-deflation, which attributed the crises to the bursting of a credit bubble. According to Fisher, the bursting of the credit bubble unleashes a series of effects that have serious negative impact on the real economy:

1. Debt liquidation and distress selling.
2. Contraction of the money supply as bank loans are paid off.
3. A fall in the level of asset prices.
4. A still greater fall in the net worth of businesses, precipitating bankruptcies.
5. A fall in profits.
6. A reduction in output, in trade and in employment.
7. Pessimism and loss of confidence.
8. Hoarding of money.
9. A fall in nominal interest rates and a rise in deflation-adjusted interest rates.