Irving Fisher

Irving Fisher (1867–1947) was an American economist and statistician whose work shaped theories of interest, money, price levels, and index numbers.

Quantity theory of money: A theory linking the money supply and its circulation rate to nominal spending and the price level. Fisher formalized its exchange equation to analyze relationships among money, transactions, and prices.
Fisher equation: An approximate relation stating that the nominal interest rate equals the real rate plus expected inflation. It captures Fisher’s argument that expected price changes enter nominal interest rates.
Fisher ideal index: A price index equal to the geometric mean of the Laspeyres and Paasche indexes. Fisher proposed it as a balanced index that avoids several systematic biases of simpler formulas.
Eugen von Böhm-Bawerk: An Austrian economist known for theories of capital, interest, and the time structure of production. Fisher engaged with earlier capital and interest theories, including Böhm-Bawerk’s account of time and production.
Debt-deflation: A process in which falling prices increase the real value of debts and can intensify economic distress. Fisher’s 1933 analysis made this mechanism a lasting framework for understanding severe downturns.
Equation of exchange: An identity expressing money times its velocity as equal to a price index times transaction volume. Fisher used this equation as the accounting foundation of his monetary theory.
Rate of time preference: The rate at which a person prefers present consumption to otherwise comparable future consumption. Fisher used impatience to explain why people demand compensation for postponing consumption.
Laspeyres price index: A price index that values current prices using quantities from a fixed base period. Fisher’s ideal index combines this base-weighted measure with the Paasche index.
John Bates Clark: An American economist whose theories of marginal productivity and distribution shaped early neoclassical economics. Clark was Fisher’s teacher at Johns Hopkins and influenced his mathematical approach to economics.
Monetarism: An approach to macroeconomics emphasizing the effects of money supply and monetary conditions on economic activity and prices. Fisher’s quantity-theory work supplied foundations later used and challenged by monetarists.

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