Irving Fisher

The Fisher equation, named after American economist Irving Fisher, formalizes the relationship between nominal interest rates, real interest rates, and inflation. The formula essentially states that the nominal interest rate is approximately equal to the real interest rate plus the expected rate of inflation. This concept is fundamental to modern monetary policy and finance.

Irving Fisher was a major proponent of the quantity theory of money, arguing that changes in the money supply directly impact the general price level. He developed the equation of exchange (MV = PT) to mathematically illustrate how money velocity and transaction volume relate to prices. His work heavily influenced later monetarist economists like Milton Friedman.

Irving Fisher spent his academic career at Yale University, where he studied and later became a prominent professor. He was not only an economist and statistician but also a prolific inventor, famously patenting an early index card filing system. His diverse background allowed him to bring a highly mathematical approach to economic theory in the early 20th century.

Fisher's Debt-Deflation Theory explains how a cycle of falling asset prices and rising real debt burdens can trigger severe economic depressions. He proposed this theory in 1933 to explain the Great Depression, after he famously lost a fortune predicting a market recovery just before the 1929 crash. The theory highlights the destabilizing role of over-indebtedness and deflation in an economy.