『The General Theory of Employment, Interest and Money』要約

John Maynard Keynes published The General Theory of Employment, Interest and Money in 1936, and it remains the foundational text of modern macroeconomics. Writing against the classical orthodoxy of his day, Keynes argued that economies do not automatically self-correct to full employment, and that aggregate demand—not supply alone—determines output and employment levels. The book introduced the concept of effective demand, the level of spending that actually materializes in an economy, and showed that it can settle at an equilibrium below full employment, leaving persistent involuntary unemployment. Keynes built his framework around several distinctive ideas. He rejected the classical assumption that saving and investment automatically equate through the interest rate, instead tying interest to liquidity preference—the demand for money as an asset—and to expectations about the future. He introduced the consumption function, showing that consumption rises with income but less than proportionally, and the multiplier, through which an initial change in investment generates a larger change in national income. His analysis of investment emphasized the marginal efficiency of capital and the volatile role of long-term expectations, which he linked to "animal spirits." He also described the paradox of thrift, wherebyhigher saving can reduce aggregate demand and thus national income. The book's policy implications were radical for their time: governments could and should use fiscal and monetary measures to raise demand and combat depression. Its influence shaped the post-war welfare state, the Bretton Woods institutions, and decades of economic policy, though it also provoked enduring debates with monetarists and new classical economists. It is a demanding, technical work of theory, not a popular tract, but it fundamentally reoriented how governments think about recession and unemployment.