It's Baaack! Japan's Slump and the Return of the Liquidity Trap

In the early years of macroeconomics as a discipline, the liquidity trap-that awkward condition in which monetary policy loses its grip because the nominal interest rate is essentially zero, in which the quantity of money becomes irrelevant because money and bonds are essentially perfect substitutes-played a central role. Hicks (1937), in introducing both the IS-LM model and the liquidity trap, identified the assumption that monetary policy was ineffective, rather than the assumed downward inflexibility of prices, as the central difference between " Mr. Keynes and the classics ". It has often been pointed out that the Alice-in-Wonderland character of early Keynesianism, with its paradoxes of thrift, widow's cruses, and so on, depended on the explicit or implicit assumption of an accommodative monetary policy; it has less often been pointed out that in the late 1930s and early 1940s it seemed quite natural to assume that money was irrelevant at the margin. After all, at the end of the 30s interest rates were hard up against the zero constraint: the average rate on Treasury bills during 1940 was 0.014 percent. Since then, however, the liquidity trap has steadily receded both as a memory and as a subject of economic research. Partly this is because in the generally inflationary decades after World War II nominal interest rates stayed comfortably above zero, and central banks therefore no longer found themselves " pushing on a string ". Also, the experience of the 30s itself was reinterpreted, most notably by Friedman and Schwartz (1963); emphasizing broad aggregates rather than interest rates or monetary base, they argued in effect that the Depression was caused by monetary contraction, that the Fed could have prevented it, and implicitly that even after the great slump a sufficiently aggressive monetary expansion could have reversed it. To the extent that modern