Monetary Theory and Policy: Demand, Multiplier, and Transmission
Money demand
Quantity theory: MV = PY. If velocity is stable, money growth determines nominal GDP and, in the long run, inflation. The Cambridge form is Md = kPY. Keynesian liquidity preference says money demand depends on income and interest through transactions, precautionary, and speculative motives. Baumol–Tobin shows transactions demand rises with income but falls with the interest rate, since holding cash has an opportunity cost. Friedman treated money as one asset among many and argued velocity was stable enough to support a money-growth rule.
Money supply and the multiplier
The simple deposit multiplier is 1/rr, but currency drains and excess reserves shrink the realized expansion. In practice M = m × MB, where MB is the monetary base (currency plus reserves) and m reflects the currency ratio, required reserve ratio, and excess reserve ratio. The Fed controls the base, not deposits directly.
Transmission and policy debates
Channels include interest rate, credit, asset price, exchange rate, and expectations. Policy affects output and employment in the short run and prices in the long run; long-run neutrality means real variables are unaffected by money growth. In a liquidity trap near zero rates, added reserves sit idle, so stimulus works through asset purchases and forward guidance. The Phillips curve shows a short-run inflation–unemployment trade-off; the expectations-augmented version denies any permanent trade-off. Rules versus discretion: the Taylor rule links the policy rate to the inflation gap and output gap, and time-inconsistency arguments favor commitment.
Worked example
With rr = 10%, no currency drain, and no excess reserves, a $1,000 open market purchase supports at most 1,000 × (1/0.10) = $10,000 in deposits. Because the public holds some currency, the actual expansion is smaller - that leak is exactly what the simple multiplier ignores.
Traps
Treating the multiplier as an exact prediction; claiming the Fed sets the money supply rather than the base; asserting a permanent inflation–unemployment trade-off; confusing nominal and real rates in the transmission story.