ECON30005 · Money and Banking
Inflation: Short-Run Non-Neutrality, Costs and Hyperinflation
Week 3 connects money growth to inflation. It establishes the long-run near-unity correlation between money growth and inflation, uses the OLG intuition to show who is hurt by a surprise money injection (short-run non-neutrality), catalogues the real costs of inflation, and analyses hyperinflation — its fiscal cause, its self-reinforcing dynamics and the collapse of stable velocity. Expect true/false on 'inflation is a monetary phenomenon' and on velocity in hyperinflation, and short essays on the effects of a one-off injection.
What this chapter covers
- 01The long-run money-growth/inflation correlation (McCandless-Weber) and 'inflation is always and everywhere a monetary phenomenon'
- 02Long-run neutrality vs short-run non-neutrality: an unanticipated injection can have real and distributional effects
- 03Who bears an unexpected injection in the OLG model: the current old lose purchasing power (inflation as an implicit tax on money)
- 04Growing money supply M_{t+1} = (1+z)M_t: steady-state inflation equals the money-growth rate z
- 05Quantity-theory decomposition of inflation: Δlog P = Δlog M + Δlog V − Δlog Y
- 06Costs of inflation: distorted pricing, redistribution from debtors to creditors, efficiency loss, uncertainty when volatile
- 07Cost-push vs demand-pull short-run drivers of inflation
- 08Hyperinflation: inflation above 50% per month, caused by fiscal deficits financed by printing money (seigniorage), with velocity rising sharply
Decomposing inflation, and reading a hyperinflation
- +1Set up the decomposition. From MV = PY we have P = MV/Y, so in growth rates Δlog P = Δlog M + Δlog V − Δlog Y. Inflation equals money growth plus velocity growth minus output growth.
- +1Substitute part (a): inflation = 14% + 1% − 3% = 12%. Money growth in excess of output growth (adjusted for the small velocity drift) shows up as inflation.
- +1Part (b): 60% per month exceeds the 50%-per-month threshold, so this is hyperinflation. Its ultimate cause is the fiscal deficit financed by printing money — the revenue from money creation is seigniorage — which feeds a self-reinforcing money-growth/inflation spiral.
- +1Velocity contrast: in hyperinflation people spend money the instant they receive it to avoid the inflation tax, so velocity rises sharply. The stable-velocity assumption behind part (a) breaks down, so a simple decomposition holding velocity fixed would understate the inflation actually experienced.
Key terms
- Short-run non-neutrality
- The result that an unanticipated money injection can move real variables and redistribute wealth, unlike a permanent anticipated change. In the OLG model a surprise injection acts as an implicit inflation tax on the current old's money holdings.
- Inflation tax (seigniorage)
- The real resources a government extracts by printing money: newly created money buys goods while existing money holders lose purchasing power to the resulting inflation. It is the fiscal driver behind sustained high inflation and hyperinflation.
- Steady-state inflation = money growth
- In the OLG model with the money stock growing at a constant rate z (financing wasteful spending), the long-run inflation rate equals z — matching the data fact that sustained inflation requires sustained money growth.
- Quantity-theory decomposition
- The growth-rate identity Δlog P = Δlog M + Δlog V − Δlog Y. In the long run, with velocity stabilising and output at potential, sustained inflation requires money growth outpacing potential-output growth.
- Cost-push vs demand-pull inflation
- Short-run non-monetary drivers: cost-push comes from rising input costs (energy, supply-chain, wages); demand-pull comes from stronger demand (fiscal stimulus, credit growth). Both can raise inflation temporarily without sustained money growth.
- Hyperinflation
- Inflation exceeding 50% per month, ultimately caused by persistent fiscal deficits financed by money creation. Velocity rises sharply, the price system breaks down, and money collapses as a store of value.
Inflation: Short-Run Non-Neutrality, Costs and Hyperinflation FAQ
How can money be neutral in the long run but not the short run?
In the long run a permanent, anticipated money increase scales all prices and leaves real variables unchanged — neutrality. In the short run an unanticipated injection can have real effects because behaviour was set before the surprise: in the OLG model the current old are stuck holding money that now buys less, so they lose while the recipient of the new money gains. Whether output moves depends on who receives the injection — a subsidy to the young raises their capital and temporarily lifts output.
Why does velocity rise in a hyperinflation when the quantity theory assumes it is stable?
The stable-velocity assumption is a long-run approximation for normal times. In a hyperinflation holding money is very costly because it loses value by the hour, so people spend it immediately — each unit of money turns over far more often and velocity spikes. This is why a decomposition that holds velocity fixed understates hyperinflation, and it is a favourite true/false: 'velocity is constant during a hyperinflation' is false.
What is the ultimate cause of hyperinflation?
A fiscal problem, not merely a monetary one. Hyperinflations are triggered by large, persistent government deficits — often from war, a collapse in tax revenue or a loss of borrowing capacity — that the government finances by printing money. The seigniorage revenue comes at the cost of accelerating inflation, and rising inflation expectations feed a self-reinforcing spiral. Stopping it requires fixing the underlying fiscal deficit.
Can AI help me with the inflation material in ECON30005?
Yes. Sia can drill the growth-rate decomposition of inflation, quiz you on the short-run winners and losers of a one-off injection, and test the hyperinflation mechanism and the velocity result. Use it to rehearse the reasoning and check your arithmetic; it does not sit graded quizzes for you, and you should confirm assessment rules on Canvas.
Exam move
Anchor the week on one line — sustained inflation is a monetary phenomenon, but short-run inflation and its distribution are not neutral. Practise the growth-rate decomposition Δlog P = Δlog M + Δlog V − Δlog Y until the signs are automatic, and be able to state the OLG result that steady-state inflation equals the money-growth rate z. For short essays, rehearse the one-off-injection story: who is hurt (the current old, via the inflation tax) and when output moves (a subsidy to the young). Keep a compact list of the costs of inflation and the cost-push/demand-pull distinction. Memorise the hyperinflation essentials — the 50%-per-month threshold, the fiscal-deficit/seigniorage cause, and the sharp rise in velocity — because each is a ready-made true/false. Confirm the exam structure on Canvas.
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