The Quantity Theory
- The quantity theory of money links the money supply to the general price level.
- It builds on Fisher's equation of exchange, which is true by definition.
- The theory then assumes velocity (V) and the volume of transactions (T) are broadly stable.
- On that assumption, a rise in the money supply (M) feeds through mainly to prices (P).
Equation of exchange
M×V=P×T M \times V = P \times T M×V=P×TDefinition
Quantity theory of money: with V and T assumed stable, a change in M causes a proportional change in the price level P.
Equation of exchange (MV = PT): M is the money supply, V the velocity of circulation, P the price level and T the volume of transactions.
Velocity of circulation: the average number of times each unit of money is spent on output in a period.
Key Idea
- The equation of exchange is an identity, true by definition.
- The theory adds the assumption that V and T are stable.
- It gives a monetary explanation of inflation.
How the Theory Works
- The equation says total spending (M × V) equals the money value of output (P × T).
- If V and T are fixed, any rise in M must show up as a higher P.
- So a money supply growing faster than output pushes the price level up.
- This is the monetarist claim that inflation is essentially a monetary phenomenon.
Example
- Suppose M rises by 5% while V and T are unchanged.
- So the price level rises by about 5%, matching the growth in the money supply.
Questioning the Assumptions
- Velocity may not be stable: if households hold more money, V falls and the link weakens.
- When there is spare capacity, extra money can raise real output (T) rather than P.
- If V or T move, the proportional link from M to P breaks down.
- It depends on the time horizon: the link is stronger in the long run than the short run.
Note
- After the 2008 financial crisis, velocity fell as banks and households held more money.
- So quantitative easing did not bring the high inflation some had feared.
- In a deep recession, extra money can raise output instead of prices.
Evaluation
- For the theory: over the long run, high money-supply growth and inflation move closely together. In Zimbabwe around 2008 the central bank printed money to finance a large government deficit while real output was collapsing, so with T falling the surge in M fed almost entirely into P, producing hyperinflation; Venezuela after 2016 followed the same path.
- Against: V and real output are not truly constant, especially in the short run.
- With spare capacity, extra money can lift output first, so prices need not rise in proportion.
- On balance, the setting decides: in high-inflation, long-run cases where the money supply grows far faster than output, as in Zimbabwe, the link is close to one-for-one and the theory is a reliable guide; but in a demand-deficient recession with spare capacity and a falling velocity, as under post-2008 quantitative easing, extra money is largely held or raises output rather than prices, so the proportional result holds only when V and T are stable.
Exam technique
- State the equation M × V = P × T and define each term.
- Question whether V and T are really stable before asserting the result.
- Separate the long-run link from the short-run picture.
Common Mistake
- Do not leap from M to P without checking the assumptions.
- The proportional result needs a stable V and a stable T.
Self review
- State Fisher's equation of exchange.
- What does each term stand for?
- What is the monetarist claim?
- Why might the assumptions fail?
- When can extra money raise output rather than prices?
