Statistics agencies measure inflation with a consumer price index (CPI), which tracks the changing cost of a representative basket of goods and services people actually buy, food, rent, energy, transport, and reports the percentage change over time. CPI is an observed outcome, not a cause; it tells you that prices rose, but not why.
Explaining why prices rise usually points to some combination of demand-pull pressure (more money chasing a similar quantity of goods), cost-push pressure (rising input costs like energy or wages passed on to consumers), and changes in the quantity of money and credit in the economy. Monetarist economists, following work associated with Milton Friedman, emphasised that persistent, sustained inflation over the long run is closely linked to growth in the money supply outpacing growth in real output.
Central banks track several money supply measures, narrow aggregates like the physical currency and reserves (the monetary base), and broader aggregates like M2 that include most bank deposits, because 'how much money exists' is not one simple number, and different aggregates behave differently during recessions, expansions and periods of unconventional policy like large-scale asset purchases.
Explain more simply
Inflation means prices going up on average, so each unit of money buys a little less than before. A coffee that cost one euro years ago often costs more today.
One important cause is simple: if the amount of money in an economy grows faster than the amount of goods and services for sale, each unit of money tends to buy less over time.
Real-world analogy
Think of the economy as a pizza and money as the number of slices claimed against it. Cutting more slices does not make more pizza; it just makes each slice smaller.
Key facts
- CPI measures the price of a basket of goods over time; it is an outcome, not a cause of inflation.
- Sustained long-run inflation is closely associated with money supply growth outpacing real output growth.
- Central banks track multiple money supply aggregates (such as the monetary base and M2), because 'money' spans a spectrum of liquidity.
Common misconception
“Printing money always causes an immediate, proportional rise in consumer prices.”
The link between money supply growth and CPI inflation involves lags and depends on velocity and where new money flows. New money can inflate asset prices rather than consumer prices for extended periods before, or instead of, showing up in the CPI basket.[1]
Go deeper
The relationship between money supply growth and price inflation is not mechanical or instantaneous, there are variable time lags, and the effect depends heavily on 'velocity' (how quickly money changes hands) and on whether new money flows into goods and services prices or into asset prices like stocks and housing, which CPI baskets often exclude or underweight. This is part of why economists still debate exactly how much of any given inflation episode to attribute to monetary expansion versus supply shocks, wage dynamics or expectations.
It is also worth separating two distinct phenomena: the ongoing, gradual erosion of purchasing power that most fiat currencies experience over decades, and acute hyperinflation episodes, which historically have been driven by extreme, rapid expansion of the money supply, typically to finance government spending when other financing options were exhausted.
Quick check
Answer every question correctly (100%) to complete this lesson.
1.What does the Consumer Price Index (CPI) actually measure?
2.According to monetarist economists, sustained long-run inflation is closely linked to what?
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Extra exam questions
Every question here counts towards your accuracy, XP and rank. No guessing: every answer is explained.
Quick check
Answer every question correctly (100%) to complete this lesson.
1.In monetary terms, what does 'inflation' most precisely refer to?
2.If the money supply grows faster than the production of goods and services, what tends to happen to prices?
3.What is 'purchasing power' in the context of inflation?
4.Which of the following is a common tool central banks use that can influence the money supply?
5.What is commonly meant by 'quantitative easing'?
6.Why can persistent inflation act like a hidden tax on savers?
7.What is the difference between the Consumer Price Index (CPI) and the actual increase in money supply?
8.Historically, what has been a common outcome when governments print large amounts of new currency to fund spending?
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Sources
- Bitcoin: A Peer-to-Peer Electronic Cash System (2008), Satoshi Nakamoto
The original nine-page proposal. Describes proof of work, timestamping and the incentive model.