What causes inflation?

Money, first

Inflation is a general rise in prices across an economy. A one-month jump in gasoline is a change in relative prices. Inflation that lasts — the kind that shows up in the twelve-month CPI year after year — is a monetary phenomenon: it is produced only by the quantity of money growing faster than the goods and services that money buys.

Milton Friedman stated the claim in 1970, and he qualified it so it could not be waved away as a slogan:

Inflation is always and everywhere a monetary phenomenon in the sense that it is and can be produced only by a more rapid increase in the quantity of money than in output.

That is the center of this page, not a footnote. Demand, a harvest failure and what people expect next all show up in the month-to-month path. None of them prints the extra money. The institution that does is the Federal Reserve — sometimes alongside a Treasury that finances spending by creating money rather than by taxing or borrowing from the public.

How money gets loose

Three policy choices enlarge the quantity of money, or keep it growing after it already has.

Fiscal expansion financed by money creation. A deficit paid for by taxes or by borrowing from the public rearranges who spends. The same deficit paid for by printing currency or creating bank deposits raises the quantity of money. Friedman drew that line in the same lecture: government spending “clearly will be inflationary if it is financed by creating money”; financed the other way, “by itself, it is not important for inflation.”

Rate suppression. Holding the federal funds rate below the level that would restrain credit is an invitation to more borrowing. More borrowing, in a banking system that creates deposits, is more money.

Balance-sheet expansion. When the Fed buys Treasuries and other assets in size — quantitative easing — it pays by creating reserves. That is money creation. Whether those reserves sit parked or finance spending later, the central bank chose the size of the balance sheet.

None of these is a weather report. Each is a decision with a medium-run consequence for the price level.

Who pays

A rising price level is a transfer. Households on fixed incomes, retirees, and anyone holding cash or a bond that does not reprice lose purchasing power. Wages and some benefits catch up only after the fact, and not always in full. That is how inflation taxes people who saved in the currency.

The twelve-month CPI on this page is the household measure of that tax. The inflation rate page carries the current figure with its “as of” date.

What a supply shock can and cannot do

Oil, a failed harvest, a shipping disruption, a tariff or a war can raise the price of particular goods — and, because energy and food enter so many other costs, can lift the headline price level for a time.

That is a change in relative prices. It is not, by itself, years of broad inflation. If the quantity of money is held, spending reallocates and the one-time rise fades. If the central bank keeps money easy so the shock does not have to be absorbed — the phrase in the coverage is “look through” — it has chosen to validate a higher path for prices.

Raising rates does not drill oil. That is true. It is also not an argument that the Fed is helpless. Looking through a shock is a decision about money over the following year or two. When inflation stays broad after the shock has passed, that decision is part of the cause.

The tell is persistence and breadth. A concentrated spike that fades is a relative-price event. A rise that spreads and stays is monetary. The Fed watches core inflation — the measure excluding food and energy — because a rise that remains after those categories are stripped is more likely to be broad. Food and energy still matter to households; stripping them is a diagnostic, not a dismissal.

Expectations are a channel

If people expect 5 percent inflation, they write it into wages, prices and contracts, and they get something close to 5 percent. That is real. It is not a cause that floats free of money.

They expect 5 percent because they have already watched money stay loose. A publicly stated 2 percent target coordinates other people’s plans only when the promise about future money has been kept. When it has not, “unanchored expectations” is a description of the damage, not a substitute for tightening money.

This is why recovering a currency’s credibility has historically been costly. The cost is the real adjustment after money has already been too easy for too long. The dual mandate does not change the arithmetic: stable prices still require that money not outrun output.

How to read the coverage

• “Inflation is caused by X” — if X is not money, ask whether money accommodated it, and whether the rise is still going after X has passed.
• “The Fed is looking through a supply shock” — that is a decision to leave money easy. If inflation stays broad, that decision belongs in the account.
• “Wages are causing inflation” — wages are a price. Across the economy they rise with the money that pays them. Wages rising with productivity are not a general rise in prices.
• “Inflation is falling” — prices are still rising, more slowly. See the glossary term for that distinction, which is the one most commonly muddled.