Macroeconomics: The Economy as One Machine, and Why It Stalls

In June 2022 a US shopper's costs were about 9% higher than a year earlier; in October 2022 the euro area peaked at 10.6%; in Turkey the annual average that year was 72%, and in Argentina in 2024 it was 220%. Meanwhile in Japan prices barely moved for a generation, and in Spain in 2013 more than one worker in four had no job. Same planet, same technology, wildly different experiences. The questions behind them are the ones macroeconomics asks: why does an economy grow, why do prices rise, who gets work, and what, if anything, can a government or a central bank do about it?

A macroeconomics graduate reads those headlines as flows through a few connected pipes: output, prices, jobs, money and debt. The pipes are simple; the arguments over how to turn the taps are not, and this piece tells you who argues what. The data below is real and dated, from several regions. The models in the sliders are textbook toys with invented numbers, labelled as such.

GDP, and what it misses

Gross domestic product is the market value of everything produced inside a country in a year. You can count it three ways that must agree: add up what is produced, what is earned, or what is spent. The spending version is the one students memorise:

GDP is a superb tool for what it was built for: tracking output and jobs through a slump. Simon Kuznets, who built the first US national accounts, wrote in his 1934 report that "the welfare of a nation can scarcely be inferred from a measure of national income". It leaves out unpaid work (cooking, care for your parents), most environmental damage, and how income is shared. It also counts a rebuilt city after a flood as growth. Use it as a gauge of activity, not of well-being. Two standard adjustments matter: real GDP strips out price changes, and per capita divides by people, because a big country is not a rich one.

Growth: compounding and the Solow idea

Modest differences in growth rates, held for decades, make different worlds. Output per person growing at 1.6% a year doubles in 44 years; at 8.1% it doubles in about 9. The rule of thumb is to divide 70 by the percent. The table uses GDP per person, adjusted for price differences between countries, from the World Bank in constant 2021 international dollars.

Country	1990	2024	Times larger	Per year
China	1,667	23,841	14.3	8.1%
India	2,140	9,416	4.4	4.5%
South Korea	14,378	55,071	3.8	4.0%
United States	44,384	75,698	1.7	1.6%
Nigeria	5,424	7,994	1.5	1.2%
Japan	36,138	47,480	1.3	0.8%
Mexico	17,170	21,970	1.3	0.7%

Where does growth come from? The workhorse is the Solow model (Robert Solow, 1956; Nobel Prize 1987). An economy has workers, machines (capital) and technology. Saving builds new machines; machines wear out. But each extra machine adds less than the last, so with a fixed saving rate the economy settles at a level where new investment just replaces wear. Past that point more saving raises the level of income, not its growth. Lasting growth in income per person needs better technology and skills. Poor countries starting with little capital can grow fast by catching up, which is part of why China and India grew faster than the US.

With 20% saving and 1% technology growth, output per worker climbs fast at first (year 5 growth is about 3.6%) and then settles to the pace of technology: about 1.1% by year 70, heading for 1%. Raise saving to 40% and the level ends higher, but the long-run growth rate is the same 1%. That is the Solow lesson, and why economists spend so much time on ideas, institutions and schooling. It is a model of mechanics, not a complete theory; Development Economics (34/48) is the argument about what else matters.

Inflation: a basket, not a feeling

Inflation is a sustained rise in the general level of prices. Statistical agencies measure it by pricing a fixed basket of goods a typical household buys (rent, food, fuel, transport) every month and tracking its cost. The weight of each item is its share of spending. Two consequences stay with you: your inflation differs from the headline whenever your basket differs, and the measure shifts when people switch goods.

Real data, from the World Bank (average annual consumer prices, per cent):

Country	2022	2024
Argentina	72.4	219.9
Turkey	72.3	58.5
Nigeria	18.8	33.2
Brazil	9.3	4.4
United States	8.0	2.9
Germany	6.9	2.3
India	6.7	5.0
Japan	2.5	2.7

With energy up 30% the average household's costs rise about 7.2%; the tight-budget renter's rise 8.4% and the retiree's 6.5%, because food and energy take a larger share. Most central banks, from the US to the euro area, aim for about 2% a year, a target chosen as a compromise between the harm of prices rising fast and the risk of falling prices, which make debts heavier and cause people to delay purchases.

Unemployment: a flow, not a stock

You are unemployed in the official sense if you have no job, are available, and have actively looked recently. People who have given up looking or can't find enough hours don't count, which is why statisticians also publish broader measures. The headline rate is the share of the labour force (workers plus job-seekers) out of work.

What a graduate remembers is that it is a pool with a tap and a drain. Each month some employed people lose jobs and some unemployed people find them. If a fraction s of workers lose their jobs monthly and a fraction f of the unemployed find one, the pool settles at a rate of s ÷ (s + f). A rich-country economy can have lots of churn and a low rate, or little churn and a high one.

Place	Rate	Year
Greece	27.7%	2013
Spain	26.1% (11.4% in 2024)	2013
South Africa	32.3%	2024
United States	14.8% (April 2020), 3.4% (April 2023)	monthly
Germany	3.4%	2024
Japan	2.5%	2024

At 1.2% losing and 25% finding, the pool settles at 4.6%. Slow hiring by itself does the damage in a downturn: at 10% finding, the same layoffs give 10.7%. And the average spell is 1 ÷ f months, so a deep slump turns a short hunt into a long one. Economists distinguish frictional (between jobs), structural (skills or location mismatch) and cyclical (too little demand) unemployment, and the policy for each differs.

Money and banks: where deposits come from

Most of the money you hold is a number in a bank account. The old textbook story is the money multiplier: you deposit 100, the bank keeps a fraction as reserves and lends the rest, that loan becomes someone else's deposit, and so on. With a reserve ratio r the deposits can grow until they total the first deposit divided by r.

At 10% a first deposit of 100 supports up to 1,000 of deposits; after 10 rounds you are at about 651. But the Bank of England's 2014 article "Money creation in the modern economy" (McLeay, Radia and Thomas) argues that the textbook story runs backwards: "the majority of money in the modern economy is created by commercial banks making loans", and banks "do not act simply as intermediaries, lending out deposits that savers place with them". A loan creates the matching deposit. What limits lending is then not reserves but borrowers' demand, banks' capital and the central bank's interest rate. That fits the fact that the US Federal Reserve set reserve requirements to zero in March 2020 with no sign of a lending explosion. The multiplier remains a good way to see that banks multiply money; it is a poor description of what restrains them.

Central banks and the interest rate

A central bank (the Federal Reserve, the European Central Bank, the Bank of Japan, Banco de México) sets the short-term interest rate and, through it, the price of borrowing for the whole economy. Raise it and mortgages, car loans and business investment get dearer; spending cools, and so does inflation. Cut it and the reverse. The effects arrive slowly, with a lag of a year or two, which is why steering resembles driving with a delayed windscreen.

A simple benchmark is the Taylor rule (John Taylor, 1993): set the rate at inflation plus a neutral real rate of 2, nudged up by half the gap between inflation and the 2% target, and by half the output gap (how far the economy is above or below its sustainable level).

Calm gives 4%. A slump with 0.5% inflation and a gap of −6 gives −1.25%, below zero: the rule asks for a rate the bank can barely deliver, and in reality the ECB's deposit rate went only to −0.50% in 2019. (Negative rates are the edge of what central banks do; this is the "zero lower bound" and the reason unconventional tools exist.) The real data show the rule is a yardstick, not a law. In June 2022 US inflation was about 9% and the Fed funds rate 1.21%: it then rose to 5.33% by August 2023, and the ECB's deposit rate went from 0% in July 2022 to 4% in September 2023, while euro-area inflation peaked at 10.6% in October 2022. As of September 2026 the Fed's rate stood at 3.75% against US inflation of about 4.0%, and the ECB's at 2.5% against euro-area inflation of 3.75% (FRED).

Fiscal policy and debt

Where the central bank has one lever, governments have two: spending and taxes. In a slump they can spend more or tax less to prop up demand, and the effect on output can exceed the cost because the first dollar is someone's income, who spends part of it, and so on. The size of this multiplier is among the most argued numbers in the field. It depends on whether the economy has slack, whether the central bank offsets it, and how the spending is financed.

The debt that results is a stock, and what matters is its size against income. Each year the ratio changes by the interest bill and growth: with r the interest rate and g the growth rate of the economy, debt as a share of GDP rises by roughly (r − g) times itself, less any primary surplus (revenue minus spending before interest).

Starting at 100% with r = g, debt stays at 100%. If interest is 5% and growth 1%, debt climbs to 321% in 30 years; a primary surplus of 3% of GDP holds it to 154%. Real gross government debt (IMF, 2024): Japan 214% of GDP, Italy 135%, United States 122%, China 91%, South Africa 76%, Germany 61%, Mexico 59%. Japan shows that high debt in your own currency, mostly owed to your own citizens and with low interest, can last for decades. It does not show it is free: the bill is a constant claim on tax revenue.

Business cycles, and the schools of thought

Economies do not grow smoothly. They alternate expansions and recessions, and those swings are the business cycle: the US unemployment rate went from 3.5% in early 2020 to 14.8% in April 2020 and back to 3.4% by April 2023, an unusually sharp, fast cycle caused by a pandemic. The deeper question is why demand slumps persist and what to do. Four schools give different answers, and the field has not declared a winner.

School	Core claim	Policy it favours
Keynesian (Keynes, 1936; today's New Keynesians)	Wages and prices are sticky, so demand shortfalls can leave people jobless for years.	Governments and central banks should lean against slumps and booms.
Monetarist (Friedman and Schwartz, 1963)	"Inflation is always and everywhere a monetary phenomenon": money growth drives prices, and the Great Depression was worsened by the Fed letting the money supply shrink.	Steady, rule-based money growth; central banks first fight inflation.
New classical (Lucas, Nobel 1995)	People form rational expectations, so they anticipate policy; the "Lucas critique" (1976) says models built from past data break when policy changes.	Predictable rules over discretion; structural supply-side reform.
Modern Monetary Theory (Wray, Mitchell, Kelton)	A government that issues its own currency can't run out of it; the real limit is inflation and idle resources, not debt.	Spend to full employment, tax to control inflation; job guarantee.

Each has a record. Keynes explained what the 1930s needed; the 1970s stagflation, with high inflation and high unemployment together, embarrassed the simple Keynesian model. Monetarism helped end that inflation (Paul Volcker's money squeeze, 1979 to 1982) but the link between money and spending became unstable, so central banks moved to targeting inflation and setting interest rates directly. New classical ideas reshaped how models are built. MMT is a minority view: a 2019 University of Chicago IGM survey of leading economists unanimously rejected claims it attributed to MMT, while its supporters say they were being asked trick questions. The mainstream since the 1990s, "new Keynesian", blends sticky prices with rational expectations. Read the claims, not the labels.

What a graduate just sees

• A few percent a year, compounded, separates rich countries from poor ones; divide 70 by the growth rate to get the doubling time.
• GDP counts activity, not welfare. Look at it per person and in real terms.
• Saving raises the level of income; only new ideas and skills raise its long-run growth.
• Your inflation is your basket's inflation, and a 2% target is a choice, not a fact.
• Unemployment is a pool: layoffs flow in, hiring flows out, and slow hiring is what makes slumps hurt.
• Banks create deposits when they lend. The brake is borrowers, capital and the policy rate, not a stock of reserves.
• A central bank has one lever, the short rate, and it works with a lag.
• Debt ratios move with r − g. Growth is a debt policy.
• Know which school is speaking, and what evidence would change its mind.

Where it shows up next

• International Trade & Finance (34/47): the same accounts with an exchange rate; why currencies move and who wins and loses from trade.
• Development Economics (34/48): the growth table above, and the argument over why some countries stayed on the slow row.
• Public Economics (34/49): the other half of fiscal policy, what taxes and transfers do to people rather than to the aggregate.
• In the world: your mortgage rate, your wage negotiation, a company's investment decision, and the central bank announcement you read about this week.

If you want to go deeper

• 📘 Textbook. N. Gregory Mankiw, Macroeconomics (Worth/Macmillan). The standard intermediate text, with the Solow model and the schools set out clearly.
• 📘 Textbook. Olivier Blanchard, Macroeconomics (Pearson). The other common choice, built around a single coherent model and recent episodes.
• 📘 Gentler. Charles Wheelan, Naked Economics (W. W. Norton), or CORE Econ's free text The Economy, whose macro units follow growth, unemployment and inflation with real data.
• 🌐 Free course. MIT OpenCourseWare 14.02 Principles of Macroeconomics (Spring 2023). Also Khan Academy Macroeconomics.