Case Study 2 — Why Two Reasonable Economists Disagree About the 2021–2023 Inflation

In April 2021, the U.S. inflation rate (measured by the Consumer Price Index) was 4.2% — the highest figure in over a decade. By June, it was 5.4%. By June 2022, it was 9.1%, the highest in 40 years. Then it began to fall. By June 2023, it was 3.0%. By early 2024, it was approaching the Federal Reserve's 2% target. The episode was the largest sustained inflation surge in two generations and the most consequential monetary policy event of the post-pandemic era.

It is also a perfect case study in why economists disagree.

Three serious schools of explanation for the inflation surge formed roughly in real time, and a fourth crystallized after the fact when the inflation began to fall. None of the four can be ruled out cleanly even now. Each has evidence in its favor. Each is held by serious, credentialed economists who are not stupid and not dishonest. The fact that they cannot agree — even with several years of hindsight, even on something as well-measured as the inflation rate — is not a bug in the field. It is what genuine empirical disagreement looks like in real time.

This case study walks through the four explanations and asks which kind of disagreement (facts, models, values, time horizons) drives the dispute among them. The answer, you'll see, is "all four."

Explanation 1: It was demand-driven (the "stimulus was too big" view)

The first explanation, championed early and loudly by Larry Summers (former Treasury Secretary, former Harvard president, lifelong centrist Democrat), Olivier Blanchard (former IMF chief economist), and others, is that the inflation was driven primarily by demand. The argument: the U.S. government spent over $5 trillion on COVID relief between 2020 and 2021 (CARES Act, Consolidated Appropriations Act, American Rescue Plan) — far more than the size of the economic shock the relief was supposed to offset. That spending put a lot of money in households' bank accounts at a time when supply was constrained by pandemic disruptions. When the constraints lifted and households spent the money, demand outran supply, and prices rose.

The model is roughly the standard aggregate-demand-driven inflation story: too much money chasing too few goods. The implication is that the inflation was largely the Fed's and the Treasury's fault — specifically, the fault of the 2021 American Rescue Plan, which Summers warned (in February 2021) would be inflationary. He was right about the direction. The debate is over how right he was about the size and what should have been done differently.

Explanation 2: It was supply-driven (the "supply chains broke" view)

The second explanation, championed by Janet Yellen (then Treasury Secretary), Jerome Powell (Fed Chair) for much of 2021, and many others, is that the inflation was driven primarily by supply disruptions. The argument: COVID broke global supply chains — closed factories in China, disrupted shipping routes, reduced workforce availability in trucking and logistics, oil supply shocks from the Russia-Ukraine war. These were one-time supply shocks that pushed up the cost of producing goods, and the cost increases got passed on to consumers as price increases. The inflation was real but transitory: as supply chains healed, prices would stabilize and then come back down.

The model is roughly the cost-push or supply-shock inflation story. The implication is that the right policy response was largely patience — wait for supply to recover, don't tighten monetary policy aggressively because that would just produce a recession on top of an already-broken economy. This is what the Fed did, more or less, through 2021. By early 2022, when inflation was clearly not transitory, the Fed pivoted to aggressive tightening. The "transitory" framing was widely mocked in retrospect.

Explanation 3: It was both (the "fiscal stimulus into a constrained economy" view)

The third explanation, which became consensus among many academic economists by mid-2022, is that the surge was both — and that the interaction between the two made the total effect bigger than the sum of the parts. The fiscal stimulus alone would have produced some inflation. The supply disruptions alone would have produced some inflation. But large stimulus injected into a supply-constrained economy is a particularly potent inflationary cocktail, because firms cannot expand output to meet the new demand (supply is constrained), so the demand instead gets transmitted directly into higher prices.

The model here is a hybrid: aggregate demand and aggregate supply both shifting in inflation-producing directions. The implication is that the policy debate is harder than either single-factor story makes it sound. You cannot blame only the stimulus or only the supply chain; both contributed; the interaction mattered; and reasonable people can argue about the relative weights.

Explanation 4: Expectations and luck (the "soft landing" view)

The fourth explanation, which crystallized when inflation started to fall faster than most forecasters expected starting in late 2022, focuses on expectations and the role of central bank credibility. The argument: inflation expectations stayed anchored — that is, households and firms continued to believe the Fed would eventually bring inflation back to 2% — even as actual inflation rose. This anchoring was a real achievement of decades of Fed credibility-building (going back to the Volcker disinflation of the early 1980s). Because expectations stayed anchored, the inflation did not become self-reinforcing the way it had in the 1970s. When the Fed did tighten and supply chains did heal, inflation came back down without requiring the deep recession most economists had predicted would be necessary.

This is partly a story about a feature of the model (inflation expectations matter, and anchoring matters), partly a story about a contingent fact (the Fed had built enough credibility that anchoring held), and partly a story about luck (the supply-chain healing happened to be timed with the monetary tightening, so it's hard to disentangle which mattered more). The Fed's preferred interpretation of the episode is that monetary policy worked as designed; some critics argue that the Fed got lucky and is taking credit for outcomes that happened despite, not because of, its actions.

Where the disagreement lies

Sort the disagreement among these four explanations into the four buckets from §2.5.

Disagreement about facts. There is real disagreement about what the data show. Did the American Rescue Plan really put as much money into the economy as the demand-driven story claims? (Yes, in dollar terms; the question is how much was spent versus saved.) How much of the price increase in 2021–22 was driven by goods (more supply-chain story) versus services (more demand story)? Was the labor market tight enough in 2022 to drive a wage-price spiral? Different economists looking at slightly different slices of the data tell slightly different stories.

Disagreement about models. There is real disagreement about which model best fits the data. The pure demand-side story comes from a model in which AD shifts dominate. The pure supply-side story comes from a model in which SRAS shifts dominate. The hybrid story uses both. The expectations story brings in inflation expectations as an additional channel. Each model can fit the data with appropriate parameters; the question is which model is the best description of what was actually happening.

Disagreement about values. This is more subtle but real. Economists who place high weight on labor market outcomes (low unemployment) tend to be more sympathetic to the "patience" view, because they don't want to risk a recession. Economists who place high weight on price stability tend to be more sympathetic to "tighten quickly," because they fear inflation expectations becoming unanchored. These value differences shape which model the economist defaults to and which evidence they find persuasive.

Disagreement about time horizons. Was the inflation surge "transitory"? In one sense, obviously yes — it lasted about three years and then went back to roughly the target. In another sense, obviously no — three years of high inflation is a real cost to households and a real test of central bank credibility. Whether you think the Fed was right to be patient depends partly on how you define "long enough to wait."

You can see all four of these at work in any serious discussion of the 2021–2023 episode. If you read the Brookings Papers on Economic Activity or the Journal of Economic Perspectives from 2022–2024, you'll see economists wrestling with each of the four kinds of disagreement, often in the same paper.

What this case study illustrates

The point is not to tell you which explanation is right. The point is to show you what real, serious economic disagreement looks like — and to argue that the existence of the disagreement is not a sign that economics is broken.

A field that could not produce four distinct and serious explanations for the 2021–23 inflation, each with respectable empirical and theoretical support, would be a field that was overconfident. The honest position is something like: "All four explanations have merit; the data is consistent with multiple framings; it will probably be at least a decade before we have enough perspective to give a confident answer; and reasonable people working in good faith can disagree about which explanation is most central."

This is what serious economic analysis looks like in real time. It is uncomfortable. It does not give you the satisfying clarity of a single right answer. But it is honest in a way that confident single-answer explanations are not.

A note about Larry Summers and the value of being publicly wrong

Larry Summers was one of the very few economists who, in February 2021, predicted publicly and forcefully that the American Rescue Plan would produce significant inflation. Most of the profession — including most of the people running the Fed and the Treasury — thought he was overreacting. He was largely right.

This is worth noting for two reasons. First, it shows that economic models can generate genuine, testable predictions, and economists who use them carefully can see things others miss. The 2021 inflation surge was not entirely unforecastable. Summers used a fairly standard demand-side model and applied it carefully, and the model gave the right answer. That is a victory for economic modeling — not a defeat.

Second, the same Larry Summers was wrong about other things in his career. He was wrong about financial deregulation in the 1990s. He was wrong about the optimal size of the 2009 stimulus (he initially supported a smaller package than the one that was ultimately needed). The lesson is not that Summers should be canonized; it is that even the smartest economists are right sometimes and wrong sometimes, and the field's task is not to identify The Smartest Economist but to make sure that disagreement is informed and that the right voices are heard at the right times.

When you read economic news, look for the people who are willing to be publicly wrong. They are usually the ones who have the most to teach you, even when they're wrong, because their reasoning is exposed and checkable. The people who are always right in retrospect — who claimed credit for being right after the fact, but didn't put their predictions on the record — are usually less informative.

Discussion questions

1. Of the four explanations for the 2021–23 inflation surge, which one do you find most persuasive? What evidence would change your mind?
2. The chapter argued that economic disagreement is "a feature, not a bug." Does this case study support that claim? Or does it suggest that economics should aspire to more agreement?
3. Larry Summers was right about the 2021 inflation surge largely because he used a standard model that other people were ignoring. What does this say about the value of standard models versus the value of "thinking outside the box"?
4. The Fed's "soft landing" — bringing inflation down without a recession — was widely considered impossible by most forecasters in 2022. Was the Fed lucky, or skillful, or both? How could you tell?
5. Imagine the same inflation surge happens again in 10 years. Which of the four explanations (or some combination) would you reach for first? What additional evidence would you want?