King and Plosser - Real Business Cycles — reading pack

Page: https://gautsch.org/research/king-and-plosser-real-business-cycles/

How to use this pack

Help the reader explore this rabbit hole. Start by asking what caught their attention, then discuss one question at a time. Explore the strongest counterargument and what remains uncertain. Distinguish the original speakers’ claims, Adam’s question, the site’s research commentary, and your own interpretation. Do not treat the commentary as a transcript or assume Adam endorses every claim. Preserve corrections and uncertainty; do not invent sources or pretend to have opened links.

This pack contains the page’s current research text, references and figure text. Related rabbit holes are linked, not included. It is a reading companion, not an independently verified source.

The short version

Adam asked “Who?” and, separately, what Tyler is getting at. Who: Robert King and Charles Plosser, two of the builders of real business cycle theory. John Long and Plosser’s 1983 “Real Business Cycles” is one of its foundational papers, alongside Finn Kydland and Edward Prescott’s “Time to Build and Aggregate Fluctuations” (1982). What Tyler is getting at: he is accusing Acemoglu — a left-leaning economist who has spent his career on market failures — of having quietly adopted the macro of the freshwater right. And the accusation lands, which is why the exchange is fun.

Relevant transcript excerpt

Source: https://conversationswithtyler.com/episodes/daron-acemoglu-2/

Annotated transcript: https://gautsch.org/research/#a19

COWEN: Does that mean you’re not really such a Keynesian? Because the fertility crisis, aggregate demand, aggregate supply, they’re shrinking forever. A Keynesian or a supply-sider could get quite worried. Paul Romer, the market size is shrinking, he should get quite worried. In a funny way, you end up at a real business cycle point of view where as long as the induced innovation is positive, the macro will go fine. You’re like Long and Plosser, King and Plosser in your macro. Is that wrong?

Research commentary

Adam asked: “I’d love a little rabbit hole expanding on this paragraph. Explain what Tyler is getting at.” and “Who?”

Who they are

Cowen says “Long and Plosser, King and Plosser” — he is naming the pair of collaborations, not confusing himself.

What real business cycle theory claims

The provocative core: in the benchmark model, recessions are not failures. They are the efficient response of a well-functioning economy to real shocks — mostly shocks to productivity.

• The driver is technology, not money or demand. In the basic models money plays little or no role.
• Employment falls in a downturn because workers choose less work when the real wage is temporarily low (intertemporal substitution of labor).
• Within the benchmark — competitive markets, flexible prices, no externalities or missing markets — the outcome is Pareto-efficient, so stabilization policy has nothing to fix there. That conclusion is a property of those assumptions, not a finding about actual economies; add frictions to the same framework and policy can matter again, which is roughly what the New Keynesian models that descend from it do.
• The residual — the unexplained part of growth, “total factor productivity” — is treated as the fundamental driving force.

It was, and is, deeply contested. The standard objection is that it requires believing the Great Depression was a large voluntary vacation. But its method won even where its conclusions didn’t: RBC established the calibrated microfounded model as the standard tool, which is why every modern DSGE model is a descendant.

What Cowen is actually saying

Follow the logic of his question:

“Does that mean you’re not really such a Keynesian? Because the fertility crisis, aggregate demand, aggregate supply, they’re shrinking forever. A Keynesian or a supply-sider could get quite worried. Paul Romer, the market size is shrinking, he should get quite worried. In a funny way, you end up at a real business cycle point of view where as long as the induced innovation is positive, the macro will go fine. You’re like Long and Plosser, King and Plosser in your macro.”

The argument step by step:

1. Falling birth rates shrink both demand and supply, permanently.
2. A Keynesian should fear the demand side — fewer people, less spending, chronic shortfall.
3. A Romer-style growth theorist should fear the supply side — ideas depend on the number of people looking for them, and a smaller market means weaker incentives to innovate. (Romer’s own model makes population a driver of growth.)
4. Acemoglu fears neither as much, because his paper finds falling birth rates associated with faster growth per working-age adult and argues technology responds: scarce labor induces labor-saving innovation.
5. That is an RBC-shaped answer. The real side — technology, the residual — determines outcomes; demand doesn’t matter much; the economy self-corrects through the productivity channel without policy.

Cowen’s next line makes the target explicit: “It’s about the residual, and if the residual is—” The residual is TFP, the thing RBC theorists put at the center.

So the jab is: the market-failure economist has ended up at a self-correcting-economy conclusion.

Acemoglu’s answer

Three moves, and they’re worth separating:

1. He doesn’t recognize the framing. “I never thought of King and Plosser about induced innovation.” Honest — he came to this through the growth-theory literature, not the macro one.
2. He supplies his own ancestor instead: “Habakkuk was the first one who was about this.” See Induced Innovation and the Habakkuk Thesis. This is him saying: my lineage is 19th-century economic history, not 1980s Minnesota macro.
3. He half-accepts the charge: “I never saw myself as a traditional Keynesian… and I never understood the new Keynesian models very well.” But he keeps a demand channel — “there are episodes in which aggregate demand shortages create problems” — and argues the fertility decline is too slow-acting to produce one.

The honest bit: “I’m also finding these results surprising. We’ve checked them so many times, and that’s why we’ve done them so many different ways, but it seems to be there in the data.” He presents it as a result that surprised him and survived repeated re-checking. What he wanted the answer to be is not something the transcript establishes.

Reading

• Long & Plosser, “Real Business Cycles,” JPE 1983 — a foundational paper
• Kydland & Prescott, “Time to Build and Aggregate Fluctuations” (Econometrica 1982) — the other one, and the start of the calibration method
• King & Plosser, “Money, Credit and Prices in a Real Business Cycle,” AER 1984
• Summers, “Some Skeptical Observations on Real Business Cycle Theory” (1986) — the classic demolition, four pages, entertaining
• Romer, “Endogenous Technological Change” (1990) — the position Cowen says should worry

Working notes

Cowen’s “you’re like Long and Plosser” is a compliment and a needle at the same time, which is characteristic. The substantive question underneath — is induced innovation a self-correcting mechanism strong enough to make demographic decline harmless? — is genuinely open, and The Lucas Critique is the strongest reason to doubt it.

Corrected 2026-09-18. Earlier drafts called Long & Plosser 1983 “the founding paper,” which leaves out Kydland & Prescott 1982, and stated RBC’s efficiency and no-stabilization conclusions as if they held unconditionally. They hold inside the benchmark assumptions. Step 4 of Cowen’s argument also now says what the Baby Busts paper reports (an association) rather than a law.

Checked against the book: not there. No real-business-cycle literature, no Long and Plosser, and no treatment of demographic decline as a growth question. The Baby Busts result Cowen presses him on is a working paper, not book material. What the book does supply, in Chapter 6, is the empirical half of the induced-innovation argument underneath this exchange — German firms adopting robots faster than American ones and reallocating rather than shedding workers, which is automation responding to institutions rather than to scarcity. See Acemoglu and Restrepo - The Task Framework. The open question below — whether induced innovation is self-correcting enough to make demographic decline harmless — gets no help from the book either way.

Checked against the audiobook edition (Penguin Random House Audio, narrated by John Lee), machine-transcribed; references are by chapter.

Related: Induced Innovation and the Habakkuk Thesis · The Lucas Critique · Acemoglu and Restrepo - The Task Framework

Research page built in conversation with Claude.