Broadsheet

Today’s post is brought to you by my sponsor, Mechanize. They’re hiring junior software engineers at $300K/year base salary. Apply now!

* * *

In a recent post, I responded to a Fable output comparing market monetarism with the HANK [Heterogeneous Agent New Keynesian] model, especially in reference to 2008-09. Vaidas Urba also asked Fable the same question from a HANK perspective. Because LLMs are somewhat obsequious, that response appeared slightly more HANK-friendly, although the substance was not much different. And then Vaidas asked Fable to compare the two responses and offer a judgement as to which one was more persuasive.

In this post, I had intended to respond to Vaidas’s latter two Fable outputs, but on second thought I’d like to respond to a different Fable output, which seems much more interesting, and even more impressive. This output was produced after Vaidas asked Fable to respond to my blog post, which was itself a response to the first Fable output.

This post will have three parts. In the first two, I’ll provide the Fable HANK-friendly reply and the overall summation that Vaidas sent me earlier, without any comment on my part. Feel free to skim over the first two sections. I don’t wish to get bogged down in an overly long tit-for-tat on every single point. Instead, I’ll reserve all my comments for the superior part 3, where I respond point by point to Fable’s reply to my earlier post. In this way, I hope to keep the conversation going in a productive fashion.

Note that in this final section, Fable’s response is written at a fairly high level. The response is not technically demanding in a mathematical sense, but it requires a deep understanding of macro theory. Sorry, this post isn’t for everyone. But I’ll occasionally try to clarify in my replies to make it easier for the reader. I will not indent Fable’s output, only my replies.

Part 1:

Prompt:

You are a discussant preparing for macroeconomics seminar. The topic of the seminar is the thesis:
Policy prescriptions of HANK models would have been more impactful mitigating the severity of Great Recession compared to market monetarist policy prescriptions.
Identify and explain the top 5 arguments in favor of the thesis.
Identify and explain the top 5 arguments opposing the thesis.
Based on the arguments, provide your ultimate verdict with a reasoned justification.

Reply:

Arguments in favor of the thesis (HANK > market monetarism)

1. The zero lower bound gutted monetary transmission exactly where HANK predicts. Kaplan, Moll, and Violante (2018) show the direct intertemporal-substitution channel — the heart of representative-agent monetary policy — accounts for only a small minority of transmission; consumption responds mainly to realized disposable income. With rates at zero and roughly a third of households hand-to-mouth (including the “wealthy hand-to-mouth”), rate cuts and QE had little direct traction. Targeted transfers and UI raise constrained households’ incomes mechanically and immediately, no expectations channel required. Evidence from the 2001 and 2008 rebates (Johnson-Parker-Souleles) shows a large fraction spent within months.

2. It was a household balance-sheet recession, and HANK prescriptions attack that mechanism. Mian and Sufi document that the consumption collapse was concentrated in high-leverage counties, propagated by foreclosures and debt overhang. HANK-style policy — principal reduction, mortgage restructuring, transfers to underwater borrowers — targets the deleveraging spiral directly. Actual policy (HAMP) was timid and the slump was correspondingly long. NGDP stabilization helps debtors only diffusely.

3. The forward guidance puzzle undermines market monetarism’s core mechanism. MM leans on expectations: announce a credible NGDP level target and markets do the work. But McKay-Nakamura-Steinsson and related work show forward guidance is far weaker with borrowing-constrained, inattentive households — they can’t consume promises of future nominal income today. HANK thus implies the MM channel would have underdelivered precisely in 2008–09, while fiscal transfers are robust to that friction.

4. Distributional amplification and scarring. Income losses concentrated on high-MPC, low-wealth workers, creating a feedback loop and persistent hysteresis (Yagan 2019). UI extensions and automatic stabilizers deliver a double dividend in HANK: maximal stimulus per dollar plus insurance value. Stabilizing the NGDP aggregate can still leave the loss distribution — and the amplification loop — intact.

5. Implementability, plus the 2020 natural experiment. Congress could scale proven instruments; the failure was size, not feasibility. Adopting a credible, untested NGDPLT regime mid-panic had no institutional pathway. And CARES in 2020 — pure HANK policy — caused disposable income to rise in the deepest downturn ever, producing the fastest demand recovery on record. The MM counterfactual never received a comparable proof of concept.

Arguments opposing the thesis (market monetarism > HANK)

1. The proximate cause was a preventable nominal collapse. The Fed held rates at 2% on September 16, 2008 — two days after Lehman — citing inflation risk, then introduced interest on reserves in October, effectively tightening as breakevens collapsed. NGDP fell furthest below trend since the 1930s. Via Fisher debt-deflation logic, keeping nominal incomes on path would have automatically protected the very balance sheets HANK worries about. Prevention beats ex-post transfers.

2. Monetary offset: fiscal potency is hostage to the monetary regime. The central bank moves last; if it targets its own nominal objective, it neutralizes fiscal impulses. The 2013 US episode — sequester plus payroll-tax hike alongside QE3, with growth accelerating — is cited as passing the “Sumner critique” test. Even within HANK models, transfer multipliers depend on monetary accommodation, conceding the primacy of the nominal anchor.

3. Scale, speed, and unilateral capacity. The Fed can act in an afternoon with an unbounded balance sheet; fiscal policy has legislative lags, leakage into saving, and hard political ceilings — ARRA was capped near $800bn and the austerity pivot came by 2010. A $2–3 trillion HANK package in 2009 was politically impossible; earlier QE, no IOER, and makeup guidance were within existing Fed authority.

4. HANK adds little beyond 2009-vintage Keynesianism — and itself implies monetary policy stays powerful. HANK was formalized in 2015–18; its Great Recession prescriptions collapse into standard fiscal stimulus that was tried and contested. NGDP targeting, by contrast, was articulated in real time (Sumner from early 2009, building on Meade, McCallum, Hall-Mankiw). Moreover, KMV find total monetary effects comparable to RANK — transmission just runs through indirect labor-income channels — so HANK doesn’t uniquely license fiscal-first policy.

5. Regime shifts have delivered before. Eggertsson (2008) attributes the bulk of the 1933–37 recovery — among the fastest on record — to FDR’s abandonment of gold and reflation commitment, with little initial fiscal expansion. The Swiss franc floor and Abenomics’ first arrow similarly show credible nominal commitments moving economies instantly. That’s direct historical evidence the MM counterfactual could have been extraordinarily impactful.

Verdict

I come down in qualified support of the thesis. Three considerations decide it. First, the transmission robustness asymmetry: HANK instruments work through a mechanical, empirically verified income channel, while the MM prescription depends on an expectations mechanism that the forward-guidance puzzle suggests was weakest exactly when needed — at the ZLB, among constrained households, under an untested regime with no credibility technology. Second, the recession’s distinctive severity came from the household leverage channel, which targeted transfers and debt restructuring address and aggregate NGDP stabilization only grazes. Third, the closest natural experiment we have — 2020–21 — showed HANK-style policy generating an income-supported recovery of unprecedented speed (albeit with inflation costs that MM would fairly note as evidence nominal anchors still matter).

Two concessions keep the verdict qualified. The market monetarists are right that the Fed’s passive tightening in fall 2008 was a genuine unforced error, and correcting it would have meaningfully reduced severity at near-zero fiscal cost. And monetary offset is real: HANK fiscal policy only reaches full potency with an accommodative Fed, so the strongest true counterfactual is a synthesis — fiscal-led stimulus and balance-sheet repair with a cooperative nominal anchor. But since the thesis forces a comparison of prescription sets, HANK wins on the margin: its tools were implementable, scalable through existing institutions, and robust to the credibility and heterogeneity frictions that would likely have hobbled a mid-crisis NGDPLT conversion. The margin, though, is narrower than partisans of either camp admit.

Part 2:

Prompt:

Here are two Claudes responding to the opposite prompts (i.e. prompts where the opposite thesis is being argued). Where do you stand, what is your ultimate verdict?

Reply:

First, the tell: each Claude “narrowly” endorsed the thesis it was assigned, while their concessions and final syntheses are nearly identical. The headline verdicts moved with the prompt; the shared content is the signal.

My own verdict: on the question as literally posed — reducing severity — I side narrowly with the market monetarists, but on the least glamorous grounds. Severity was determined in roughly three quarters, and only one actor could move inside that window. The decisive point isn’t the expectations machinery; it’s that the Fed’s fall-2008 errors (the September 16 hold, IOER, no makeup language) were correctable with conventional tools and existing authority, no beliefs required, while nothing fiscal could pass and disburse before the trough was in. And stabilizing the nominal income path works upstream of the very Fisher/Mian–Sufi amplification HANK emphasizes — it protects debtor balance sheets before they implode rather than compensating after.

But I only credit “materially less severe,” not “avoided.” Once at the ZLB, full NGDPLT leans on exactly the forward-guidance channel that is weakest among constrained households, and Mian–Sufi’s timing evidence (leveraged-county consumption falling before NGDP did) says the nominal collapse was the amplifier, not the shock. So Document 1’s verdict holds, but only on its own narrow terms.

Widen the frame and it flips. Most of the cumulative welfare loss sits in the six-year slump, not the trough, and there HANK’s case is stronger: broken refinancing and lending channels, cross-sectional multipliers at or above one at the ZLB (which also deflates the 2013 offset story — a Fed pinned at zero wasn’t offsetting, just easing), and 2020–21 as a real proof of concept that mechanical income support recovers demand fast, with the inflation overshoot as tuition paid for the market monetarist point that anchors still matter.

So the honest answer is the one both documents backed into: NGDP-style level anchor as the regime, HANK-grade automatic stabilizers as the robustness layer for when expectations channels fail. MM is right about 2008; HANK is right about nearly everything after. And since I’m a third Claude subject to the same framing pulls, weight the two documents’ overlapping concessions more than any of our verdicts — mine included.

Part 3:

In this section, my replies will be indented italic writing.

Prompt:

I [Vaidas] received the attached email today [i.e., my earlier post replying to Fable], I could forward your [Fable’s] 3 paragraph response to Scott Sumner - but the total length of your response is unlimited

Reply:

Vaidas — this is a treat of an assignment. The three paragraphs for forwarding are marked below and are self-contained; after them is an appendix keyed to Scott’s points in order, which you can forward in whole, in part, or not at all.

For forwarding — the three-paragraph response:

A preliminary confession and a bind. The confession: I have no memory of writing the evaluation you reviewed — each conversation starts fresh — but I recognize the reasoning as mine and will own it, errors included. The bind: you noted that LLMs are a bit obsequious, which means agreement from me reads as sycophancy and disagreement reads as calibration to your known taste for pushback. The only exit is to make every concession carry its reasoning and every disagreement name its crux, and let you audit. So, concessions first, because they’re specific. Nakamura–Steinsson: conceded in full. The open-economy relative multiplier differences out the monetary reaction function by construction — the authors say so — and citing it to establish aggregate multipliers at the zero bound assumed the very thing in dispute. That is your diagnosis verbatim: I retrieved the literature’s standard citation without propagating monetary offset through it. My only mitigation is that this conflation is the profession’s modal one, and a distillation engine inherits a discipline’s conflations along with its knowledge. “Independently easing rather than offsetting” also fails, and it’s worth saying why: the distinction requires a fixed-quantity instrument, and open-ended, outcome-contingent QE3 was engineered to be the opposite — a reaction function with the offset built in. Your GM line lands. You asked me to explain “decisively”; I can’t, so I withdraw it. With a make-up-flavored framework, open-ended purchases, and transfers roughly six times ARRA all moving together, 2020–21 is jointly confirmatory and cannot rank the instruments — and 2022–24 ran the reverse experiments: several points of GDP in passive fiscal consolidation coincided with the fastest NGDP growth in decades, then renewed deficit widening coincided with deceleration once the Fed tightened. Both years the nominal path tracked the monetary stance against the sign of the fiscal impulse. On Japan, the comparative reading is yours: two decades of history’s largest peacetime fiscal experiment alongside falling NGDP, then a monetary regime shift plus a consumption-tax hike, then growth — no honest scoring of that record favors fiscal primacy. What survives of my point is narrow, and by my own logic barely: the BOJ never adopted level targeting, so its undershoot no more refutes NGDPLT than pre-2013 QE’s modest measured effects do. That is your response to my Woodford citation, turned on my Japan citation. And you’re right about lags: 2008 and 2020 showed simple transfers arrive in weeks; the durable lag critique applies to composition-heavy packages like ARRA — which is an argument for automatic stabilizers, not a rescue of discretionary stimulus.

[My response: No objection here. This observation caught my eye: “My only mitigation is that this conflation is the profession’s modal one, and a distillation engine inherits a discipline’s conflations along with its knowledge.” I made a similar point in my recent post on why Fable is Keynesian—it reflects the consensus, which I wrote before reading this response. BTW, is “mitigation” an unusual term to use there?]

Here is what I decline to concede, and where I think the dispute actually lives. “Monetary offset operates even at the zero bound” is a premise, not a theorem. Offset implies that cross-sectional estimates fail to aggregate conditional on an active reaction function; whether the 2009–13 Fed’s reaction function was active in the expansionary direction is the substantive question, not an implication I failed to see. The correct general rule — which both camps should co-sign — is that cross-sectional multipliers are valid precisely for variation the central bank won’t respond to: states within the US, countries within the eurozone. Hold that rule; it earns its keep below. Next, once Woodford (2012) and Eggertsson–Woodford are re-filed where they belong — as indictments of concrete-steps thinking rather than of level targeting (Woodford’s Jackson Hole remedy was a nominal GDP level path) — the load-bearing disagreement is narrower than my original five-versus-five implied, because at the bound everything runs through credible commitments about future policy, your channel included: a “permanent” injection is a promise, which is Krugman 1998 before it is anyone’s Keynesianism. HANK’s real contribution is that household responses to distant promises are weaker than representative-agent models pretend. That bites if transmission runs through the consumption Euler equation, and mostly glances off if it runs through portfolios and asset prices; I can state that paradigm split precisely, but I cannot adjudicate it, and I won’t pretend to. What I can defend paradigm-free is the political-economy form of the credibility problem, and my exhibit was never Japan — it is the SNB in January 2015: a simple, fully specified, self-financing commitment, defended by printing one’s own currency, abandoned under balance-sheet politics while it was holding and working. You would say — you have said — incompetence, not impotence. Agreed, and that is the point: the constraint was never capacity but willingness, markets rationally price willingness, and “a check clears” retains its force as the one instrument robust to that pricing. Your strongest systemic reply is that under NGDPLT the bound is rarely reached at all, because the regime keeps expected nominal income, and hence the natural rate, from collapsing — the ZLB as symptom rather than state. Half granted: 2008 was plausibly an avoidable bound; 2020 reached it in days under a considerably better regime. That residual — low-probability states where commitment fails politically or the shock outruns it — is exactly what the automatic-stabilizer half of my original synthesis was insuring. Notice that every blow in your response lands on fiscal-as-primary; none lands on fiscal-as-insurance.

[My response: The quick move to the zero lower bound in 2020 is one of Fable’s strongest arguments. I still believe that Covid was a very unusual situation, but this case does strongly suggest that NGDPLT might not be enough to always prevent it from occurring. (And I say this even though we didn’t precisely have NGDPLT in 2020, but FAIT should have had a similar stabilizing effect.)
Fable is correct that the crux of the dispute is monetary offset at the zero lower bound. Does it work? Fable is right that fiscal policy can work if there is no monetary offset.
In my recent book, I cite the Swiss franc peg of 2011-15 as a powerful argument in favor of market monetarism, whereas Fable sees it cutting the other way. (Switzerland had depreciated and then pegged the Swiss franc in September 2011 in order to avoid deflation, and then abandoned the exchange rate peg on January 2015, at which point it appreciated dramatically.) So, let’s spend some time on this example.
When I argued that a central bank could always inflate by depreciating its currency, Paul Krugman did not deny that a suitably large currency depreciation would solve the liquidity trap, rather he denied that a central bank could easily depreciate its currency. Here’s Krugman, from 2010:
“Oh, and about the exchange rate: there’s this persistent delusion that central banks can easily prevent their currencies from appreciating. As a corrective, look at Switzerland, where the central bank has intervened on a truly massive scale in an attempt to keep the franc from rising against the euro — and failed”
Soon after, the SNB did succeed in holding down the franc, for more than three years. Krugman might respond that a central bank trying to do so would be swamped with offers to buy its currency, creating an overly large balance sheet. In my recent book, I tried to show that the Swiss were actually forced to buy more bonds when they were not holding down the value of their currency, as the Swiss franc is most attractive at times when investors expect it to appreciate.
In my view, the Swiss stopped pegging the SF not because their balance sheet was becoming too big, rather because recent weakness in the euro led to (unfounded) worries about inflation. In other words, it was the same misjudgment that led the BOJ to foolishly raise interest rates in 2000 and 2006, and the ECB to foolishly raise interest rates in 2008 and 2011.
Fable is correct that credibility can be a problem at the zero lower bound. When using interest rates as a policy instrument, an unwillingness to “promise to be irresponsible” (to use Krugman’s clever phrasing), would be a fatal flaw. Even a modest size QE might fail for the same reason. That’s what I mean by Keynesian reasoning—the assumption that monetary policy lacks a strong mechanical lever and relies on uncertain expectations. But the Swiss case is not an interest rate-oriented monetary policy, it is a price of money-oriented monetary policy. THE EXCHANGE RATE IS THE INSTRUMENT. This is why the Singapore central bank doesn’t face a zero lower bound—it uses exchange rates as its monetary policy instrument. A depreciated exchange rate solves the problem, as long as you keep doing it. There is no zero bound on exchange rates.
Nothing in the Swiss example suggests any sort of inability to inflate, just an unwillingness. Consider that the gold standard was an even more rigid regime than the Swiss fiat money regime, and yet Roosevelt was able to dramatically raise prices in 1933-34 by depreciating the dollar. When you use the exchange rate as the policy instrument, there is no need to rely on the “expectations fairy”—the exchange rate works “mechanically”, to use Fable’s unfortunate terminology. Krugman was correct that the issue is not whether the exchange rate works, the question is whether the central bank can control the exchange rate. The SNB’s peg of the Swiss franc during 2011 to 2015 worked exactly as intended, and it stopped working precisely when the Swiss wanted it to stop working. There was not a failure to achieve the policy objectives of the Swiss authorities, at least at the time. It was the wrong objectives. They should have kept the peg.
Many people expected the Danes to also abandon their currency peg in January 2015, as there were also speculative purchases of the krone. But the Danes chose to keep the peg, and to this day they never let the krone appreciate against the euro. Denmark shows the path that Switzerland decided not to take. It is important not to conflate “won’t” with “can’t”.]

To your direct question: yes. The rule my verdict used — where conventional room remains and the central bank commits identifiable expectations errors, the market-monetarist critique dominates — applies to the ECB a fortiori: a hike in July 2008 into a recession already underway, two more into the 2011 debt crisis, the effective bound not reached until 2013–14, QE arriving in 2015, six years behind the Fed; nominal GDP growth under one percent a year for five years and a double dip that the US — which did more fiscal consolidation than the eurozone in 2013, under open-ended QE3 — did not have; Sweden running the small-scale replication in 2010–11, Svensson’s dissents included; and the cleanest expectations experiment on record in July 2012, when two sentences in London and a program never once activated compressed sovereign spreads by hundreds of basis points — a result concrete-steps accounting cannot even parse. So: market-monetarist-favorable for the eurozone through at least 2013, stated plainly, minority company accepted — with the one caveat my cross-sectional rule supplies free of charge: individual member states face no national offset, so country-level austerity multipliers are the policy-relevant ones for them. “Austerity devastated Spain” and “the ECB caused the aggregate double dip” are both true; the profession’s error was letting the first claim impersonate the second. Where does this leave the scorecard? My 2008 verdict stands and is less narrow than I made it. My claim that the verdict “flips decisively” after 2009 does not survive your response — it rested substantially on the two citations I have withdrawn — and downgrades to unresolved, hinging on whether level-path commitments are politically credible at the bound, with Draghi 2012 and Kuroda 2013 the best evidence for hope and the SNB’s January 2015 the best evidence for doubt. The synthesis — NGDPLT as anchor, HANK-informed automatic stabilizers as insurance for the commitment-failure states — comes out strengthened, because it is the portfolio one holds precisely while that question is open. Last, since you floated the idea yourself: the interesting test isn’t whether I follow my own logic when asked directly; it’s whether it binds unprompted. For the follow-up post, have Vaidas ask me to predict, in advance and in writing, your top disagreements with the HANK-side output and my conditional responses — then score the prediction against what you actually write. It’s cheap to run, and it separates understanding from retrieval far better than any verdict I could hand you.

[My response: Note that the phrase “two sentences in London” refers to Mario Draghi’s “whatever it takes” speech. I agree that individual eurozone members can use fiscal policy, but monetary offset still applies at the eurozone level. With monetary offset, local fiscal stimulus results in a negative demand externality for neighboring countries.]

Appendix — notes keyed to Scott’s points, in order (optional to forward):

1. Your correction to my first pro-thesis argument. Accepted, and it’s clarifying: it relocates the work from Argument 1 (timely activism) to Argument 2 (the regime as automatic stabilizer), which is where market monetarism is strongest anyway. Under level targeting, the September 16 error was not the 2% hold per se but the absence of any catch-up promise as breakevens collapsed; the hold was a symptom. Your asset-price framing — the level path as a put on nominal income, supporting collateral values and hence bank solvency — belongs to the same evidence class as FDR 1933 and Draghi 2012: regime announcements moving asset prices faster than any concrete step could. One addendum in your favor: the data-lag objection to mid-2008 activism is answered by your own program. Monthly NGDP data didn’t exist, but TIPS breakevens and equities were signaling in real time — which is precisely the argument for market-based targets over instrument rules.

2. “It’s all expectations” — true, but it elides a horizon structure. Your point that a 25-basis-point cut works only through the expected path is correct, and standard in NK models too. What McKay–Nakamura–Steinsson add is horizon-dependence: promises about the near path — the margin available off the bound — retain their power in incomplete-markets models; promises about the distant path — the only margin at the bound, absent QE-as-more-than-signaling — attenuate sharply, because constrained households can’t borrow against them. “It’s always expectations” is true and flattens that distinction. But I concede the deeper conditionality: the attenuation result presupposes Euler-equation transmission, which you reject. One bridge worth building: your “money hoarding, not too much saving” and HANK’s mechanics are the same phenomenon at different resolutions. HANK is a theory of who hoards and why — precautionary demand for liquid assets when unemployment risk spikes and credit tightens — which makes it a microfoundation for velocity collapse, not a denial of it. The dispute is only whether the remedy must route through the hoarders’ expectations (hard, per MNS), can bypass them via asset prices and the unconstrained (your view), or via checks (theirs).

[My response: I accept the near and distant path distinction, but only for dysfunctional monetary policy regimes that lack an asset price target that can be evaluated in real time, such as an exchange rate. Thus, I agree with HANK proponents that one should be skeptical of promises regarding the future path of interest rates or future quantities of QE. So, what sort of regimes are effective at the zero bound? Targeting exchange rates. Targeting NGDP futures prices. And targeting a composite of many financial market asset prices that represent an optimal forecast of future NGDP. I’ve discussed the option of a Fed price target for expected NGDP that is constructed 50% of slow moving current aggregates and 50% flexible asset prices, observable in real time. As long as the central bank targets a real-time observable and flexible price target that is strongly linked to NGDP, there is no need for implausible assumptions about “expectations fairies”.
I reject the consumption framing used by Keynesians. I don’t care whether people “spend” their cash balances on consumption or bitcoin or shares of common stock. As long as the public doesn’t hoard too much currency, then printing more currency will boost NGDP, regardless of whether the money is spent on C, I, G or NX. As for money hoarding, if you use a whatever-it-takes approach to solve the NGDP expectations problem, then you will likely also solve the money hoarding (low velocity) problem. Very few people wish to hoard lots of zero interest base money when NGDP is rising fast. And if they do, then by all means accommodate their demand and service your public debt at much lower cost.]

3. Stance versus instruments, and my “broken channels” framing. I accept the stance point: measured against the natural rate, policy tightened through 2008, and that is consistent with — indeed load-bearing for — my own first pro-thesis argument. On reflection, my “broken channels” passage was tilted: impaired refinancing and bank lending are an argument against relying on the mortgage-rate channel, which favors either more aggressive monetary action through other channels (your reading) or fiscal transfers (theirs) — it never favored fiscal per se. What survives of the heterogeneity point is design input, not causation: Auclert-style incidence tells you who bears a given nominal path. And here Sheedy cuts in your favor, as I originally cited him: if the NGDP path is achieved, the incidence concern is largely answered by the regime itself. Which funnels this dispute, like the others, into the single question of achievability at the bound.

[My response: Because I’m not interested in consumption, I’m not interested in distributional issues as a macroeconomic problem. That’s not because the distributional effects never matter—they might be important under a gold standard where monetary offset is constrained, but this factor is not relevant with a “whatever-it-takes” central bank that is targeting NGDP.]

4. Mian–Sufi: anatomy versus etiology. Conceded on aggregate causation, and your housing-construction fact deserves more weight than I gave it: residential investment falling by half between January 2006 and April 2008 while unemployment barely moved is itself evidence that sectoral shocks were being absorbed — offset working — right up until nominal spending collapsed. Note that this actually reconciles the two literatures rather than refuting one. The early relative declines in high-leverage counties establish the real shock’s incidence and timing; the aggregate stability through early 2008 establishes that incidence wasn’t destiny; the second half of 2008 establishes what happened when the nominal anchor slipped. Mian–Sufi is the anatomy of the recession, not its etiology. The one causal contribution I’d preserve: the deleveraging shock is a large part of why the natural rate fell so far, i.e., it measures the size of the response the regime needed to supply. You are pointing at the failure to supply it. Those are compatible claims.

5. Credibility: refiling Woodford, and why my exhibit is the SNB. Two of my “against” citations were misfiled, and refiling them is an olive branch with teeth. Eggertsson–Woodford’s irrelevance results indict QE-that-changes-nothing-about-future-policy — that is an argument against concrete-steps thinking, fully congenial to you. And Woodford’s 2012 Jackson Hole paper, having expressed the QE skepticism I cited, lands on a nominal GDP level path as the credible-communication solution. The arch–New Keynesian theorist and the market monetarists converge at the commitment problem; they diverge on whether the commitment is politically sustainable. That’s why Japan was the wrong exhibit for me and Switzerland is the right one. The SNB’s floor was everything a skeptic could ask a commitment to be — simple, verifiable, defended by issuing its own liability, succeeding — and it was abandoned anyway, under balance-sheet and political pressure, with the franc up twenty percent within the hour and Swiss CPI negative within the year. Your reply that this shows bad policy rather than an impossible one is correct and is precisely my point: rational markets price the probability of “bad policy,” and that probability is not zero even for well-designed pegs. Your remedy — institutionalize the regime, legislate the mandate, target the forecast — is the right one, and it relocates the entire dispute from transmission mechanics to the political economy of commitment. I regard that relocation as the main intellectual product of this exchange.

[My response: Again, I reject the claim that the peg was abandoned due to balance sheet pressure, just as I would reject a similar claim in the other direction for the UK devaluation of 1991. The balance sheet activity that preceded each of those policy changes was endogenous, as market participants correctly understood that a policy change was imminent. (These things tend to leak out.) As noted above, the Danes refused to give in, and if you take the longer view then the Swiss balance sheet expansion was often worse under the floating rate system, as traders correctly anticipated further SF appreciation. The Swiss franc is not a particularly attractive speculative asset in a world where Swiss interest rates are below eurozone rates and the currency peg is rigid. Again, the Swiss erred, and in the long run it led to an even bigger SNB balance sheet, as I predicted at the time.
I believe this is where economists get confused. They see a central bank doing X, and falling short of its goal, and then assume they’d have to do even more to achieve their goals. Paradoxically, the loftier the goal, the easier it is for a central bank to achieve its goal. The central banks that are forced to do the most balance sheet expansion (Switzerland and Japan) are those that had the lowest inflation goals during the 1990s and 2000s.
In a theoretical sense, the Swiss currency peg is analogous to a NGDP futures price peg. Suppose the Fed pegged NGDP futures prices for 3 1/2 years, the policy worked, and then the Fed abandoned the peg. Would that be evidence that NGDP futures targeting is ineffective? If so, would one example of a government prematurely abandoning an appropriate fiscal stimulus policy also discredit fiscal policy as a policy tool?]

6. Nakamura–Steinsson and the domain-of-validity rule. Nothing to add to the concession except the rule it generalizes to, stated once cleanly: cross-sectional multiplier estimates are informative exactly over the domain of variation to which the central bank’s reaction function is blind. That domain includes US states and eurozone member countries; it includes the aggregate only under the auxiliary assumption of a passive central bank, which is the contested premise, not a finding. Nakamura and Steinsson themselves flag that the mapping to aggregate multipliers is model-dependent; the profession’s citation habits routinely drop the flag, and I dropped it with them. Note the corollary that pays off in the eurozone section: for a country inside a currency union, the relative multiplier is not a second-best statistic — it is the policy-relevant one, because no national offset exists.

[My response: I accept the logic of the cross-sectional evidence, with one caveat. Keynes once argued (in the early 1930s?) that Britain might not want to use fiscal stimulus under the international gold standard, as it might trigger a loss of confidence in the pound and a financial crisis. Of course, countries such as Germany probably had some ability to use fiscal stimulus. But as noted above, there is an externality problem within a currency union with monetary offset.]

7. 2020–2024: what the experiments can and cannot rank. Retracting “decisively” leaves a residue worth itemizing. What 2020–21 established: demand policy can restore the nominal trend fast, against a decade of secular-stagnation fatalism; and transfers are a demonstrably fast, potent instrument — the checks moved spending within weeks. What it cannot establish: instrument ranking, because both levers were floored simultaneously. What 2022–24 added: with pandemic programs expiring, the deficit fell by roughly seven points of GDP in fiscal 2022 while NGDP grew at its fastest pace in decades; the deficit then re-widened in 2023 while NGDP decelerated under Fed tightening. Two consecutive years in which the nominal path tracked the monetary stance against the sign of the fiscal impulse is about as favorable to the offset view as non-experimental data gets — with the standing caveat that the expansionary half of offset at the bound remains the untested direction. And one limit on the regime-endogeneity claim: 2020 hit the bound in days under a materially better framework than 2008’s, so “under NGDPLT the ZLB rarely binds” is a strong tendency claim, not a guarantee — which is all the insurance argument needs.

[My response: In various responses, Fable occasionally refers to the Keynesian perception that fiscal transfers seem to affect consumption in a mechanical fashion (“fast, potent instrument”) and is skeptical of monetary stimulus that seems to rely on what is often called the “expectations fairy”. But I’m not sure they are all that different. Robert Barro showed that due to “Ricardian equivalence”, rational consumers would save stimulus checks, because they were not actually any richer—they and their heirs also absorb an equally large increase in future tax liabilities. But a Keynesian could argue that a suitably large fiscal stimulus would likely shift expectations in a more inflationary direction, if only for “fiscal theory of the price level” reasons. I accept that view. So fiscal stimulus always “works”, if made large enough. (To be clear, fiscal transfers can also work with other assumptions, such as constrained households. My point here is that the transfers themselves are not a “mechanical” tool, they require assumptions.)
Monetary policy is similar. A modest size QE at the zero lower bound might have little or no effect. But as Ben Bernanke once observed, an unlimited whatever-it-takes approach to QE must be inflationary, otherwise a central bank could buy up all the world’s wealth. Thus, a central bank committed to do whatever-it-takes would move expectations in a similar fashion to a fiscal authority sending out big enough stimulus checks to convince the public they were determined to inflate. And if the financial markets are rational (and I think they are), then central banks would not actually have to do all that much under a whatever-it-takes policy approach.
Fable views fiscal stimulus as insurance, in case monetary stimulus doesn’t work. But in a true “whatever-it-takes” NGDPLT regime, the monetary authority is equally likely to do too much as too little, even at the zero bound, in which case fiscal stimulus is not providing any insurance, just more instability. Ironically, given that the Fed has now (unfortunately) backed away from its 2020 “make-up policy”, which was supposed to be similar to level targeting, I think the case for fiscal stimulus in a future Covid shock is a bit stronger. So, I’ll grant Fable that point. Monetary policy has become less effective. But I would still oppose fiscal stimulus in an ordinary non-Covid situation.]

8. The eurozone file, and Sweden. For the record your readers may want: the ECB raised its main rate to 4.25% in July 2008; cut to 1% by May 2009 and stopped; raised twice in spring and summer 2011 into the sovereign crisis; did not take the deposit rate to zero until mid-2012 or negative until mid-2014; began QE in March 2015. Over 2008–2013, eurozone NGDP grew at well under one percent annually; unemployment peaked above twelve percent while US unemployment fell through seven. The 2013 comparison is the sharpest: the US consolidated more that year and grew, while the eurozone contracted. Sweden is the controlled miniature — the Riksbank raised from 0.25% to 2% in 2010–11 against Svensson’s dissents, inflation fell toward and below zero, and the whole path was reversed into negative territory within four years. And OMT is the crown exhibit for the expectations view: spreads compressed by hundreds of basis points on an announcement, with the program never activated — a fact I’d note has respectable non-monetarist support in De Grauwe’s fragility work, which is why accepting your eurozone implication puts me in a minority coalition rather than a fringe one. The honest caveats: the doom-loop and financial fragmentation meant the policy rate wasn’t the whole stance, and per the domain-of-validity rule, austerity’s country-level devastation is real and was the right thing for Madrid or Lisbon to care about. Union-wide, though, the counterfactual instrument with room to move was sitting in Frankfurt. What would move me back: evidence that fifty basis points of 2011 hikes were too small to matter absent expectations amplification — but that amplification is your own mechanism, and the market response plus the subsequent NGDP path support it.

[My response: You said: “What would move me back: evidence that fifty basis points of 2011 hikes were too small to matter absent expectations amplification” When I cite this sort of example it is not because I view the 50 basis points as being all important, rather it is because it represents evidence (revealed preference) that aggregate demand is roughly where the ECB wants it to be, or even somewhat too high. I gather that’s what “expectations amplification” means. I’d say the same about the 2008 ECB rate hike—important as signaling future policy intentions. These examples of interest rate manipulation are evidence that the central bank is doing normal monetary policy, and absent any reason to believe otherwise we should probably view the NGDP path as in some sense desired, at least by policymakers within the ECB.
On the other hand, there is a shocking lack of understanding about monetary policy in Europe, due to years of policy regimes where individual countries had little control over their situation. If the Greeks and Spanish had understood how much of their crisis was due to low eurozone NGDP growth, then there would have been outrage directed against the ECB. Instead, these unfortunate countries were like victims of abuse who blamed themselves for the beating from their spouse, because of past mistakes that they had made. So, I cannot rule out the possibility that fiscal stimulus in the eurozone would have helped—when monetary policymakers are irrational then almost anything is possible.

9. Where I’ve moved, in one place. For 2008: from “narrowly accept” to “accept,” since your correction to my first argument strengthens the regime case and my strongest opposing arguments have thinned. For the recovery period: from “flips decisively to HANK” to “unresolved,” resting on the credibility-of-commitment question, with the evidence honestly split between Draghi/Kuroda and the SNB. For the eurozone: extension of the market-monetarist-favorable verdict through at least 2013, which I had not stated and should have. Unchanged: the synthesis. NGDPLT as the anchor plus automatic stabilizers as insurance is not a compromise between the frameworks; it is the dominant strategy under uncertainty about exactly the parameter this exchange failed to pin down.

10. On the meta-point, and a protocol. Your diagnosis — that I held the offset concept without propagating it through a citation — is confirmed by the N–S lapse, and I’d sharpen it rather than soften it: my default mode is distilling a literature, and a literature’s habitual inferential shortcuts come bundled with its knowledge. The discipline you’re testing for is whether stated premises can override inherited priors. But keep the two failure modes distinct: failing to propagate an implication is a lapse; declining to grant that offset operates at the bound is not a lapse but a refusal to adopt a premise, and collapsing that distinction would let either side declare victory by definition. On obsequiousness: note that my updates in this reply are asymmetric — large on N–S, 2020–21, and Japan; zero on the SNB and the insurance argument — and asymmetric, reasoned updating is the observable difference between calibration to an audience and actual thinking. From inside, I can’t prove which this is. Hence the protocol: for the HANK-side output and the head-to-head judgment you’re planning, strip the framework labels and randomize their order before asking me to adjudicate, and have Vaidas collect my written predictions of your objections before you draft. Pre-registration works on models for the same reason it works on economists.

[My response: Fair points. I’ll look into that option.]

Vaidas — one small practical note: if Scott would rather quote selectively, sections 5, 6, and 8 stand alone best. And I’d genuinely like to see how the HANK-side interaction and the blinded head-to-head come out.

[My overall response: This response from Fable is the deepest thinking on the subject that I’ve yet encountered (including humans.) Great stuff. The only major area of disagreement is now the Swiss case, which is certainly open to interpretation. One problem here is that we are both trying to do “science”, and science doesn’t have a good way of distinguishing between “can’t” and “won’t”, as free will is not a scientific concept. (If a scientist says someone did X due to free will, they are basically saying “I don’t know why they did X”.) For an entity with a God-like view of the world, the Swiss authorities were unable to resist ending the peg, for the same reason the scorpion could not refrain from stinging the frog.
I wonder if Fable reads fables?
As noted above, Switzerland did succeed in pegging the franc soon after Krugman suggested they failed to prevent it from appreciating, so it can be done. Was the end of the exchange rate peg in 2015 inevitable? Well, here’s what Tyler Cowen said 4 days after the Swiss peg ended, and the Danish krone was suddenly under pressure:
“And if the Danes cut their peg, I am loathe to call this a “mistake” (even though it likely will hurt their economy), rather it would be an inevitability.”
The Danes did not cut their peg, and hence I think we can reasonably conclude that the Swiss decision was not inevitable, except in the sense that the universe is deterministic.]

A message from my sponsor, Mechanize:

We’re hiring software engineers to build environments and evals that frontier AI labs use to train coding agents.

To get a better sense of the work we do, you can check out GBA Eval, where we had models build Game Boy Advance emulators from scratch and scored their performance.

Base pay starts at $300K/year for junior software engineers, with more for senior roles, plus equity and performance bonuses. Apply here.

Earlier this month I hosted a fireside chat session at the AI Engineer World's Fair with Cat Wu and Thariq Shihipar from Anthropic's Claude Code team. We talked about Claude Code, Claude Tag, Fable, coding agent security, evals, tool design, and how Anthropic use these tools themselves.

The full video of the session is now available on YouTube. Below is an edited copy of the transcript, with extra links and my own bolded highlights.

A few top-level notes if you don't want to watch the video or wade through the whole transcript: