Every empirical claim, inspected.

What supports it

Sulfonamide antibacterials reached clinical use in 1935 and penicillin in the early 1940s. The first transatlantic telephone service (radio-based) opened in 1927 and the first cable service in 1956. Willis Carrier's electrical air conditioning dates to 1902, with residential installations following in the 1910s.

What is inference

None. The dates are documented. The only softness is that air conditioning arrives two years after 1900 — the sentence is true as written and would be false if it said 1905.

What would weaken it

A documented pre-1900 clinical antibacterial, transoceanic voice link, or mechanical domestic cooling system available for purchase.

Sources

• Secondary Fleming, Chain, Florey — Nobel Prize in Physiology or Medicine 1945 Nobel Foundation, prize citation and lectures, 1945
• Secondary History of transatlantic telephony AT&T archives: 1927 radiotelephone service; TAT-1 cable, 1956
• Secondary Willis H. Carrier, "Apparatus for Treating Air" US Patent 808,897, filed 1904, granted 1906; first system installed 1902

What supports it

The European Recovery Program disbursed roughly $13 billion between 1948 and 1952. Marshall's 1947 Harvard address framed it as directed "against hunger, poverty, desperation and chaos," and the Truman administration argued it to Congress on containment and trade grounds. The framing as self-interest is documented in the primary record.

What is inference

The book's stronger reading — that the plan caused the recovery and so proves cooperation pays — is the part that is argued. Historians disagree on the size of the economic effect: some credit institutions and confidence more than the money itself; others find the direct contribution modest against Europe's own output.

What would weaken it

Evidence that the funded economies would have recovered as fast without the program, or that the program was in fact argued to Congress primarily as charity.

Sources

• Primary George C. Marshall, address at Harvard University 5 June 1947, Department of State Bulletin
• Secondary DeLong & Eichengreen, "The Marshall Plan: History's Most Successful Structural Adjustment Program" NBER Working Paper 3899, 1991
• Secondary Alan Milward, The Reconstruction of Western Europe 1945–51 Methuen, 1984 — the skeptical reading

What supports it

The Costs of War project at Brown University estimates US spending on the Afghanistan and Pakistan war zone at roughly $2.3 trillion through 2021, before interest and veterans' care. Aid and reconstruction spending across the same period was a small fraction of that.

What is inference

The counterfactual — what an earlier stabilization would have cost, and whether it would have worked — is inference. The cost of the collapse is documented; the cost of the road not taken is an estimate the book is making, and it should be read as one.

What would weaken it

A credible estimate that earlier stabilization would have cost as much as the war did, or evidence that stabilization was attempted at scale and failed for reasons money could not fix.

Sources

• Primary Costs of War project, "U.S. Costs to Date for the War in Afghanistan" Watson Institute, Brown University, 2021
• Primary Special Inspector General for Afghanistan Reconstruction, "What We Need to Learn" SIGAR lessons-learned report, August 2021

What supports it

Great Britain won one Olympic cycling gold between 1908 and 1992. At Beijing 2008 the team won eight of the ten track cycling golds and fourteen cycling medals in total. Performance director Dave Brailsford publicly attributed the turnaround to "the aggregation of marginal gains."

What is inference

That marginal gains caused the result is the argued part. National Lottery funding from 1997, talent identification, and full-time coaching arrived in the same decade; disentangling their contributions from the small-factor philosophy is not possible from the public record. The book uses the story as an illustration of the principle, not as proof of it.

What would weaken it

Evidence that the medal haul tracks funding and athlete pool size closely enough that the marginal-gains programme added nothing measurable.

Sources

• Primary International Olympic Committee, Beijing 2008 cycling results Official results database
• Secondary Dave Brailsford interviews on marginal gains BBC Sport, 2012

What supports it

The bat-and-ball item is from Frederick's Cognitive Reflection Test, on which most respondents at elite universities answer "ten cents." The two-system account is Kahneman's synthesis of decades of judgment research; the "fluency" finding — that ease of processing raises judged truth — is replicated across many labs.

What is inference

The "two systems" are a description, not two organs; Kahneman himself calls them a useful fiction. The book's further claim that the fast mode is built from what was once slow — that training is what installs it — is well supported for skill acquisition and is inference when applied to values.

What would weaken it

Failure to replicate the fluency-truth effect, or evidence that reflective and intuitive answers do not dissociate in the way the CRT measures.

Sources

• Primary Shane Frederick, "Cognitive Reflection and Decision Making" Journal of Economic Perspectives 19(4), 2005, doi:10.1257/089533005775196732
• Secondary Daniel Kahneman, Thinking, Fast and Slow Farrar, Straus and Giroux, 2011

What supports it

Baumeister and colleagues' review found negative events, feedback, and information weighted more heavily than positive equivalents across relationships, learning, memory, and impression formation. Hedonic adaptation — the re-zeroing of gains — is documented from lottery winners to the newly disabled.

What is inference

The book's calibration — that gratitude is "accurate thinking, not positive thinking" — is a prescription derived from the bias, not a finding. Gratitude interventions show modest, real effects on wellbeing in trials; "accurate" is the book's framing.

What would weaken it

A body of work showing symmetric weighting of gains and losses in attention and memory once arousal is controlled for.

Sources

• Primary Baumeister, Bratslavsky, Finkenauer & Vohs, "Bad Is Stronger Than Good" Review of General Psychology 5(4), 2001, doi:10.1037/1089-2680.5.4.323
• Primary Brickman, Coates & Janoff-Bulman, "Lottery Winners and Accident Victims" Journal of Personality and Social Psychology 36(8), 1978

What supports it

Redelmeier and Kahneman found colonoscopy patients' retrospective ratings tracked the peak and the final moments of pain rather than its duration — the peak-end rule and duration neglect. Later choices followed the memory, not the experience.

What is inference

The "two selves" are a metaphor for two measurement methods (moment-to-moment versus retrospective). The book's advice to "rig the triggers" rather than referee the two is its own extension of the finding.

What would weaken it

Replications in which remembered utility tracks total experienced utility once duration is made salient.

Sources

• Primary Redelmeier & Kahneman, "Patients' memories of painful medical treatments" Pain 66(1), 1996, doi:10.1016/0304-3959(96)02994-6

What supports it

Prospect theory's value function is steeper for losses than gains; Tversky and Kahneman's 1992 estimate of the loss-aversion coefficient was about 2.25. The endowment effect — valuing what you hold above what you would pay for it — is the same asymmetry seen from the other side.

What is inference

The ratio varies by domain, stake size, and population, and some researchers argue the effect is smaller and more context-dependent than the textbook figure. "About double" is a fair summary of the classic estimate, not a constant of nature.

What would weaken it

Meta-analytic evidence that loss aversion disappears at small stakes or in experienced traders — some of which already exists and is why this is not marked high.

Sources

• Primary Kahneman & Tversky, "Prospect Theory: An Analysis of Decision under Risk" Econometrica 47(2), 1979, doi:10.2307/1914185
• Primary Tversky & Kahneman, "Advances in Prospect Theory" Journal of Risk and Uncertainty 5, 1992
• Secondary Gal & Rucker, "The Loss of Loss Aversion" Journal of Consumer Psychology 28(3), 2018 — the critical reading

What supports it

Small, Loewenstein and Slovic found donations to an identified child exceeded donations to statistical victims, and that presenting statistics alongside the child reduced giving. Slovic's review documents "psychic numbing": compassion that fails to scale with the number of lives at stake.

What is inference

The book's calibration — "translate in both directions" — is prescription. The finding itself is among the more robust in the field.

What would weaken it

Evidence that willingness to help scales linearly with number of victims once framing is controlled.

Sources

• Primary Small, Loewenstein & Slovic, "Sympathy and callousness" Organizational Behavior and Human Decision Processes 102(2), 2007, doi:10.1016/j.obhdp.2006.01.005
• Primary Paul Slovic, "If I look at the mass I will never act" Judgment and Decision Making 2(2), 2007

What supports it

Survivorship bias is a standard statistical selection problem. The usual illustration — Abraham Wald advising that returning aircraft be armoured where they were not hit — is grounded in Wald's wartime memoranda for the Statistical Research Group.

What is inference

The popular retelling of the Wald story is embellished; the memoranda are about estimating vulnerability from damage on survivors, and the "armour the clean spots" line is a later gloss. The bias is real regardless of the anecdote.

What would weaken it

Nothing weakens the bias itself; the anecdote would be weakened by evidence Wald never made the recommendation attributed to him.

Sources

• Primary Abraham Wald, "A Method of Estimating Plane Vulnerability Based on Damage of Survivors" Statistical Research Group memoranda, 1943; reprinted as CRC Report 432, 1980
• Secondary Marc Mangel & Francisco Samaniego, "Abraham Wald's Work on Aircraft Survivability" Journal of the American Statistical Association 79(386), 1984

What supports it

Axelrod's computer tournaments of the iterated prisoner's dilemma were won by Tit for Tat — cooperate first, then mirror. His analysis identified niceness, retaliation, forgiveness, and clarity as the properties of successful strategies. Later work showed strictly mirroring strategies lock into feuds after noise, and that forgiving variants do better when errors occur.

What is inference

Tournaments are models; that their winners describe how human societies actually build trust is the book's inference, supported by field studies of reciprocity but not proven by the game.

What would weaken it

Tournament or field evidence that unconditional defection or unconditional cooperation outperforms conditional strategies under realistic noise.

Sources

• Primary Robert Axelrod, The Evolution of Cooperation Basic Books, 1984
• Primary Nowak & Sigmund, "Tit for tat in heterogeneous populations" Nature 355, 1992 — generous tit for tat under noise

What supports it

John Calhoun's enclosures, culminating in "Universe 25," gave mice unlimited food, water, and nesting with no predators; population peaked, social behaviour broke down, and the colony went extinct. The experiments are thoroughly documented.

What is inference

The extrapolation to human societies is disputed by historians of science, who note the enclosures removed dispersal and the results were read through the overpopulation anxieties of the 1960s. The book's answer — that a sealed paradise was tested, not paradise — is a reading, offered as one; the book itself calls this the best evidence any objection in it holds.

What would weaken it

Evidence that populations with open frontiers and unlimited roles show the same behavioural sink, or that human abundance produces the same collapse independent of confinement.

Sources

• Primary John B. Calhoun, "Population Density and Social Pathology" Scientific American 206(2), 1962
• Primary John B. Calhoun, "Death Squared: The Explosive Growth and Demise of a Mouse Population" Proceedings of the Royal Society of Medicine 66(1), 1973
• Secondary Ramsden & Adams, "Escaping the Laboratory: The Rodent Experiments of John B. Calhoun" Journal of Social History 42(3), 2009 — the critical reading

What supports it

A 2016 analysis in The Lancet Psychiatry estimated that scaling up treatment for depression and anxiety in 36 countries would return about four dollars in improved health and productivity for every dollar spent.

What is inference

The figure is a model estimate, sensitive to assumptions about treatment coverage and productivity valuation. The direction — untreated illness costs more than treatment — is widely supported; the ratio is the modelled part.

What would weaken it

Real-world scale-up programmes whose measured returns fall well below the modelled figure, or below one.

Sources

• Primary Chisholm et al., "Scaling-up treatment of depression and anxiety: a global return on investment analysis" The Lancet Psychiatry 3(5), 2016, doi:10.1016/S2215-0366(16)30024-4

What supports it

Finland's 2017–18 trial found no meaningful reduction in employment and improved wellbeing among recipients. Manitoba's Mincome experiment (1974–79) found small work reductions concentrated among new mothers and students, alongside fewer hospitalizations. Cash-transfer trials in Kenya and Stockton report similar patterns on employment.

What is inference

Every trial to date is time-limited, small, or targeted; none tests a permanent, universal, nationally funded floor. Effects on prices, migration, and long-run labour supply at full scale are unknown. The book states the level as owned by the vote for exactly this reason.

What would weaken it

A large, long-duration, universal trial showing significant labour withdrawal or price inflation that erodes the floor — the falsifier the book names as "floors reliably destroying the contribution they protect."

Sources

• Primary Kangas et al., "Evaluation of the Finnish Basic Income Experiment" Finnish Ministry of Social Affairs and Health, 2020
• Primary Evelyn Forget, "The Town with No Poverty" Canadian Public Policy 37(3), 2011
• Primary Haushofer & Shapiro, "The Short-term Impact of Unconditional Cash Transfers to the Poor" Quarterly Journal of Economics 131(4), 2016