Sam Enright works on innovation policy at Progress Ireland, an independent policy think tank in Dublin, and runs a publication called The Fitzwilliam. Most relevant to us, on his personal blog, he writes a popular link roundup; what follows is an abridged version of his and Links for April.
Blogs and short links
1. Rest in peace to Robert Skidelsky. Alas, I only read the abridged version of his three volumes on Keynes, which are difficult to find in paperback. Someone ought to do a reprint. Here’s a passage from Skidelsky’s Money and Government (2018):
Ronald Coase recalled the English economist Ely Devons saying to him, ‘If economists wished to study the horse, they wouldn’t go and look at horses. They’d sit in their studies and say to themselves, “What should I do if I were a horse?” And they would soon discover that they would maximise their utilities.’ This joke gives a profound insight into the economic method.
I found that quote when reading about what Rebecca Lowe has been reading. The first piece in that roundup is this essay by T.S. Eliot about literary criticism. She read it for a mini-conference on Eliot in St. Louis, Missouri, hosted by Sebastian Garren and inspired (I’m proud to say) by the Fitzwilliam Milton Friedman conference. I’m not a frequent user of emoji, but: 🥹
2. David Friedman responds to my essay about his dad. Every source I looked at (biographies, Wikipedia, The New Yorker) said that Milton Friedman was 5 feet nothing. David says his dad was 5’3”, and I am in no place to argue. What’s going on here? There are so many photos of Milton next to other people of known height, and three inches is not small. This seems like a big error to me. Also, for people who said I was being too mean in my original post, I only mentioned Milton Friedman’s height because it genuinely seems like he got a kick out of being short. I respect all short kings.
3. Gavin Leech on the state of Chinese AI. He concluded that they are a year behind the West, but the post was in November 2025, and he says it’s outdated by now. Still worth reading for (among other things) discussion of how China ‘distils’ knowledge about frontier models from the open internet.
4. Nicholas Decker makes the case that Steven Berry, Jerry Hausman, and Ariel Pakes should have won the Nobel Prize in economics. Read also for some intuition for the Hausman test between fixed and random effects estimation in panel data, which went over my head as an undergraduate.
5. Stephen Malina’s links. My favourite entry here is Afra Wang’s on the story of a Beijing vibe coder. The fact that this quote comes from someone named Liu Xiaopai is a point in favour of Dan Wang’s “no two peoples are more alike” thesis about Americans and Chinese:
6. An archive of all the books mentioned on the Conversations with Tyler podcast.
7. Shruti Rajagopalan on Delhi’s recent AI Summit. Shruti’s Substack and podcast are indispensable.
Music and podcasts
1. Tyler Cowen and Alex Tabarrok on the history of options pricing. I am struck by the history of polymath (usually French) economists whose work was so advanced that (usually Anglo) economists didn’t have the mathematical background to understand it for decades or more. Augustin Cournot was applying the concept of Nash equilibrium in the 1830s. Louis Bachelier derived the equations for Brownian motion five years before Einstein independently rediscovered them, and had worked out the core conceptual framework of Black-Scholes theory over seventy years earlier.
2. Joe Studwell on African economic development. I still haven’t read How Africa Works, but I look forward to doing so; perhaps we’ll do an African economic development edition of the reading group.
3. Rebecca Lowe and Tyler Cowen on the definition of freedom. This podcast has a fun format: the host and guest discuss a philosophically laden word, for the purposes of reaching a ‘working definition’ of it. If I were ever on such a podcast, ‘alignment’ or ‘causality’ would be fun topics.
4. Talking Heads, Speaking in Tongues. Moon Rocks is my favourite track here, while This Must Be the Place is less interesting to me. Interestingly, Brian Eno was not the producer on this album after having been it for the previous three. I gather there was some drama because he was leaving an increasingly large footprint.
5. The Clash, Combat Rock. There is wisdom to the critical consensus that this album is weaker than either London Calling or The Clash. Rock the Casbah is mighty, and I suppose now is as fitting a time as any for satires of decrees by Ayatollah Khomeini. I also learned that Straight to Hell is the Vietnam protest song sampled on Paper Planes, very cool.
6. Mingus Big Band, The Charles Mingus Centennial Session. I love Charles Mingus; the Mingus Big Band is an ensemble started by his widow over a decade after he died. The opening performance of Work Song (Break the Chains) is very strong, which, confusingly, is completely separate from the Nat Adderley jazz standard. You may be interested to know that the trombonist on this album is internet public intellectual Coleman Hughes. What’s the correct lesson to infer from the fact that successful people were so frequently highly successful in some unrelated area?
Books and Papers
1. Dave Donaldson, Railroads of the Raj: Estimating the Impact of Transportation Infrastructure. Genuinely one of the most incredible economics papers of our time; here is Kevin Bryan on why Dave Donaldson’s John Bates Clark Medal was well deserved. This also made it to Nicholas Decker’s list of 11 favourite economics papers. Donaldson wrote this paper as part of his PhD, which took him eight years. The main reason it took him so long is that it involved manually (!) digitising 1.5 million (!!) data points from (largely handwritten) colonial archives (!!!). From that data, he was able to identify transportation costs in British India by looking at local variations in salt prices whose origin is known. Salt is an incredibly homogeneous good; if you know how much a particular type cost in Madras, and how much it cost in Mumbai, then you also know how much it cost to transport. From this, Donaldson is able to estimate a parameter θ, the elasticity of the volume of trade with respect to price. By combining this information with an off-the-shelf general equilibrium model of trade, he is able to get a precise estimate for the welfare effect of railroad expansion under the Raj.
This is extremely clever, but the issue is that railroad placement is still endogenous: it could be that railways were only built in growing areas, which would have done well anyway. What would be more convincing is if we could show that sites that were equally good candidates for railroads, that were never built for idiosyncratic reasons, did not share in the benefits. This is how Donaldson uses the Kennedy plan (1848) and the Lawrence plan (1869) for railroad expansion in India. This is an instance of a placebo test, a confusingly named piece of causal inference apparatus that has little to do with the term’s use in psychology. This is probably the least convincing part of the paper, because it could always be that the planned lines were cancelled for some other reason, which would also have caused those regions to have lower incomes subsequently.
2. Dave Donaldson, Richard Hornbeck, Railroads and American Economic Growth: A “Market Access” Approach. This paper is largely a revision of Robert Fogel’s classic 1964 study of railroads in American economic history, which argued that they were not indispensable for growth in the 19th century. He used a methodology called “social savings”, in which you take the quantity of good transported by a new technology, and then calculate what it would have cost to transport with the next-best available technology. Fogel argued there was a surprisingly high degree of substitutability between railroads and canals and other forms of transport. He concluded that the absence of railroads in 1890 would have reduced GNP by 2.7%, far below what most economists at the time would have expected.
3. Tyler Cowen, The Marginal Revolution: Rise and Decline, and the Pending AI Revolution. This is more of a monograph than a book, which you can read for free here. I still haven’t figured out how to use Tyler’s AI integration in a way that is more fruitful than just uploading the EPUB to Claude and asking questions.
The first part of The Marginal Revolution is an intellectual history of the ‘marginal revolution’ of 1870s economics, as led by William Stanley Jevons, Léon Walras, and Carl Menger. The Hollis Robbins review provides a good summary:
Chapter three is about why, despite being quite obvious today, it took so long for marginalism to develop. He analogises economics to geology and evolutionary biology, as fields that are also conceptually simple but historically slow-moving. He also makes a sociological claim about how, since any professional economist worth their salt understood marginalism, competition was pushed into more technical domains, like the use of econometrics and more careful empirical work.
There’s also some good stuff about the precursors to marginalism, such as Jules Dupuit. Many of the ideas of marginalism were also independently discovered by the Irish polymath Dionysius Lardner in a book about railway economics (!!!) in 1850. I literally cannot believe this never came up at our Irish railway economics event. If any of you would write about this guy for The Fitzwilliam, please email me! This was also an amazing detail (page 43):
As is often the case with Tyler, it’s hard to tell what he’s actually trying to say in this book. Here’s what I picked up: The ‘marginal revolution’ made the economy feel much more understandable and intuitive than it actually is. Sophisticated economic theory sometimes works for a while, but then it loses its predictive value. The most influential asset pricing model of the 20th century, the capital asset pricing model (CAPM), has a key parameter β, the sensitivity of an asset to movements in the market portfolio. We know from a literature culminating in Fama and French (1992) that β doesn’t actually predict anything. And nowadays, the best-performing financial models are machine learning algorithms that pick up on statistical patterns and have almost no actual theory baked into them.
There are two possible reasons for this:
CAPM was always wrong.
CAPM was an accurate description of the world in the past, but it no longer is.
It’s a little from column A, a little from column B. Artificial intelligence reveals that our prior state of “understanding” was thinner than we thought. But also, contrary to the pessimists, economics is a real discipline that has aided our understanding of at least some topics. It could just be that the world has gotten genuinely less interpretable over time.
Marginalism is partly just a set of mathematical identities about first-order conditions and optimisation. Tyler calls this “tautological marginalism”. “Intuitive marginalism” is the idea that these tautologies are actually important, and that the idea of reasoning “at the margin” is useful for many applications, such as in Jevons paradox. Although humans’ intuitive marginalism might lose its force in explaining the world, Tyler says that it will survive in the form of the weights of future models (page 119):
The training of Large Language Models (and other forms of AI) will enshrine marginalism into their basic operating concepts, as those models are trained on writings that understand marginalist concepts… marginalism will not die, but we will automate it.
The Straussian reading of this monograph is that Tyler is grappling with what it’s like to be an economist in his mid-sixties today, having watched software eat the world, including his life’s work. All my economist friends now wish that they had studied maths or computer science as undergraduates. Economics has had various intellectual edifices come and go, either because the theory was wrong all along, or because it only explained a narrow range of phenomena during a certain time period. That includes schools Tyler has a soft spot for, like Chicago price theory and Mason public choice theory. His melancholy is most evident on page 106:
Sadly, price theory is fading in relevance, and it is taking marginalism down with it. It used to be that some graduate programs favored the axiomatized approach to micro and others (e.g., University of Chicago, UCLA, University of Virginia) favored the price theory approach. These days the axiomatizations have won out pretty much everywhere, except at my own George Mason University.
Finally, some fun tidbits: on whether economics is too mathematical, we have this quote from Shengwu Li;
“Can you give me an economic intuition for that result?” means “Can you explain that using math that was introduced to economics >20 years ago?”
Corollary: Topkis’ theorem counts as economic intuition. Also virtual values. And eigenvalues.
Abortions are surprisingly elastic (page 31):
We find that a hundred-mile increase in distance to the nearest [abortion] clinic is associated with 25 percent fewer abortions.
In the latest edition of “economists have predicted nine out of the last five recessions”, I was unaware that there was a sunspot theory of macroeconomics (page 59):
“[William Stanley] Jevons’s obsession with the average also showed up in his macroeconomic work on the “sunspots” theory of commercial cycles. Jevons had presented evidence that business cycles occur at a typical regularity of about ten and a half years. At the same time, astronomers had told him that the solar period had a typical regularity of about ten and a half years. He concluded that the two phenomena were related, but never successfully pinned down the evidence or the case for a causal relationship.”
I pronounce William Whewell (p. 103) as Victorian polymath of the month:
“Alfred Lord Tennyson called him “a lion-like man.” [William] Whewell was a legitimate polymath, making contributions to mechanics, physics, geology, astronomy, mathematics, economics, and also poetry. He was an Anglican priest, he translated works by Goethe and Grotius, and he organized a pathbreaking citizen science project to study ocean tides. It was he who persuaded Darwin to become secretary of the Geological Society of London, noting […] that geology was a critical input into Darwin’s theory of evolution. On science and its philosophy, Whewell’s major work was his 1837 multi-volume History of the Inductive Sciences, from their Earliest to the Present Times, now largely forgotten outside of academic history of science, but massively influential in his time. Whewell also coined the terms scientist (in 1833), physicist, linguistics, consilience, catastrophism, uniformitarianism, and astigmatism, an impressive list. To Michael Faraday he suggested the terms anode, cathode, and ion.”
Films and videos
1. Tom Moore, Nora Twomey, The Secret of Kells. An absolutely gorgeous animated children’s film about the creation of the Book of Kells. According to legend, the manuscript was started on the island of Iona by St. Colmcille, before being brought to Kells in County Meath in the 9th century. This was the first film in a thematic Celtic mythology trilogy, which I watched because I liked the third one, Wolfwalkers, so much. Eventually, I would like to pen something longer about Irish cinema, which has had many great entries. A strength is that, owing to our sentimentality, internationally acclaimed actors will work (presumably for much less money) on local projects, e.g., Brendan Gleeson voices the Abbot of Kells here.
Endnotes:
[1] One of the reasons why Bachelier didn’t get very far is that his thesis advisor, a fellow by the name of Henri Poincaré, wasn’t very impressed with him. The story goes that Leonard Savage (he of the Savage axioms) sent a postcard raving about Bachelier to Paul Samuelson, who then told Fisher Black and Myron Scholes and Robert Merton. There’s a lot of alpha in sending postcards!
[2] Lore: Charles and Sue Mingus’s unofficial marriage ceremony was “officiated” by the poet Allen Ginsberg.
[3] If I’ve understood correctly, he plays on tracks 1, 2, 9, and 11.
[4] The timelines on the publication of top-five economics journal articles have stretched to a point of beggaring belief. ‘Railroads of the Raj’ was circulating as a working paper since 2010, but wasn’t published in the American Economic Review until 2018, which was 17 years after the project began. This was a year after Donaldson won the John Bates Clark medal, partly for the strength of this paper.
[5] There’s not tons of information about this online. There is a webpage about expansion under the Raj on the Indian government’s railways webpage, but as befits my previous experience with Indian trains, it’s broken.
[6] There’s some pretty interesting stuff (to me) about Jevons’ work on how to construct price indices, and why he favoured the geometric mean over the arithmetic mean for this purpose. See page 58.
