September 27, 2021   6 mins

For thirty years, the eminent linguist Steven Pinker has been writing a series of popular science books that alternate, title by title, between deep dives into abstruse aspects of cognition and broader ruminations on matters of grand social importance. 1999’s Words and Rules: The Ingredients of Language, is in the former category, while 2002’s The Blank Slate: The Modern Denial of Human Nature is in the latter. Where Words and Rules had tightly-written chapters on irregular verbs, The Blank Slate reflected languidly upon broad matters of public policy, informed by a substrate of evolutionary psychology.

Now, in Rationality: What It Is, Why It Seems Scarce, Why It Matters, Pinker synthesises both aspects of his oeuvre. On the one hand, Rationality briskly introduces you to essential concepts like Bayesian reasoning and technical terms like modus ponens. But the technical, learned aspects of the book are accompanied by a polemical drive. Rationality matters — every day, everywhere. Especially at present, in a world that many think has gone mad, whipsawed irrationally by social media mobs and online conspiracy theories. Pinker argues that methods of rationality represent not an esoteric corner of cognitive science or philosophy, but an essential set of tools for individual human flourishing, maintaining our sanity and perpetuating civilisation as a collective whole. To reason and think clearly is to be modern, and even requisite in order to be moral.

In the wake of the financial crisis of 2008, the rational actor and “homo economicus” seemed to have failed us. Nature abhors a vacuum, so there was a vogue for the field of behavioural economics, a discipline that operates in the gray zone of economic frictions and psychological irrationalities powered by faulty intuition. A crop of authors harvested these ideas: Dan Ariely, Rom Brafman, Ori Brafman, Cass Sunstein, and Richard Thaler among them. More broadly, Daniel Kahneman and Amos Tversky’s heuristics and biases research program, to which all these authors owe a debt, entered the mainstream — Kahneman also contributed a bestseller, Thinking, Fast and Slow in 2011. Barack Obama’s administration tried to ‘nudge’ America through policy. David Cameron’s government, and the British civil service, embraced nudging too.

Rationality is part of a tacit backlash against these authors, their books, and the atmosphere they generated in public policy circles in the 2010s.

Today, Dan Ariely faces accusations of fraud at worst and scientific malpractice at best. More broadly, behavioural economics has been hit by the replication crisis. Humans respond to incentives, and for scientists, sexy and vivid results are rewarded, while negative findings can stall a career. The scientific culture of the aughts was defined at its peril by “publish or perish,” as well as sloppy experimental practices, a mechanically unthinking application of statistics, and cognitive biases in the very fields dedicated to understanding how rationality fails us. Kahneman himself began having doubts in 2012, justifiably, about some of the results reported in his 2011 book.

Pinker’s good news in Rationality is that with deliberate effort, humans can think clearly and move beyond their biases. Where much of cognitive psychology focuses on illusions and mental misfires, Rationality instead argues that our faculties are up to the task, and that this is all a natural consequence of our evolution. Evolutionary psychology leans heavily on the idea that humans are only equipped with “stone-age minds” in a technologically advanced present. Pinker seems a bit chagrined at this angle being so overplayed, and in Rationality he attempts to redress the balance, making the case that humans are naturally equipped to reason and that reason is not a dark art or the province of philosophers and mathematicians alone.

If you are a consumer of anthropology and ethnography or even have simply watched The Gods Must Be Crazy, you are aware of the preternatural skills of the San hunters of the Kalahari desert. Pinker shows this is not due to inborn traits, but the ability of the San to take in the information around them, the time of the year, the season, the species of antelope, and make inferences in alignment with their overall goals. The San, like all humans, engage in a rough and ready form of syllogistic reasoning. They start with axioms, premises informed by their experiences, and deduce logical consequences from their assumptions. Things don’t just “happen” in the Kalahari, there is a rhythm and rhyme the hunters exploit, a pattern and sense of the world that allows them to survive and flourish. Steenbok antelope are hunted during the rainy season while eland are stalked during the dry season. You might think this is due to custom and tradition, but the San are aware that steenbok has stiff joints during the rainy season while eland hooves are ill-equipped to navigate sandy soil. They hunt animals in the season that loads the dice for a success hunt. The alternative, simply, is a higher risk of starvation. The San have goals, and they naturally use the tools of rationality to achieve them.

But what if the San did not rationally know the reasons for their actions?

One of the essential points in Rationality is that reasoning and understanding the world are collective enterprises. We know that socially-generated knowledge and rationality can be embedded enduringly through rules and taboos. Yes, those executing a cultural script may not be aware of the ultimate reasons, but a deeper investigation by anthropologists can reveal that mindless traditions actually serve functional purposes.

Joe Henrich in 2015’s The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter reports how traditional societies across the world have a system of preparing cassava that prevents them from getting cyanide poisoning. Those following the methods do not know what cyanide is, nor do they even know that consuming unprepared cassava will lead to death, but their culture comes preloaded with the fruits of adaptive learning that are highly rational.

The deepest insight then is that our ability to reason through complex problems depends on our willingness to stand on the shoulders of giants. Though we can all reason, Pinker does not shy away from conventional pitfalls of human analysis such as the Monty Hall problem, the gambler’s fallacy and the base rate fallacy. He recounts that Paul Erdos, author of 1,500 mathematical papers, was as mystified by the Monty Hall problem as most people who encounter it. He refused to believe he was wrong, relying on his native intuitions, despite his prodigious ability to work through formal mathematics.

The point is that the most brilliant individual mind can fail at reasoning unless it approaches the enterprise with humility and the willingness to update beliefs and understanding. The scholarship reviewed in Rationality, from Aristotle to machine learning, is not just the product of singularly brilliant minds, but the collective efforts of whole scientific traditions. The replication crisis shows that groups of scholars can blunder into traps and dead ends en masse. But advances in fields like statistical decision theory would be impossible without the collective efforts of disparate research groups across numerous domains. Pinker’s treatment of deep learning neural networks also makes it clear that some of these tools for rationality are approaching the dark edge of Arthur C. Clarke’s formulation that “any sufficiently advanced technology is indistinguishable from magic.” And, like magic, they often fail without the guiding hand of human reasoning faculties.

Rationality, Pinker says, was partly in response to students at Harvard finding the world puzzling, especially with much of psychology focused on how human rationality fails. If Pinker makes the case for thinking clearly, with the most powerful tools we have, whether it be 21st-century computational methods in machine learning or sharper formal analysis that draws upon mid-20th-century economic game theory, he still remains fully aware that he lives in an empirical world of irrationality.

Pinker was not one of the ‘Four Horsemen’ of New Atheism: Christopher Hitchens, Richard Dawkins, Daniel Dennett and Sam Harris. But he is, and long has been, a fellow traveller of the group (he is also personally close to Dawkins). In the early 2000’s he took equal-opportunity aim at the Right’s attachment to traditional religion in The Blank Slate while taking the Left to task for its denial of human nature. Twenty years later, he made an extended call for a revival of the cult of rationality in Enlightenment Now. Pinker’s enthusiasm for applying rationality and empiricism to the world reflects the intellectual culture of the mid-2000’s when Dawkins was riding high with his critiques of evangelical Christianity and public intellectuals were gathering to celebrate the Enlightenment in conferences like Beyond Belief. The familiar flame of this hopeful past burns bright throughout Rationality.

But ours today is a world of cancel culture and QAnon. Ideological polarisation that has turned the pandemic into the object of a culture war in the United States. Pinker does address the reality that the world today is not the world he might have imagined it would be a generation ago, as irrationalities and superstitions spread like ideological pandemics on social media.

The vision of the aughts was one of a reason-ruled future, but Rationality was written in the wake of Donald Trump, whose rise and popularity as an emotive demagogue triggered a reactionary flare-up of identity politics on the cultural Left. This is the world where David Hume observed that “Reason is, and ought only to be the slave of the passions”. To a great extent, the project of making Bayesian reasoning, game theory and machine learning accessible and palatable to the public seems born of the disappointments of the past generation. If you are a deep reader of Scott Alexander’s Slate Star Codex, Rationality may not offer you much new food for thought. But if you are terrified by the insanities of the present, and wish to replenish your intellectual armoury in the fight for progress and reason in the 21st century, then Rationality is what you will want to bring to the battlefield.

Razib Khan is a geneticist. He has written for The New York Times, India Today and Quillette, and runs two weblogs, Gene Expression and Brown Pundits. His newsletter is Razib Khan’s Unsupervised Learning