The Harvard psychologist Steven Pinker is the high priest of rationalism. His 2018 book, Enlightenment Now, argued that liberal, rational, humanist values have made the world a better place. Bill Gates called it his “new favorite book of all time”. The same Whiggish, technocratic optimism was the force behind Pinker’s 2011 book, The Better Angels of Our Nature, which controversially claimed that violence and war are in a long decline.
Surprisingly, perhaps, for someone who used to write sparkling books on language and the mind, Pinker has also become a player in the culture wars. The subject of this book might seem innocent — a worthy attempt to rein in the madness of the post-truth era. Some, though, will perceive it as a provocation. Because in recent years rationality has been attacked as an imperialist project, soaked in the blood of the slave-owning Enlightenment heroes who first developed it, and deployed in the service of maintaining the social status quo. Or, as Pinker says, his opponents believe that “reason, truth and objectivity are social constructions that justify the privilege of dominant groups”.
Rationality, in other words, is not the patrimony of anyone with a human brain, and the only foundation of liberty and equality. In fact it is racist.
This book, then, is two things. On the face of it, and for perhaps 300 of its pages, it is an impassioned and zippy introduction to the tools of rational thought, covering logic, critical thinking, probability, statistics and game theory. Framing all that is a defence of reason itself, and a howl of anguish at the irrationality that sometimes seems on the verge of taking control.
Pinker’s ostensible target is conspiracy theorising. Two alarms went off in 2020, he warns. First there was the torrent of misinformation concerning Covid-19. The problem was not just outré claims about 5G networks or microchips. Even celebrated social scientists failed to understand the inexorable logic of exponential growth, which transformed the disease into a generation-defining public health crisis. The second “alarm” was the obfuscatory blizzard of claims about the legitimacy of the US presidential election. Everyone blamed social media, the “scapegoat for everything”, but what these alarms were really signalling, Pinker argues, was a crisis in rationality itself.
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Pinker’s real targets are not Trumpistas or antivaxers, though, they are his peers. He unpicks the many fallacies of logical argument, from the “straw man” to the “true Scotsman” fallacy. (No true Scotsman puts sugar in his porridge. Ah, but Angus does . . . Then Angus is not a true Scotsman.) Such fallacies “used to be treated as forehead-slapping blunders or dirty rotten tricks”, but are “becoming the coin of the realm” in academia and journalism.
Especially prevalent, he says, are the ad hominem, genetic and affective fallacies. An ad hominem argument targets the person. (Steven Pinker, for instance, says that rationality is universal, but he’s just another privileged white man.) The genetic fallacy attacks a belief’s origins. (Rationality must be racist because Enlightenment men were racists.) The affective fallacy appeals to emotion. (How can anyone say rationality is the answer while children are dying in poverty?)
Fallacy-spotting is something of a sport in the “rationality community”, which is one reason that rationalists can come across as patronising. (And they are not immune from fallacies themselves: Pinker certainly makes a straw man of his critics’ arguments.)
The many examples of when failures of rational thought are “punished by reality” are the more persuasive parts of the book. A technical chapter on Bayesian reasoning — which, broadly, is a way to update your assessment of the odds as new evidence emerges — gives the example of a medical diagnosis. Suppose 1 per cent of women get breast cancer, and that a test correctly identifies 90 per cent of positive cases, while giving false positives 9 per cent of the time. Now imagine a woman receives a positive test result. What is the chance she actually has the disease?
Doctors’ estimates range from 80 to 90 per cent. Which is very worrying when you discover that the real chance is 9 per cent. Unpicking all that requires a few pages — and a few equations — but it boils down to the fact that few of us, including doctors, are trained in probability, and we are so alert to the positive test result that we forget to factor in the overall likelihood in the population.
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This book offers further training in rationality as a life skill, and a tool of fairness. How game theory can protect the assets of a divorcing couple. (Tip: don’t hire expensive lawyers, arbitrate.) How the economic principle of expected utility can save you money on your house insurance. (Choose a higher excess payment.)
Alongside the seriousness is plenty of Pinker’s characteristic lecturer’s wit. He loves a cartoon and an illustrative joke. Unpicking the disjunctive syllogism in logic, more popularly known as the process of elimination, he tells the one about the logician Sidney Morgenbesser going to endless counselling sessions with his girlfriend. When the frustrated counsellor finally says, “Look, someone’s got to change,” Morgenbesser replies: “Well, I’m not going to change. And she’s not going to change. So you’re going to have to change.”
Ultimately Pinker wants us all to change. He wants the media, including social media, to incentivise truth-telling, not notoriety. He wants government policy to be built on evidence examined by panels of citizens — an excellent idea known as deliberative democracy. And he wants probability theory and psychological biases to be taught in schools and universities. “Rationality,” he says, “should be the fourth R.”
Punchy, funny and invigorating — albeit flirting dangerously with the construction of rationality as a political identity — this could be the textbook.
Rationality: What It Is, Why It Seems Scarce, Why It Matters by Steven Pinker
Allen Lane £25 pp412
