Rationality. By Steven Pinker. Viking; 432 pages; $ 32. Allen Lane; £ 25

STEVEN PINKER is too honest to deny that he risks blowing in his own veils. If he were to try to use a reasoned argument to validate rationality, he admits, he would be assuming the thing he is aiming to establish. This is how he approaches his target from the side, showing first how rationality perfects human understanding, then “reflecting on how reason has brought” material and moral progress. Unfortunately, while rationalists may feel assertive, non-believers are unlikely to convert.

Mr. Pinker, a professor at Harvard, has a lot to do. His previous book, “Enlightenment Now,” a hymn to the role of reason in history, received mixed reviews in 2018. It received high praise (including in The Economist), but also objections that he was simplistic, Panglossian and selective in his proofs. A personal attack followed last year, with a vicious and shoddy campaign demanding that the Linguistic Society of America reverse it. At the same time, in recent decades, research in economics and psychology has underlined the extent to which Homo sapiens falls short of rational beings who maximize their economic well-being and engage in a truth-distilling debate.

Since Mr. Pinker cannot simply argue for reason, seven of the book’s 11 chapters instead present a rationalist catechism – a primer of formal logic, probability, causation, etc. In these passages, he justifies reason by showing what it can do, using games and logical puzzles.

For example, imagine that 1% of women have breast cancer and a test for the disease is 90% accurate, but it reports false positives 9% of the time. If a woman tests positive, what is the likelihood that she will have the disease? The most common response among a sample of physicians was 80-90%, but the correct response is only 9%. The reason is that false positives in the 99% of women without breast cancer exceed true positives in the 1%. Without more data, you can’t say more about whether this particular woman is a true positive or a false one.

At first glance, the error of physicians is overwhelming evidence against human rationality. However, in an ingenious play of intellectual judo, Mr. Pinker turns the argument against the irrationalists. The fact that people are easily confused by probabilities, he writes, is no more proof that they are incapable of reasoning than optical illusions are proof that people cannot understand what. they see.

They are led astray in part by the way the questions are asked. By way of illustration, Mr. Pinker quotes “the Linda problem”, first posed by famous academics Daniel Kahneman and Amos Tversky.

Linda is 31 years old, single, straightforward and very bright. She specialized in philosophy. As a student, she was deeply concerned about issues of discrimination and social justice, and also participated in anti-nuclear protests. Please indicate the probability of each of these statements:
Linda is a primary school teacher.
Linda is active in the feminist movement.
Linda is a social worker in psychiatry.
Linda is a bank teller.
Linda is an insurance salesperson.
Linda is a bank teller and is active in the feminist movement.

Respondents tend to say that Linda is more likely to be a feminist bank teller than a simple bank teller, which cannot be true as the body of bank tellers includes all feminists and not. -feminists. Mr Pinker argues that such cognitive illusions can arise because people use their intelligence to make assumptions about a social reality in which they meet a person called Linda, rather than presenting the problem as a logical puzzle. When they are told to imagine 1,000 women like Linda and asked how many fall into each category, the error rate drops.

QAnon and on
Always optimistic, Mr. Pinker sees the glass half full. He rejects the idea that the human brain is “a basket of delusions”. The rationalistic techniques he describes help people correct prejudices and hasty judgments. They extend the remarkable thought powers of humans, just as microscopes and telescopes extend the range of their sight. The miracle is not that people make mistakes, but the ease with which we can help them overcome them. Anyone can learn to reason better; indeed, Mr Pinker goes on to say that rationality should join reading, writing and arithmetic as the fourth R.

This is all great, but it produces an inverted one-pound donut. To start and end, Mr. Pinker serves portions of jam, in which he discusses today’s attacks on sanity among anti-vax conspiracy theorists on the right and social justice warriors on the left. In between is this puzzle-solving ring designed to show that people are capable of being rational. For all their usefulness, these seven chapters are separate from the drama of the moment and surprisingly spockian in their lack of empathy. When Mr. Pinker finally states on page 283 that “This is the chapter most of you have been waiting for,” you wonder why a benevolent editor didn’t rush him to get to the point sooner.

The pity is that when Mr. Pinker writes about the conspiracy and outrage that has plagued American public life, he has a lot to say that is interesting. He’s wise enough not to blame everything on social media, or to claim that just elucidating Bayes ‘theorem would temper QAnon supporters’ feverish dreams about Democratic child murderers. Instead, he observes how humans evolved “not as intuitive scientists but as intuitive advocates,” using motivated reasoning to fight. People are titillated by conspiracy and gossip. And story and myth have a psychological and sociological function beyond literal truth and lies.

Rather than explore these ideas in more depth, however, Mr. Pinker rushes to argue that reason is the best defense against them. Rationality is impartial, he observes. In this, it corresponds to the ethical idea that a just system is a system that treats people without passion. Rationality, then, he writes with exultation, is not just a cognitive virtue, but a moral virtue. As for the critics who accuse him of a naive faith in progress, they misunderstand him. In fact, he believes rationality is what snatches progress from a ruthless universe. To illustrate his point, Mr. Pinker ends with a parade of thinkers such as Erasmus, John Locke and Jeremy Bentham who have paved the way for material and moral improvements by deploying reason against cruelty and violence.

Yet that will not be enough. Rationality implies that people know they are right. And since the French Revolution, being right has been used to justify appalling crimes. Mr. Pinker would undoubtedly characterize the Terror as a perversion of reason, just as Catholics call the Inquisition a negation of the love of God. It didn’t always seem like that back then.

Mr. Pinker is on the side of the best angels. He is right about the value of reason. He recognizes the contingency of what is known. But it places too little emphasis on the need to temper rationality with skepticism and how certainty slides into pride. He doesn’t care enough about how rationality merges with the rest of a person’s perspectives. Like many donuts, this book has a hole in the middle.