Rationality: What it is, why it seems scarce, why it matters

Periodically, by a rough estimate twice per decade, a new popular book aspires to shake our common understanding of rationality. Since this concept is not only the backbone of normative analysis in the behavioral sciences but also of the way people more generally understand normativity, the stakes are particularly high. Among past successful attempts to rethink rationality are, so to refresh the memory, books of the caliber of Gigerenzer (2007), Kahneman (2011), and more recently Mercier and Sperber (2017). Because of its straightforward title, Rationality, and one enticing part of its subtitle, the promise to tell us What it is, Steven Pinker’s latest work aspires to be one of those ground-breaking books. There are two reasons, however, why readers might resist the temptation to consider Pinker’s book a foundational one. One reason is that in most of its parts it reads like a pamphlet, in which a world-renowned public intellectual attempts to shake the conscience of a world too dramatically lacking in reason and rationality (Pinker dispenses evidence of this masterfully). The public intellectual posture was to be expected, since Pinker has recently been in the vortex of inflamed debates over sensitive societal topics, and this book is in many regards a learned continuation of those debates. Pinker presents himself as a staunch advocate of freedom of speech and critical thinking, seen as requirements for democratic societies whose degree of rationality he deems to depend on a society’s capacity to deal with its ‘taboos’. Because of this posture, the book may risk being underestimated by those looking for a pristine foundational discussion. But another reason not to regard this book as foundational is the fact that Pinker does not present in it a novel idea of rationality. The readership of economists is certainly the most well equipped to understand that. The book’s central part, seven-elevenths of the total, is a superbly accessible guide to the edifice of rationality from the ground floor of logic (chapter 3) up to probability (chapter 4), Bayesian reasoning (chapter 5), rational choice theory (chapter 6), statistical decision theory (chapter 7), game theory (chapter 8), and the distinction between correlation and causation (chapter 9). The other four-elevenths are a demonstration that humans do not master these subjects – let alone apply them correctly to life – and a plea for why we should. This shows that Pinker does not really venture into a quest for the essence of rationality; what rationality is seems uncontroversial from the start: ‘My own position on rationality’, he says more as an adept than as a pioneer, ‘is “I’m for it”’ (p. 36). His true goal is to convince people to embrace rationality, challenge their belief that it is something ‘uncool’ and ‘cerebral’ that would turn one into a ‘nerd’, a ‘wonk’, a ‘geek’, or a ‘brainiac’ (p. 35, italics in original), not to challenge the classical idea of rationality. But even if one might think that the polemicist’s tone and the support of a classical idea of rationality would hinder the book from being epoch-making, it would be a real mistake not to identify a genuine foundational intent in it. To uncover and assess such an intent is devoted the rest of this review. The starting point to understand the novelty of Pinker’s intent is to acknowledge that he is a cognitive psychologist: a cognitive psychologist who accepts the rationality toolbox of logic, probability, and rational choice theory as a normative benchmark. This may immediately remind economists of two other cognitive psychologists, Daniel Kahneman and Amos Tversky, who believe that humans should measure their rationality against what Pinker is not afraid to call ‘godlike reason’ (p. 320). But unlike Kahneman and Tversky, Pinker is far more optimistic on the descriptive side. He does