Publishers Weekly
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It’s not what everyone knows that counts but what everyone admits they know, according to this labyrinthine pop-sci treatise. Harvard cognitive psychologist Pinker (The Better Angels of Our Nature) recaps research—his own and others’—into common knowledge, the store of information that everyone knows and, crucially, is universally acknowledged to be true (as illustrated by the folktale “The Emperor’s New Clothes,” wherein everyone can see the ruler is naked, but it only becomes common knowledge when a naive child publicly declares it). Pinker analyzes how common knowledge enables the coordination of mutually beneficial outcomes: a public protest establishes the common knowledge of political dissatisfaction and allows protestors to take unified action, for example. Elsewhere, a chapter on cancel culture—Pinker has spoken out against its eruptions at Harvard—argues it’s an attempt by ideologues to band together to protect common knowledge from infiltration by politically incorrect ideas. Pinker’s discussions of these findings are intriguing if not earthshaking, but the scientific apparatus he assembles—replete with psych experiments into “recursive mentalizing,” or “thinking about thoughts about thoughts”—can feel overblown and onerous. The result, in a lapse from Pinker’s usual brilliance, is a taxing outing that yields mostly pedestrian insights. (Sept.)

Library Journal
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Common knowledge, or things we know that others also know, creates different incentives for how people solve individual coordination problems and understand significant societal issues. This is Pinker (psychology, Harvard Univ.; Enlightenment Now: The Case for Reason, Science, Humanism, and Progress) in short and accessible mode, exploring the psychology and philosophy of common knowledge for non-specialists. Much of Pinker's argument is accomplished by explaining aspects of game theory and how they apply to daily life. For example, how do two friends manage a rendezvous at a café when their phones are dead? Understanding these concepts in innocuous contexts leads to more complex questions around, for example, the risks of sexual propositions. The last part of the book turns less objective, as Pinker makes the case for academic freedom and explores questions of common knowledge and its role, or lack thereof, in scholarly research. VERDICT An accessible primer on game theory and the psychology of making decisions, for popular science readers.—Margaret Heller

Kirkus
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Pinker continues his explorations of the hidden social functions of language and thought with this look at common knowledge. Common knowledge, as cognitive science Pinker lays it out here, lends itself to the game theory beloved of economists and strategists: Do I know something that you don’t? Can we agree, in order to produce best outcomes, thatX meansX andY meansY? Pinker explains at the outset that “withprivate knowledge, person A knows something, and person B knows it. Withcommon knowledge, A knows something, and B knows it, but in addition, Aknows that B knows it, and B knows that A knows it”—a shared set of data, facts, and assumptions that enable not only cooperation but also coordination. That coordination, Pinker holds, is essential to the functioning of society: Our shared visions allow us to build economies, polities, communities, for which reason he adds that a better term for “common knowledge” would be “mutual knowledge,” which more easily accommodates agreeing on “nonphysical realities.” Pinker offers a vivid example when he notes that people don’t rise up against dictators easily because of the unspoken assumption that everyone else supports the regime, but things can get rolling when a public demonstration yields “the common knowledge needed to coordinate resistance.” Timely, that. Common knowledge has its negative aspects, he adds, as when people come to consensus about some point or another by way of shared media and then move together to punish transgressors. The swiftest way to be misunderstood, he notes, is to use irony or indirect speech, much as they help disguise our intentions. Pinker writes fluently, though there’s plenty of arcana from neuroscience, linguistics, and other fields floating around here. While it’s not necessary to have read Noam Chomsky, Antonio Damasio, Daniel Kahneman, and other cognitive scientists to follow Pinker’s arguments, it helps. A revelatory, if sometimes challenging, look at the traps and rewards that lie within our words. Copyright © Kirkus Reviews, used with permission.