Ever since philosophers speculated about a “cerebroscope,” a mythical device that would display a person’s thoughts on a screen, social scientists have been looking for tools to expose the workings of human nature. During my career as an experimental psychologist, different ones have gone in and out of fashion, and I’ve tried them all—rating scales, reaction times, pupil dilation, functional neuroimaging, even epilepsy patients with implanted electrodes who were happy to while away the hours in a language experiment while waiting to have a seizure.

Yet none of these methods provides an unobstructed view into the mind. The problem is a savage tradeoff. Human thoughts are complex propositions; unlike Woody Allen speed-reading War and Peace, we don’t just think “It was about some Russians.” But propositions in all their tangled multidimensional glory are difficult for a scientist to analyze. Sure, when people pour their hearts out, we apprehend the richness of their stream of consciousness, but monologues are not an ideal dataset for testing hypotheses. On the other hand, if we concentrate on measures that are easily quantifiable, like people’s reaction time to words, or their skin response to pictures, we can do the statistics, but we’ve pureed the complex texture of cognition into a single number. Even the most sophisticated neuroimaging methodologies can tell us how a thought is splayed out in 3-D space, but not what the thought consists of.

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As if the tradeoff between tractability and richness weren’t bad enough, scientists of human nature are vexed by the Law of Small Numbers—Amos Tversky and Daniel Kahneman’s name for the fallacy of thinking that the traits of a population will be reflected in any sample, no matter how small. Even the most numerate scientists have woefully defective intuitions about how many subjects one really needs in a study before one can abstract away from the random quirks and bumps and generalize to all Americans, to say nothing of Homo sapiens. It’s all the iffier when the sample is gathered by convenience, such as by offering beer money to the sophomores in our courses.

This book is about a whole new way of studying the mind. Big Data from internet searches and other online responses are not a cerebroscope, but Seth Stephens-Davidowitz shows that they offer an unprecedented peek into people’s psyches. At the privacy of their keyboards, people confess the strangest things, sometimes (as in dating sites or searches for professional advice) because they have real-life consequences, at other times precisely because they don’t have consequences: people can unburden themselves of some wish or fear without a real person reacting in dismay or worse. Either way, the people are not just pressing a button or turning a knob, but keying in any of trillions of sequences of characters to spell out their thoughts in all their explosive, combinatorial vastness. Better still, they lay down these digital traces in a form that is easy to aggregate and analyze. They come from all walks of life. They can take part in unobtrusive experiments which vary the stimuli and tabulate the responses in real time. And they happily supply these data in gargantuan numbers.

Everybody Lies is more than a proof of concept. Time and again my preconceptions about my country and my species were turned upside-down by Stephens-Davidowitz’s discoveries. Where did Donald Trump’s unexpected support come from? When Ann Landers asked her readers in 1976 whether they regretted having children and was shocked to find that a majority did, was she misled by an unrepresentative, self-selected sample? Is the internet to blame for that redundantly named crisis of the late 2010s, the “filter bubble”? What triggers hate crimes? Do people seek jokes to cheer themselves up? And though I like to think that nothing can shock me, I was shocked aplenty by what the internet reveals about human sexuality—including the discovery that every month a certain number of women search for “humping stuffed animals.” No experiment using reaction time or pupil dilation or functional neuroimaging could ever have turned up that fact.

Everybody will enjoy Everybody Lies. With unflagging curiosity and an endearing wit, Stephens-Davidowitz points to a new path for social science in the twenty-first century. With this endlessly fascinating window into human obsessions, who needs a cerebroscope?

—Steven Pinker, 2017