It wasn’t so long ago that respectable psychologists didn’t really talk about “brainwashing.” The term had the slightly kitschy flavor of other Cold War embarrassments—C.I.A. spy cats and Reds-under-the-bed paranoia. But Google’s indispensable Ngram Viewer, which analyzes how frequently phrases appear in printed texts, confirms that the past two decades have seen an uptick in the word’s usage. What’s bringing brainwashing back?

One potential answer is the rise of technologies suspected of having mind-controlling powers, chief among them social media. Another is the entrenched political polarization of our time. When the cousin you kicked a soccer ball around with as a child starts spouting unhinged certainties about viruses, vaccines, and climate change—beliefs he treats as beyond debate—you might wonder: What happened to him? This isn’t just an ordinary disagreement. Could he have been . . . brainwashed?

Don’t get smug; he’s wondering the same thing about you. A few years ago, Psychology Today posted a checklist under the headline “Your Friend Might Be Politically Brainwashed If . . .” The last item on the list: “They assume that everyone who disagrees with them must be brainwashed.” So wait—does entertaining the possibility of having been brainwashed mean that you haven’t been? Or is that too easy?

Several recent books have taken up the subject of brainwashing—among them Daniel Pick’s “Brainwashed: A New History of Thought Control” (Profile), Joel E. Dimsdale’s “Dark Persuasion: A History of Brainwashing from Pavlov to Social Media” (Yale), and Andreas Killen’s “Nervous Systems: Brain Science in the Early Cold War” (HarperCollins). They share a scholarly squeamishness about the word they are forced to use for their subject matter. “Yes, the term brainwashing is silly and unscientific,” Dimsdale writes. “No one ever meant it literally, but the metaphor is a powerful one.”

In the new book “The Instability of Truth: Brainwashing, Mind Control, and Hyper-Persuasion” (Norton), Rebecca Lemov, a historian of science at Harvard, takes a different approach. She is often asked, she says, whether brainwashing really exists. “The answer is yes,” she writes, without any it-depends-what-you-mean-by hedging. In fact, she continues, “what we call brainwashing is not rare but common.”

Of course, words like “brainwashing” have no fixed meaning independent of their usage, which can be imprecise and expansive. When Frantz Fanon wrote of colonial efforts at lavage de cerveau in Algeria, or when a commentator in the seventies accused President Richard Nixon of having “brainwashed” white workers into fearing Communist infiltration, the word was gesturing at something, however loosely defined.

Yet the term’s recent resurgence raises suspicions. Accusations of brainwashing aren’t neutral claims; they offer a particular explanation for why someone holds beliefs we find preposterous. That explanation attributes those beliefs to deliberate manipulation instead of rational argument or personal conviction. In doing so, it may recast those with “deplorable” beliefs as victims rather than agents, deserving of not just condemnation but sympathy—and, perhaps, treatment. In the seventies heyday of the cults, that treatment was called “deprogramming.” Is this what our addled cousins need? A systematic re-indoctrination into conventionality?

The earliest appearances of the concept “brainwashing,” Lemov writes, occurred in the mid-twentieth century, in the files of the Office of Strategic Services, a precursor of the C.I.A. The term came to prominence owing in large part to the writings of an American journalist named Edward Hunter. He claimed that it was a rendering of a Chinese phrase, but it may have been, as he elsewhere claimed, a coinage of his own to describe Chinese persuasion techniques.

These techniques were most famously applied during the Korean War. As a prisoner of war, Morris R. Wills faced a gamut of privations—he was left malnourished and consigned to filthy conditions amid the ever-present threat of execution. Horror alternated with boredom. Conditions improved when Wills was transferred to what was called Camp One. The food got better, letters could be sent home, and there were even volleyball games.

That was, it seems, an early stage of a procedure known as reëducation. Wills was identified as a member of the exploited classes, a promising target for the method. Reflecting on his experiences many years later, he said, “Brainwashing is not done with electrodes stuck to your head.” It was, rather, “a long, horrible process by which a man slowly—step by step, idea by idea—becomes totally convinced, as I was, that the Chinese Communists have unlocked the secret to man’s happiness and that the United States is run by rich bankers, McCarthy types, and ‘imperialist aggressors.’ ”

The theory behind this method, as articulated by Chairman Mao, didn’t sound so bad. People could not be forced to become Marxists, Mao wrote. He recommended, instead, “democratic” methods of “discussion, criticism, persuasion, and education.” An important stage of the process was called “speaking bitterness.” American G.I.s, like the Chinese peasants on whom the method had first been tried, had a great deal of bitterness to speak: of racism and poverty back home, and of discrimination within the armed forces. Wills was made to introspect, to write an autobiography. He and other P.O.W.s were subjected to hours of lectures on Marxist theory.

Faced with the demand to justify “the American system,” Wills—unable to articulate what that even was—found himself moving in what his captors called a Progressive (as opposed to Reactionary) direction. American society was rotting, he came to believe; the Chinese way was the future. He chose not to be repatriated. But, where other prisoners who made the same decision were sent to work on farms and in paper mills, he was sent to the People’s University in Beijing.

The brainwashing process was never complete. Ostentatious acts of “repentance” were repeatedly demanded—Wills had already had to participate in “self-criticism” seminars. He was now taught more about Marxism and the history of China. He even witnessed a public execution. But he ended up staying in China for twelve years.

Wills’s retrospective accounts of his experience, once he was back in the United States and in a position to reflect on what had been done to him, are illuminating. It is plain that his Chinese captors had succeeded, at least for a time, in producing a genuine change of mind. He was, as he himself put it, “totally convinced.”

If we take Wills at his word, we might wonder about Mao’s claim that nobody can be coerced into sincere belief. In professing this, Mao echoes an old idea within modern European thought, one given its most influential expression in John Locke’s 1689 tract, “A Letter Concerning Toleration.” Locke condemned the use of coercion in matters of faith—the sort of thing we now associate with the Spanish Inquisitors—and among his arguments was that it simply couldn’t work. Real belief is a product of the “inward persuasion of the mind,” he wrote. An effective torturer can make his victims move their limbs as he tells them to, or even say the words—professions of faith, confessions of guilt—that he whispers into their ears. But “such is the nature of the understanding, that it cannot be compelled to the belief of anything by outward force.”

Locke’s point is connected to a more general philosophical claim about belief: that no one can just decide to believe something. Try believing, for instance, that the magazine (or computer or tablet or phone) in front of you is a venomous snake, or that your coffee mug is made of molten lava. You can cry out, if you like, but your steady heart rate will give you away.

For all that, you can surely be forced into situations where the desired conviction comes unbidden. Even in the seventeenth century, people saw the limitations of Locke’s view. An Oxford churchman named Jonas Proast agreed that belief could not be coerced directly, but, in his chilling words, the magistrate might lay “such Penalties upon those who refuse to embrace their Doctrine . . . as may make them bethink themselves.”

To force someone to believe something requires the concealment of the role that force has played in the process. The brainwashed can’t conceive of themselves as brainwashed; to do so would indicate that the brain remains unwashed. They can only coherently describe their experience as one of seeing the light, having their consciousness raised, being red-pilled. As Lemov quotes someone telling her about brainwashing: if the method works, it “erases itself.”

So, if your environment was tailored to exclude alternative views, should we say that you were being forced to believe something? Whether we call this coerced belief is a matter of terminological preference. Ways of making people believe things don’t divide neatly into the persuasive and the coercive—the brainwashing model gives the lie to that distinction. As Lemov writes, echoing the psychologist Edgar Schein, it is “neither pure persuasion nor sheer coercion but both: coercive persuasion.”

The phrase “coercive persuasion” effectively conveys the core objection to what it describes. It suppresses the fundamental exercise of human autonomy—it prevents you from making up your own mind. If that’s the case, would the criminal courts find you responsible for what you do when you’ve been brainwashed?

This question was decisively answered during the trial of Patricia (Patty) Hearst, in 1976. Two years earlier, Hearst, a granddaughter of the press magnate William Randolph Hearst, was an undergraduate at Berkeley. Her life changed forever when she caught the eyes of members of the Symbionese Liberation Army, an anti-capitalist guerrilla group. They abducted her and held her in a closet, blindfolded, for nearly two months. She was raped multiple times by the group’s leaders while in captivity, having been told that it would be “uncomradely” to refuse consent.

Shortly afterward, she was offered a nominal choice. Would she join them? Or did she wish to be freed? It was clear to her that the appearance of choice was illusory, that she was choosing between joining the group and being killed. She chose life. Or, as she later put it, “I accommodated my thoughts to coincide with theirs.” As with the Korean War P.O.W.s before her, mere pretense was not, under the circumstances, a real option. “By the time they had finished with me,” she later reflected, “I was, in fact, a soldier in the Symbionese Liberation Army.”

A little more than two months after her abduction, surveillance cameras captured Hearst robbing a bank in San Francisco, gun in hand. When she was eventually arrested, she weighed eighty-seven pounds and was—in the assessment of the psychologist Margaret Singer—“a low-I.Q., low-affect zombie.” The Yale psychiatrist Robert Jay Lifton interviewed Hearst for about fifteen hours and then declared her a “classic case” of brainwashing. During her time in custody, she repudiated her allegiance to the S.L.A. When she stood trial for her role in the bank robbery, her attorneys argued that she was a victim of coercion and duress.