All this leaves an important question: Can public pressures affect private preferences as well as public preferences? Kuran thinks so, and he offers a subtle and intriguing explanation, focusing not on the concealment of private preferences but on their transformation. Let's start with individuals. Suppose that you tend to believe that women, like men, should be educated, and that everyone should have the chance to become literate regardless of gender. Suppose, too, that this belief is inconsistent with existing social pressures (as it is in many parts of the world). Eventually you may change your private belief, making it conform with those pressures. This is because it can be extremely frustrating, even distressing, to believe something that other people think implausible, offensive or stupid. In order to reduce cognitive dissonance, dissenters may bring their private preferences into line with perceived public opinion. And in this way people who are oppressed by the status quo can come to collaborate in their own oppression. Thus, in discussing the caste system in India, Kuran adduces evidence that "Hindu ideology has contributed to the untouchables' acceptance of their deprivations as fair, that it has made many treat their wretched existence as natural, and that it has facilitated their complicity in an order that degrades them."

But Kuran is interested not only in what happens with individual agents. He wants to explain also how certain private beliefs get lost or abandoned as the content of public information changes over time. If certain thoughts are "unthinkable"--in the sense that people who entertain them are seen as uncivil or immoral--they may eventually become "unthought," that is, they disappear altogether. And so social pressures can make certain ideas disappear from public discussion. As this happens, people become less conscious of the disadvantages of what is publicly favored and more conscious of the advantages. In the long run, private opinion itself moves against the thought that is publicly disfavored. If you have never heard that women should be educated equally with men, or that caste systems offend equality of opportunity, or that likes and dislikes are a function of social pressures, you may well not think of these things at all. Thus Kuran offers an account of how ideas can change across generations. In the end, the effects of public opinion on private preferences come from a collective process, in which millions of people affect one another's views through interdependent acts of knowledge and "preference falsification."

Kuran applies these basic ideas to three case studies: the fate of communism; the caste system in India; and the spread of affirmative action in the United States (which, in his view, was "unwanted"). The discussion of communism is a highlight of the book. Offering many vivid anecdotes, he shows that communism persisted not only, or not mostly, because of brute terror, but also because of a "pervasive culture of mendacity." People joined organizations they abhorred, followed orders they considered nonsensical, cheered speakers they despised and ostracized dissidents they greatly admired. How could this have been? Kuran shows that all this could not have been the consequence of terror--state resources were often far too limited for that--and that it was largely a product of widespread perceptions of what other people thought, or thought normal. Thus, for example, a unanimous vote of the Writers' Union denounced Boris Pasternak as an enemy of the Soviet Union for producing Doctor Zhivago, even though they widely admired the writer and his novel. There were countless similar examples. In the Soviet Union, of course, force was relevant; but preference falsification also played a role.

In some cases, preference falsification produces a situation of stability, but in other cases it is possible to get rapid, unforeseen, even unforeseeable shifts. Recall that public preferences are a function of what people think that other people think. It follows that when in Eastern Europe the level of apparent public opposition started to rise, people's public preferences changed quickly, as they came closer to their private preferences. Not only governments, but also policies, customs and fashions "can be abruptly abandoned when people who have helped sustain [them] suddenly discover a common desire for change." In fact, societies reach a tipping point when social pressures no longer support the status quo, but even undermine it. Eventually it is support for the status quo that produces reputational loss. (Think of recent civil rights movements for blacks and women.) Thus "a revolutionary bandwagon may help create the discontent that keeps it in motion. Switches from the government to the opposition may alert essentially content people to the government's failings; or they may make people who had been resigned to the status quo recognize the possibility of political change."