“Don’t treat me like an idiot,” a young man in a black parka said to a police officer in Zuccotti Park, on the evening of the day after the police had cleared it. The officer, identified by the yellow letters on his jacket as a member of the N.Y.P.D.’s community-affairs team, was telling people that it wasn’t safe to sit on the ledge of a granite planter, but the young man didn’t want to get down. “I can’t believe you’re saying this to me in the United States of America,” the young man continued. The risk seemed minimal, and he believed he had the right to take it. As people became aware of the exchange, video cameras, smart phones, and S.L.R.s swiveled.

The police officer, after a brief attempt at a stern manner, relented. The young man did not get down from his seat, although most of those next to him did. His tenacity made an impression on me, because I find it hard to imagine myself plumply saying “No” to a police officer’s request, even if the request seems less than fully justified. The incident reminded me that the police have no authority except insofar as they are enforcing the law. Courts have long trusted them with discretion in how they enforce the law, but “discretion” is a socially defined quality and ought to be the sort of thing that people challenge and discuss.

Is it possible to imagine a world without police? Actually it’s easy, if you’re a historian. London didn’t get a professional police force until 1829; New York didn’t get one until 1845. Before that, law enforcement was more of a private affair. Crimes at night were somewhat deterred by watchmen, who were in some cases volunteers and in others paid, but by day there was little to no government-organized, government-subsidized surveillance. If you were the victim of a crime, you generally had to identify the criminal yourself and then pay a fee to a government official such as a constable or a bailiff in order to have them bring the criminal to justice.

The system worked, however imperfectly. Most people don’t obey the law because they fear punishment; they obey it because they feel that they belong to society and share the values embodied in its laws. When a professional police force was first deployed in England, homicide rates had already been dropping for centuries. In “American Homicide,” the scholar Randolph Roth doubts that the introduction of police into America improved the prevention of violent crime. While murder did decrease in late-nineteenth-century America, Roth credits the taming effect of working in factories and even speculates that police may themselves have contributed to homicide rates, thanks to their unfortunate tendency to kill suspects in the course of their law-enforcement duties.

So why invent police? What are they for? In “The Institutional Revolution,” the economic historian Douglas W. Allen theorizes that their purpose was to preserve manufactured goods from theft. Before the nineteenth century, Allen writes, theft was easy to detect. If your transport was a horse, you could recognize it. (For that matter, it could recognize you.) Not only was your coat hand sewn, but a tailor looking at its fabric could probably tell who had woven it. If any of these items were stolen, they were easy to reclaim if they could be found. With the advent of the industrial revolution, handmade goods gave way to standardized commodities, which all look alike, and it ceased to be possible to know an object’s provenance just by looking at it. The phrase “possession is nine-tenths of the law” came into vogue, and it was made illegal to hold stolen goods. After all, once goods became untraceable, they were all too easy to fence.

Allen sees these changes as driven by economics. “When goods became more standardized,” he writes, “then it was efficient for theft to be resolved by police.” If his guess is correct, then the protesters at Occupy Wall Street are right to suspect that police and property are in cahoots. They have been ever since the police were invented.

Now that we have police, of course, it may no longer be possible to do without them. We still live in a world of commodities. But the implicit social contract between citizens and the police needn’t be immutable. It may have been economically efficient for the past century and a half to assign police officers custody of social authority in ambiguous situations, but the vectors of economic efficiency can switch direction.

The larger point of Allen’s book is that these vectors switched dramatically in the late eighteenth and early nineteenth century, permanently altering a number of social institutions—ranging from duelling to naval strategy to lighthouse maintenance. Thanks to steam power, chronometers, and standardized weights and measures, it became possible to know more about what other people were doing and to expect more of them. Allen calls it a “measurement revolution.” Previously the world had run on trust, bribery, and subtle forms of blackmail. Henceforth there would be performance reviews. One of the mysteries of economics, Allen writes, is that the economic boons of the industrial revolution lagged behind its arrival by about a generation or so. He believes that it took social institutions that long to adjust themselves to the new capacity for measurement.

Networked computers arrived some time ago, but their promised productivity advantages have also been slower in coming than expected. Maybe it’s because, in order to profit from them, our social institutions have to change once more. Change has been visible in, say, bookselling, but now maybe it’s also becoming visible in political institutions. Why does someone like me defer to a policeman, after all? It’s probably because, in the old days, if he and I were to present to a court conflicting narratives of what happened between us, the court would more or less be obliged to take his side, not because the court was certain he was right, but because the court had an institutional relationship with the policeman to maintain. Knowing that, it made sense for me to concede that the policeman had an advantage: he was going to have the privilege of telling our story.

But things are different nowadays. Smart phones have cameras, and almost everyone has a smart phone. A court is therefore less likely to be ignorant of what actually occurred between the policeman and me. The policeman and I may have videotaped it. Bystanders might have, too. I am reminded of the utopia dreamed of by the eighteenth-century anarchist William Godwin, who hoped that someday everyone in the world would become so sincere and so expressive that all sides of every story would be fully narrated, and there would no longer be any need to deceive. Everyone would be his own narrator, and in the world that this sincerity revealed, perfect knowledge would include perfect forgiveness.

Well, maybe, maybe not, but the resemblance of Godwin’s dream to our world of ubiquitous self-documentation by smart phone and self-narration via social media is hard to deny. (Godwin’s scheme may bring to mind Bentham’s panopticon, but Bentham was proposing wardens in supervision over prisoners; narration was to be concentrated. Godwin imagined citizens revealing the truth about themselves, and incidentally about one another; narration was to be distributed.)