Across the country, police officers have very little incentive to tell the truth. Is that such a crazy thing to say?

No, it is not so crazy, says lawyer and Ohio State professor Michelle Alexander. In a convincing essay, she lays out how, even under oath, police officers in the United States face very little penalty for lying to a courtroom with a defendant's life in the balance. If their word is not enough to convict, if their testimony is so unbelievable that the case is dismissed, then " the officer is free to continue business as usual."

But is there more to this culture of lying than just the thrill of ruining someone's life?

Police departments have been rewarded in recent years for the sheer numbers of stops, searches and arrests. In the war on drugs, federal grant programs like the Edward Byrne Memorial Justice Assistance Grant Program have encouraged state and local law enforcement agencies to boost drug arrests in order to compete for millions of dollars in funding. Agencies receive cash rewards for arresting high numbers of people for drug offenses, no matter how minor the offenses or how weak the evidence.

Ah, right. The numbers game. That's illegal though, yeah?

For the record, the New York City police commissioner, Raymond W. Kelly, denies that his department has arrest quotas. Such denials are mandatory, given that quotas are illegal under state law. But as the Urban Justice Center's Police Reform Organizing Project has documented, numerous officers have contradicted Mr. Kelly. In 2010, a New York City police officer named Adil Polanco told a local ABC News reporter that "our primary job is not to help anybody, our primary job is not to assist anybody, our primary job is to get those numbers and come back with them."

So once we get rid of those quotas, unofficial or not, then police will stop lying? It's not like it's human nature, right?

Research shows that ordinary human beings lie a lot - multiple times a day - even when there's no clear benefit to lying. Generally, humans lie about relatively minor things like "I lost your phone number; that's why I didn't call" or "No, really, you don't look fat." But humans can also be persuaded to lie about far more important matters, especially if the lie will enhance or protect their reputation or standing in a group.

Well, fine! I guess we'll have to stop encouraging police officers to lie to make themselves look better, which means not elevating and privileging them to a point where they exist above the law.

And that sounds pretty crazy!