When Pinocchio did it, everyone knew. But catching a real liar in in the act is not as easy.
Even before the war on terrorism, scientists were trying to find a way to identify liars by checking their vital signs or voice. Now, they are even more motivated.
What began with the polygraph machine almost a century ago has led more recently to approaches like one announced this month that uses thermal imaging to detect a blush around the eyes when someone is being deceptive. That method is being touted as an airport-friendly way to catch terrorists. Brain-mapping research, another technique, could eventually prove to be another almost foolproof way to detect dishonesty.
That kind of precision is enough to make even those who tell white lies a little nervous. It also raises questions about what role skirting the truth plays in situations where personal safety isn't at risk - and what the outcome would be if it weren't an option anymore.
Researchers say there's no need to worry about that just yet. "If you think about the methods that are going to be extremely accurate - like brain mapping - those are things the average person isn't going to have access to," says Michael Aamodt, a professor of psychology at Radford University, in Virginia.
For the average person, detecting lies has long been more art than high-tech science. People watch facial expressions and analyze tone of voice to figure out whether their meatloaf is really appreciated or their significant other is faithful. In fact, those are techniques researchers have picked up on and developed further.
Even when people employ their own observations, though, there is room for error. Different cultures have different habits when speaking to people, for example. Take eye contact - what one person might see as shifty, another might consider polite.
Such wiggle room may be a good thing. That some lies go undetected is good for society, say some who study deception. If everyone were forced to tell the truth all the time, the world would be an unpleasant place. In fact, experts often use the word "cruel" to describe such a place.
Think about the family that is told their loved one didn't suffer in a fatal car accident, even if the victim did. "It benefits the family, it hurts nobody," says Professor Aamodt. People don't always want to know the truth, either. Avoiding intentionally hurting people's feelings or making them angry may limit aggressive behavior in society, some observers say.
"Handling information is an alternative means of influence - an alternative to force," says David Nyberg, author of the 1993 book "The Varnished Truth: Truth Telling and Deceiving in Ordinary Life." If forced to voice our true feelings and beliefs about other people, we would engage in a lot more fighting, he adds.
To Mr. Nyberg, a recently retired professor of education, medicine, and philosophy at the State University of New York at Buffalo, lying is a subset of deception. He defines deception as the intentional or purposeful misrepresentation of some aspect of reality as we take it to be. "Looked at that way, it's not possible to conceive of ongoing relationships without it," he says.
Using his definition, a professor might observe that one of his students is going to have a difficult time succeeding, based on students who display similar characteristics. But instead of telling the student that he's doomed, the teacher might tell him that he will have to work hard if he wants to succeed.
The result, says Nyberg, is that the teacher is misrepresenting what he knows to be true in order to help the student.
Even if it were possible to do away with lying completely, scientists have yet to find Pinocchio's nose - that surefire way to tell if someone is telling a lie. One of the problems is that many tests - polygraphs, voice-stress analyzers, and even the latest thermal imaging - look at the arousal of a subject's emotions, which may or may not indicate honesty. This is why Aamodt and others say the approaches that measure brain activity have the potential to be more accurate.
"Maybe in our lifetime we're going to see some things that are 99.5 percent accurate, if they involve brain activity. But we're never going to get something that is 100 percent accurate. There's always going to be some error," he says.
One way to lessen the tension that white lies create in communication is not to tell them, says Sissela Bok, a Harvard scholar and author of the 1978 book "Lying: Moral Choice in Public and Private Life." Though doubtful that lying can be eradicated, she suggests that people should "lean over backwards" in an effort to avoid it, even in small doses, as it can lead to telling bigger untruths.
"We have to learn to exercise our imagination," to find ways of speaking that don't hurt people's feelings and at the same time aren't dishonest, she says in an interview.
Her alternatives include humor and even working to find more specific truthful answers. "Why tell a flattering lie about someone's hat, rather than a flattering truth about their flowers?" she writes in her book. People should also be aware of the effects of these lies. "What the liar perceives as harmless or even beneficial may not be so in the eyes of the deceived," she writes.
As more technology is developed for detecting deceit, one outcome may be that people become better at beating the system. In Nyberg's opinion, people may become better deceivers. "If we were clever enough to make machines that detect deception," he says, "the long-term consequence of that is that we would get cleverer at deceiving the machine."