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Three Ways To Know If Someone Is Probably Telling The Truth

James Pennebaker
James Pennebaker hopes in five years he'll have amassed the research needed to make a words-based lie detection system.

Social psychologist James Pennebaker wanted to know which small words can out a liar. He began by inspecting recommendation letters he wrote. Some were for students he was genuinely fond of; others, simply favors. He told Think host Krys Boyd the results of that study and others are consistent with three common features of untrue speech or writing found in research for The Secret Life Of Pronouns. 

If someone is being honest, Pennebaker says:

1. They tend to be less positive.

In those recommendation letters, "the people who I liked the most I didn’t use a lot of positive emotion words about," he says.

That's because there were concrete stories Pennebaker could tell about the merits of his former students - memorable acts that showed rather than told why he'd endorse them. Which leads us to:

2. They're able to be specific. 

"The ability to say what you didn’t do" in the course of a day, for example - not just what tasks you completed - can suggest honesty. 

This one, though, is tricky; there's no shortage of people who tell elaborate stories with a straight face. The business of spotting truth from lies is tough, psychologically, because of biases unknown to even us. 

"It’s fascinating how difficult it is," Pennebaker says. He notes that polygraphs are banned in court, but are likely more reliable than eyewitnesses. 

3. They'll use "I" a lot. 

This one is particularly interesting, because of the first-person-singular pronoun's traditionally accepted tie with narcissistic traits - and the way politicians are derided for using it, accordingly. Pennebaker points out President Obama employs the "I" less than any other president since Harry Truman, proving wrong some accusations of overuse.

Listen to the full conversation with Think host Krys Boyd. Think airs at noon and  pm on KERA 90.1 or you can stream the show live.