The smallish words that tie our sentences together, sometimes called “filler words” or even “junk words,” consist of articles, pronouns, and prepositions, including the, this, I, though, and, there, that. After examining these words and how they are used, Dr. James Pennebaker of the University of Texas discovered the way people use filler words may predict how well they will get along with a stranger or even reveal whether they are telling a lie. "These are the words that we don't pay attention to, and they're the ones that are so interesting," Pennebaker told NPR.

Among his many experiments, Pennebaker recorded the conversations of speed daters in an attempt to predict the likelihood that two people would end up on a future date. He fed these individual speed conversations into a program he built with his students in the early 1990s, the Linguistic Inquiry and Word Count program, along with information about how the people themselves were perceiving the dates. What he discovered surprised even him.

By analyzing their language, he could predict who would go on a date at higher rates than the individuals themselves, he told NPR. In particular, when two people used pronouns, prepositions, and articles in similar ways and at similar rates, those two people were much more likely to end up on a date. This, despite the fact that function words are generally ignored by most of us; we simply don’t hear them because we are concentrating instead on content words — the verbs and specific nouns.

Oddly, the reason similar use of language predicted whether two people would become a couple is not a matter of similar people being attracted to each other. Some of the couples formed during the speed dating experiment were pairings of very unalike people. No, the similarity in language use occurred only after a couple met. According to Pennebaker, when you are around someone who interests you, your language automatically shifts and you begin to mimic the language style of that person. So the more a couples' use of language begins to match, the greater the likelihood they will continue to be dating in three months, he found.

Another study Pennebaker conducted focused on the speech of liars. “Compared to truth-tellers, liars showed lower cognitive complexity, used fewer self-references and other-references, and used more negative emotion words,” Pennebaker and his co-authors noted in the study. In fact, his computer-based text analysis correctly spotted the liars from the truth-tellers at a rate of 61 percent of the time.

Interestingly, Pennebaker and his colleagues suggest the reason liars avoid first-person pronouns, such as I and me, might be an attempt to distance and disassociate themselves from the lies they are telling. And, the guilt and conflict a liar feels when telling an untruth might cause anxiety and tension, leading to the use of negative emotion words. Ultimately, then, articles, pronouns, and prepositions “are, in many respects, as meaningful as specific nouns and verbs in telling us what people are thinking and feeling,” wrote the authors. Clearly lying is not always a matter of what a person says, but how they say it.