What distinguishes a fling that ends in tears from long-term love? Past research suggests that the most successful couples share common interests, values and personality traits. Now new research published in Psychological Science proposes that the simplest words lovebirds use to speak to each other also make a difference—both in determining how attracted they are and how likely they are to stay together.

James Pennebaker and his colleagues at the University of Texas at Austin recorded 40 men and 40 women as they participated in a speed-dating exercise in which they talked to 12 strangers of the opposite sex for four minutes apiece. Later, the subjects rated each date based on how much they seemed to have in common and whether they wanted to see the person again. Pennebaker analyzed the participants’ conversations based on their use of pronouns and articles, such as “him,” “the,” “and,” “as” and “be.” These function words are used in most contexts and are processed rapidly and unconsciously. [For more on how Pennebaker uses function words to reveal personality and other traits, see “You Are What You Say,” by Jan Dönges; Scientific American Mind, July/August 2009.]

The pairs who used similar types of function words with similar frequencies, he found, were more likely to want to see each other again, regardless of how much they felt they had in common. In a follow-up study, Pennebaker compared the language used by 86 couples in committed relationships via writing samples from instant messages. He found that the more their function words matched, the more likely they were to be together three months later, irrespective of how happy they said they were in their relationships at the time.

The big question is whether individuals feel more aligned to others who already talk the way they do or whether they adapt their language to match that of individuals they really like. Pennebaker admits that both are possible, but he believes the latter is the driving force: language, he says, predicts relationship success because it reflects how well couples listen to each other. What is Pennebaker’s advice for living happily ever after with a loved one, then? “Pay closer attention to the other person,” he says.