The study focused on words called “function words.” These aren’t nouns and verbs; they’re the words that show how those words relate. They’re hard to explicitly define, but we use them all the time—words like the, a, be, anything, that, will, him, and and. How we use these words constitutes our writing and speaking style, says study coauthor James Pennebaker of the University of Texas at Austin.

“Function words are highly social and they require social skills to use,” he says. “For example, if I’m talking about the article that’s coming out, and in a few minutes I make some reference to ‘the article,’ you and I both know what the article means.” But someone who wasn’t part of that conversation wouldn’t understand.