From talk to telepathy: The spontaneous use of insider language in casual conversation

Close friends seem to communicate almost telepathically. A single word or phrase can be loaded with meaning that would take pages of text to explain to an outsider. This linguistic compression is undeniably efficient. But is efficiency the only reason friends often speak in code? In a series of studies, we show that when people use “insider language” with each other they feel closer. Friends, as expected, use insider language more frequently than strangers, but even strangers are able to incorporate it into their conversations. While the content of insider language varies between friends and strangers, both groups experience heightened connection when it is used. These results suggest that the human ability to say more with less confers a social advantage beyond mere efficiency. These findings also highlight a potential limitation of large language models, which, trained on explicit text, may struggle to grasp how communication shifts with intimacy and may be unable to generate insider language to foster closeness.