Julie Beck in The Atlantic:
Language is the hallmark of humanity—it allows us to form deep relationships and complex societies. But we also use it when we’re all alone; it shapes even our silent relationships with ourselves. In his book, The Voices Within, Charles Fernyhough gives a historical overview of “inner speech”—the more scientific term for “talking to yourself in your head.”
Fernyhough, a professor at Durham University in the U.K., says that inner speech develops alongside social speech. This idea was pioneered by Lev Vygotsky, a Russian psychologist who studied children in the 1920s and noted that when they learned to talk to other humans, they also learned how to talk to themselves, first out loud, and eventually, in their heads.
Inner speech, Fernyhough writes, isn’t bound by many of the conventions of verbal speech. For one, we can produce it much faster when we don’t have to go at the pace required to use tongues and lips and voice boxes. One researcher the book cites clocks inner speech at an average pace of 4,000 words per minute—10 times faster than verbal speech. And it’s often more condensed—we don’t have to use full sentences to talk to ourselves, because we know what we mean.
But it does maintain many of the characteristics of dialogue. We may imagine an exchange with someone else, or we may just talk to ourselves. But that doesn’t mean it’s not a conversation. Our minds contain many different perspectives, and they can argue or confer or talk over each other.