Unlike the carefully scripted dialogue found in most books and movies, the language of everyday interaction tends to be messy and incomplete, full of false starts, interruptions, and people talking over each other. From casual conversations between friends to bickering between siblings to formal discussions in a boardroom, authentic conversation is chaotic. It seems miraculous that anyone can learn a language at all, given the haphazard nature of the linguistic experience. For this reason, many language scientists -- including Noam Chomsky, a founder of modern linguistics -- believe that language learners require a kind of glue to rein in the unruly nature of everyday language. And that glue is grammar: a system of rules for generating grammatical sentences.