As young children, how do we build our vocabulary? Even by age 1, many infants seem to think that if they hear a new word, it means something different from the words they already know. But why they think so has remained subject to inquiry among scholars for the last 40 years. A new study carried out at the MIT Language Acquisition Lab offers a novel insight into the matter: Sentences contain subtle hints in their grammar that tell young children about the meaning of new words.

The finding, based on experiments with 2-year-olds, suggests that even very young kids are capable of absorbing grammatical cues from language and leveraging that information to acquire new words. The study is published in the journal Psychological Science . "Even at a surprisingly young age, kids have sophisticated knowledge of the grammar of sentences and can use that to learn the meanings of new words," says Athulya Aravind, an associate professor of linguistics at MIT.

The new insight stands in contrast to a prior explanation for how children build vocabulary: that they rely on the concept of "mutual exclusivity," meaning they treat each new word as corresponding to a new object or category. Instead, the new research shows how extensively children respond directly to grammatical information when interpreting words. "For us it's very exciting because it's a very simple idea that explains so much about how children understand language," says Gabor Brody, a postdoc at Brown University, who is the firs.