Despite centuries of guesswork and decades of serious study, just how children acquire their native language remains mysterious. Parents are amazed at how much language children learn and how fast they learn it. Yet the more science discovers about this process, the more mysterious it seems. The fact, for example, that a kindergarten child enrolls in school with an average vocabulary of 10,000 words means she has learned about 8 words per day since she began talking. Moreover, an infant can discriminate more sounds from languages she's never heard before than the same kindergartener. What accounts for this magic?