Before Steven Pinker wrote bestsellers on language and human nature, he wrote several technical monographs on language acquisition that have become classics in cognitive science. Learnability and Cognition, first published in 1989, brought together two big topics: how do children learn their mother tongue, and how does the mind represent basic categories of meaning such as space, time, causality, agency, and goals? The stage for this synthesis was set by the fact that when children learn a language, they come to make surprisingly subtle distinctions: pour water into the glass...