A fundamental goal of linguistic theory is to explain how natural languages are acquired. This paper describes some recent findings on how learners acquire syntactic knowledge for which there is little, if any, decisive evidence from the environment. The first section presents several general observations about language acquisition that linguistic theory has tried to explain and discusses the thesis that certain linguistic properties are innate because they appear universally and in the absence of corresponding experience. A third diagnostic for innateness, early emergence, is the focus of the second section of the paper, in which linguistic theory is tested against recent experimental evidence on children's acquisition of syntax.

In my Response to the target article, “Natural Language and Natural Selection,” co-authored by Steven Pinker and Paul Bloom (BBS 13(4):769), the journal printed the following sentence, “Rather, different mutations are stored independently in different lineages, and recombination brings them together to form vast numbers of new combinations, in people, in their descendents,” in error. The sentence should have read: “Rather, different mutations are stored independently in different lineages, and recombination brings them together to form vast numbers of new combinations, in parallel, in their descendents.”