In this chapter we discuss a shift in Chomsky’s thinking about the extent to which the acquisition of language is based on a language-domain-specific innate system. The initial idea was that children develop their mental grammar based on two factors: a “richly articulated” innate system, called Universal Grammar (UG), and the language input. Chomsky later decided that the innate language faculty can be reduced to a single operation, “recursive Merge.” This made it necessary to acknowledge a third category of factors that plays a sizeable role in the emergence of mental grammars. These third factors cover a mixed bag, including “general learning systems” (those that empiricists would always have emphasized) and another kind of factor, which Chomsky finds more interesting: “natural laws of form” that are grounded in the laws of physics and perhaps ultimately in mathematical principles. We will discuss this notion of third factors, and I will show that attempts to explain the structure of human mental faculties in terms of principles that determine much, if not everything, in the natural world (both mind-internal and mind-external) are widespread and have a long tradition.

Chapter 1 introduces the central theme of the book, which is in essence the question of how human beings come to know what they know. Trying to answer this question, while considering different views, leads to getting involved in the infamous ‘nature–nurture debate’. I will discuss what kinds of more specific questions we ask when we engage in this debate and also how this debate has changed over time. We then focus our attention on how this debate applies to human language. Specifically, this chapter discusses the Innateness Hypothesis for language, i.e., Noam Chomsky’s idea that children are born with a specific “instinct” to acquire language. This chapter also contains a preview of all the subsequent chapters.