To explain this remarkable collection of facts about language development, linguists have attempted to formulate a theory of linguistic principles that apply to all natural languages (as opposed to artificial languages, such as programming languages). These principles, known as linguistic universals, offer insight into the acquisition scenario set out before us: why language is universal, why it is mastered so rapidly, why there are often only loose or incomplete connections between linguistic knowledge and experience. These features of development follow from a single premise--that linguistic universals are part of a human 'instinct' to learn language, i.e., part of a biological blueprint for language development.