This article notes the persistence of questions that occupied theorists of language in the eighteenth century: How does language evolve from gesture to arbitrary signs? Does language convey propositions or social attitudes? These and other questions are addressed in an account of the main areas of linguistic theory in the eighteenth century: the relationship between language and mind, the origin and progress of language, and language as a means of persuasion and an object of taste. Concluding with a discussion of some likely areas of future research into eighteenth-century linguistic theory (its “cognitivism,” its interest in the human-animal boundary, its interest in language diversity), the article suggests that language studies are crucial to consider when determining what is meant by “the Enlightenment.”