Crossing Boundaries focuses on the intellectual and social factors that led to the emergence and first flowering of the German essay. John McCarthy challenges traditional ways of thinking about literature by concentrating on the impact of Enlightenment philosophy, rhetoric, genre theory, and literary life on the evolution of essayistic writing in German.

Taking issue with the commonly held view that the German essay did not evolve until after 1750—and then only under the influence of French and British models—McCarthy argues that Enlightenment skepticism and the social ideas of the galant homme spawned an early native form. Varieties of that form, a kind of writing the author terms "essayism," were pervasive, extending into a variety of genres in the hands of writers such as Leibniz, Lessing, Goethe, Schiller, and Schlegel. He combines in-­depth analyses of representative essays with unique adaptations of recent developments in literary theory, intellectual history, literary history, and social history.

McCarthy's argument is centrally concerned with the critical reexamination of the categories of knowledge and of the means of disseminating information that characterized eighteenth-century thought. The essay, an experimental form that crosses boundaries of discipline and genre, is derived from this new emphasis and is the clearest reflection of the dialectic interplay among thinking, writing, and reading. It is also, as such, the genre or mode most closely related to Enlightenment philosophy itself.