At least since Aristotle, and up to the end of the seventeenth century, the form of literary works, envisaged and appreciated for itself, independent of content, has never ceased to be one of the major concerns of critics and lovers of belles lettres. Theories of style, poetics, phraseology and grammar form an imposing and coherent collection; each generation has enriched it; opinions have changed but not methods or intentions: the formulation of rules of the art of writing is itself a genre with its own laws. All of this was true up to the day when there appeared, at first rather modestly, a new spirit manifesting itself in the nineteenth century by two tendencies, apparently contradictory but deriving from the same source, and each vigorously developing. On the one hand, the notion of style is widened, and the word expressing it, which up to that time only affected the domain of letters, is extended bit by bit to the fine arts, to all arts, to all kinds of activities. Diderot was the first to apply it to painting; today we speak casually about the style of a swimmer or of a tennis player. On the other hand, and concurrently, literary art found itself affected by a sense of inferiority.