At least since the time of Aristarchus in Alexandria, who died one hundred forty-five years before Christ, a body of knowledge or, if you prefer, a “science of literature” has been built up over the centuries. The Renaissance revived and codified it and the Romantic movement gave impetus to its enormous expansion and institutionalization in the later nineteenth century. Though deep changes in methods and emphases came about in the first half of this century, one can say that literary scholarship has flourished uninterrupted—at least in all Western countries—for roughly two centuries.

One can distinguish among three main branches of literary study. First, there is theory, which is concerned with the principles, categories, functions, and criteria of literature in general. Theory is the term now preferred to the older “poetics,” since “poetics” seems limited to...