The study of the principles of literature does not belong to literary criticism, but to Æsthetics; or, to use Vico's distinction, not to Philology but to Philosophy. Textual criticism, and interpretative comment, are preliminaries of literary criticism, which begins only with the contemplation or æsthetic enjoyment of literature: that is, with that operation of reading which is made possible through the establishment of a correct text, and by the help, when needed, of a convenient commentary. In literary criticism proper Croce distinguishes three successive phases, or moments, answering respectively to the questions: What have I read? What is the value of that which I have read? Which is the genesis and fortune of this particular work? The first is the exposition or description--which in itself is a work of art of which another work of art is the subject; the second, the valuation or æsthetic judgment; the third, the history of the work under consideration. Outside these three moments or phases, Croce does not admit of any other independent critical operation: the research of the sources of a work is only part of the history of that work; comparative criticism is an instrument of historical criticism; philology in the strict sense of the word can in turn be used as a help to each of the three main operations, but when it is exclusively concerned with the general history of a language, it is no longer a literary discipline; bibliography is a mere external element of the history of the work; the study of the content is a literary study only if it is pursued in relation with either the exposition, valuation or history of the work, that is, when the work itself is viewed as literature, and not as a document for the purposes of another science or discipline; the biography of the author is an element of the genesis of the work, and therefore of its history, but its main interest is moral and not literary.