From the Columbia Encyclopedia:
"aesthetics (ĕsthĕt'ĭks), the branch of philosophy that is concerned with the nature of art and the criteria of artistic judgment. The classical conception of art as the imitation of nature was formulated by Plato and developed by Aristotle in his Poetics, while modern thinkers such as Immanuel Kant, F. W. Schelling, Benedetto Croce, and Ernst Cassirer have emphasized the creative and symbolic aspects of art. The major problem in aesthetics concerns the nature of the beautiful.
Generally speaking there are two basic approaches to the problem of beauty-the objective, which asserts that beauty inheres in the object and that judgments concerning it may have objective validity, and the subjective, which tends to identify the beautiful with that which pleases the observer. Outstanding defenders of the objective position were Plato, Aristotle, and G. E. Lessing, and of the subjective position, Edmund Burke and David Hume. In his Critique of Judgment, Kant mediated between the two tendencies by showing that aesthetic judgment has universal validity despite its subjective nature. Among the modern philosophers interested in aesthetics, the most important are Croce, R. G. Collingwood, Cassirer, and John Dewey."