Aesthetics (Gr.Aesthetics 100103 perceptive, from Aesthetics 100104 I feel, or perceive by the senses), the science of the beautiful, first recognized as an independent branch of philosophy about the middle of the last century. Even the ancient philosophers had speculated upon the beautiful. Pythagoras tried to express its form in numerical proportions; Socrates and Plato united it with the good, and called the highest ideal by the compound name "kalokagathon "; Aristotle strove to give its laws in formulas; and later metaphysicians, down to the recent schools, continued these attempts to define its conditions and effect. But Baumgarten, a disciple of the German philosopher Wolf, and in 1740 professor of philosophy at Frankfort-on-tbe-Oder, first established its claims to the dignity of a separate science. He held that besides the divisions adopted by Wolf's system, namely, the capacity of knowing (intellect), the ultimate ideal and aim of which is the true, and the capacity of acting (will), the ultimate aim of which is the good, there exists also in the human mind a capacity of feeling, or perceiving by the senses (sensibility), the ultimate ideal and aim of which is the beautiful.

As logic determines the laws of intellect, and ethics those of will or action, so there should be a branch of philosophy, which he called aesthetics, to determine the laws of sensibility. He made the mistake of considering this faculty, by which men perceive the beautiful, a lower capacity founded in the mere exercise of sense (cognitio sensitiva); but Kant, who in his Kritik der Urtheilskraft accepted the general division given above, corrected this, and showed that the aesthetic perception, for which the senses form only a means, really falls within the province of the high power of judgment. After 1742 Baumgarten lectured regularly on aesthetics, and its place as a philosophical science was almost universally recognized. In this purely abstract psychological consideration of the subject he followed Kant, who held that the beautiful was the harmony between the understanding and the imagination; and, after him several other German philosophers of much less note. Hegel's great work (Aesthetik) also treats the subject from this point of view; and Fichte belonged entirely to the ideal school of writers on the aesthetic perception.

But the name aesthetics soon began to be received in a more practical acceptation, and to be especially applied to that part of the science of the beautiful which relates to the expression and embodiment of beauty by art. Schiller first turned speculation in this direction; and Schelling, though devoting much study to the abstract, still contributed largely to the useful endeavor to bring the beautiful to the actual knowledge of men, rather than to analyze its psychological effects; and from their time this approach to the identification of the ideal and real has formed the chief and ultimate aim of the study of aesthetics. Two widely different theories as to the realization of the beautiful in art have been adopted by the different schools. One, the method a priori, strives by abstract reasoning to determine the laws of the beautiful, with which artists must comply; the other, the method a posteriori, seeks for the beautiful in existing works of art, and from the results of such investigation makes practical rules for future guidance.

The former has among its adherents most of the German, and the latter nearly all the English and French writers on aesthetics. - Those German authors whose works best deserve study are as follows: A. G. Baumgarten, Aesthetica (Frankfort-on-the-Oder, 1750); Georg Friedrich Meier, Anfangsgrunde aller schonen Wissen-schaften (1748); Hegel, Aesthetik (Berlin, ed. 1842-3); Weisse, System der Aesthetik (Leip-sic, 1830); Schiller, Aesthetisclie Briefe, in Cotta's editions of his works; Zimmermann, Geschichte der Aesthetik (Vienna, 1858); Vi- seher, Aesthetik, oder Wissenschaft des Schonen (Reutlingen, 1846-'57); Zeising, Aesthetische Forschungen (Frankfort, 1855); Kostlin, Aesthetik (Tubingen, 1863); Gottfried Semper, Der Stil in den technischen und tektonischen Kumten, oder praktische Aesthetik (Frankfort, 1860-63); J. Dippel, Handbuch der Aesthetik, etc. (Regensburg, 1871). Among Englishmen, Dugald Stewart, Hutcheson, Alison, Jeffrey, and Payne Knight have written on aesthetics; Burke wrote "A Philosophical Inquiry into the Origin of our Ideas of the Sublime and Beautiful," but the work has little depth. The opposing theories of these older writers have long ceased to attract attention; and, as in Germany, later works on the subject have followed the method a posteriori.

Sir William Hamilton, it is true, in his " Lectures on Metaphysics," considers in the abstract the philosophy of the beautiful; but other recent writers, like Ruskin, whose Aesthetical works are the most voluminous, treat of beauty in form and color. Two recent American works may be also noticed: "The Science of Esthetics," by Henry N. Day (New Haven, 1872), and " Lectures on .Aesthetics," by Professor John Bascom (New York, 1872). One of the best modern writers on Aesthetics is the French critic Hippo-lyte Adolphe Taine, whose principal works on art form a series of essays on the productions of almost every school. See his Philosophie de l'art (Paris, 1865), Philosophie de l'art en Italie (1866), Voyage en Italie (1866), L'Ideal dans l'art (1867), Philosophie de l'art dans les Pays-Pas (1868), etc, translated into English by J. Durand (New York, 1866-70). Among older French writers on Aesthetical subjects are Cousin (Le vrai, le beau et le don) and Jouffroy (Cours d'esthetique, Paris, 1842).