When, one hundred and fifty years ago, Baumgarten wrote the treatise to which he gave the name _Aesthetica_, and which he described as a “theory of liberal arts and beautiful thinking,” it seemed to him needful to apologise for attracting attention to a field of inquiry so low and sensuous as that province of philosophy to which he then affixed a name. Many, he thought, might regard art and beauty, which appeal primarily to the senses, as subjects beneath the dignity of philosophers.[2] Yet the theories and the ideas which were first brought together as an organised body of thought in Baumgarten’s short manual had so deeply influenced the speculations of his age that, a generation later, the most important questions of life came to be treated as æsthetic problems. The philosophy of art, far from needing to justify its existence, dominated all philosophy—ethics, metaphysics, and even cosmogony. Imagination was treated as the ruling faculty in all creation, and beauty was referred to as the criterion, not only in art, but in morality. Yet the importance thus given to æsthetic speculation was transitory, and the period during which philosophers were concerned, not only to find a general criterion of beauty for the arts, but also to apply that criterion far beyond the sphere of art, has been succeeded by an age which neglects speculation on art and beauty for other tasks which are regarded as far more important. Such rapid changes within a few generations appear almost incomprehensible. But they can easily be explained if we take into account the intimate connection which always exists between æsthetic speculation and prevailing currents of thought. In Mr. Bosanquet’s _History of Æsthetic_ it has been pointed out with great clearness to what extent the earlier prosperity of æsthetic studies was caused by the general philosophical situation. The theory of æsthetic, as set forth in Baumgarten’s chapter on _cognitio sensitiva_, and further developed in Kant’s _Kritik der Urtheilskraft_, dealt, as is well known, with a form of judgment which is neither purely rational nor purely sensual.[3] In metaphysics, for philosophers who had to struggle with what seemed to them an irreconcilable opposition between reason and the senses, this conception of a mediative faculty must have satisfied a most urgent need. Similarly we may suppose that the ethical observer felt himself emancipated from the narrow antagonism between body and spirit by looking at our actions in the æsthetic way. In proportion, however, as general science has been able to do away with the old dualism of higher and lower faculties, the judgment of taste has necessarily lost importance. In the development of monistic philosophy and monistic morals we may thus see one important factor, by the influence of which æsthetic has been ousted from its central position.