The cause of the production of a work of art may indeed by found by tracing back the stream of thought; but the cause of its beauty is the desire and the sense of beauty in the human heart. If a given combination of lines and colors is beautiful, then the anticipation of the combination as beautiful is what has brought about its incarnation. The artist's attitude toward his vision of beauty, and the art lover's toward that vision realized, are the same. The only legitimate aesthetic analysis is, then, that of the relation between the aesthetic object and the lover of beauty, and all the studies in the psychology of invention--be it literary, scientific, or practical invention--have no right to the other name. Aesthetics, then, is the science of beauty. It will be developed as a system of laws expressing the relation between the object and aesthetic pleasure in it; or as a system of conditions to which the object, in order to be beautiful, must conform. It is hard to say where the task of the aesthetician ends, and that of the critic begins; and for the present, at least, they must often be commingled. But they are defined by their purposes: the end and aim of one is a system of principles; of the other, the disposal of a given work with reference to those principles; and when the science of aesthetics shall have taken shape, criticism will confine itself to the analysis of the work into its aesthetic elements, to the explanation (by means of the laws already formulated) of its especial power in the realm of beauty, and to the judgment of its comparative aesthetic value.