Schiller was well aware that the moment art is employed to teach morals directly, it ceases to be art. All other teachings give to the soul a special imprint. Art alone is favourable to all without prejudice. Owing to this indifference of art, it possesses a great educative power, by opening the path to morality without preaching or persuasion; without determining, it produces determinability. This was the main theme of the celebrated "Letters on the Aesthetic Education of Man," which Schiller wrote to his patron the Duke of Holstein-Augustenburg. Here, and in his lectures at the University of Jena, it is clear that Schiller addresses himself to a popular audience. He began a work, on scientific Aesthetic, which he intended to entitle "Kallias," but unfortunately died without completing it. We possess only a few fragments, contained in his correspondence with his friend Körner. Körner did not feel satisfied with the formula of Schiller, and asks for some more precise and objective mark of the beautiful. Schiller tells him that he has found it, but what he had found we shall never know, as there is no document to inform us. The fault of Schiller's aesthetic theory was its lack of precision. His artistic faculty enabled him to give unsurpassable descriptions of the catharsis and of other effects of art, but he fails to give a precise definition of the aesthetic function. True, he disassociates it from morality, yet admits that it may in a measure be associated with it. The only formal activities that he recognizes are the moral and the intellectual, and he denies altogether (against the sensualists) that art can have anything to do with passion or sensuality. His intellectual world consisted only of the logical and the intellectual, leaving out the imaginative activity. What is art for Schiller? He admits four modes of relation between man and external things. They are the physical, the logical, the moral, and the aesthetic. He describes this latter as a mode by which things affect the whole of our different forces, without being a definite object for any one in particular. Thus a man may be said to please aesthetically, "when he does so without appealing to any one of the senses directly, and without any law or end being thought of in connection with him." Schiller cannot be made to say anything more definite than this. His general position was probably much like Kant's (save in the case above mentioned, where he made a happy correction), and he probably looked upon Aesthetic as a mingling of several faculties, as a play of sentiment. Schiller was faithful to Kant's teaching in its main lines, and his uncertainty was largely due to this. The existence of a _third sphere_ uniting form and matter was for Schiller rather an ideal conformable to reason than a _definite_ activity; it was supposititious, rather than effective.