In this theory Schopenhauer starts from Plato's doctrine of the Ideas. The particular objects of sense, which we know, are mere appearances. They have no reality in themselves. They arise and pass away, they always become and never are. But there exist also the types and eternal forms of things, which do not enter into time and space, and which remain fixed, subject to no change. These constitute the sole reality. Plato called them the Ideas, and Schopenhauer adopts this term from the Platonic philosophy. The Ideas for Schopenhauer represent the different grades of the objectification of the will, which are manifested in the individuals. These are the eternal forms or prototypes of individual things. Our knowledge of the ordinary things of sense-experience is indirect, it is gained by way of the intellect. Our knowledge of the Ideas, on the other hand, is direct and immediate, it is gained through intuition. In his account of the Ideas, or the real, essential nature of things, Schopenhauer is treading already the path of mysticism, along which he works out his theories of ethics. Now the whole function of art is to reproduce the eternal ideas, to seize on that which is essential and abiding in all the phenomena of the world. The one and only source of art is the knowledge of true reality, of the Ideas. The one aim of art is the communication of this knowledge. According to the material in which this vision of true reality is reproduced, it is architecture, sculpture, painting, poetry, or music. {54} Science can only follow the unresting and inconstant stream of appearances. It can never reach a final goal nor attain complete satisfaction, any more than by running we can reach the place where the clouds touch the horizon. But art, on the other hand, is everywhere at its goal. It plucks the object of its contemplation out of the stream of things as they seem, and holds it isolated before its vision. And this particular thing, which in the stream of the world's course was a small perishing part, becomes to art the representative of the whole, the type of the endless multitude in space and time. Art, therefore, pauses before this reality, which it perceives in the particular thing. The course of time stands still; relations vanish before it; only the essential, the Idea, remains as the object of the artist's vision. In the multitudinous and manifold forms of human life, and in the unceasing change of events, the artist looks only on the Idea, knowing it as the abiding and the essential, as that which is known with equal truth for all time. Art, therefore, is the bridge between two worlds. It leads us from things as they seem to things as they really are. It is the genius who possesses this power of vision, and whose magic works can unfold before the eyes of ordinary mortals the spirit of beauty as she has revealed herself to him. Entirely in this spirit does Blake express his sense of the poet's mission: