What has been called “the intellectual adventure of the twentieth century” is a sudden awareness of the unexploited possibilities of the arts. It is more than a lucid hubris, more than a deliberate effort to transcend the limits imposed by tradition and prudence. It is a deep conviction that art must change its structure and even its function. All the arts have purified themselves, eliminating the intrusions of other arts; they have rejected everything that was not necessary and vital to their own intentions.