In the 1922 preface to "The Trembling of the Veil" Yeats writes of a Sacred Book which the generation of the '90's had sought unsuccessfully to bring forth; in 1925 he published A Vision, the writing of which he publicly associated with the search for a Sacred Book. For Yeats the Sacred Book represented the embodiment of the absolute unity of form and content, of image and ideal. During the 1890's, the idea of such a book had shaped both his aesthetic philosophy and his own writing; why, then, should Yeats have resurrected this symbol as part of a public framework and reference to A Vision (1925)? What can we learn about Yeats's earlier conception of the Sacred Book that may shed light upon the aesthetic contexts within which he developed A Vision? If the following study is a work of literary criticism, its subject is a text that could not be written, and the influence of this text upon the writing of W. B. Yeats.