The paradox attending Wagner's attempt to limn the structural principles of his ideal musical drama in Part III of Opera and Drama is that these principles had as yet no empirical artistic object. The haziness of so many of the theoretical prescriptions in the Zurich writings is a consequence not only of Wagner's overwrought prose style, but also of the peculiar context of these writings in the creative vacuum of the early years of exile. As has often been pointed out, the ideas of Opera and Drama are awkwardly situated between the “no longer” of Tannhäuser and Lohengrin and the “not yet” of the Ring. The shadowy nature of this “theory,” then, is explained to some extent by the fact that it is a theory of non-existent works, unrealized ones: Siegfrieds Tod and Wieland der Schmied. (The abortive musical sketches for Siegfrieds Tod from 1850 are a logical counterpart to the hazy theory of the contemporary essays, not so much because composition couldn't proceed for lack of theory, but the reverse: Wagner couldn't offer a fully coherent, detailed “theory” of works that he had yet to compose.) While Wagner did have in the text of Siegfrieds Tod a concrete object for his observations on Stabreim – however fanciful they may sound – he had none as yet for the specifically musical component of his proposals, most prominently the embryonic theory of “leitmotifs” (the motives of “anticipation” and “reminiscence” expounded in sections five and six of Part III of Opera and Drama) and the concept of a “poetic-musical period” proposed in section three.