In the midst of these aesthetic studies, and while producing his own greatest works, Shelley was not satisfied that his genius ought to be devoted to poetry.  “I consider poetry,” he wrote to Peacock, January 26th, 1819, “very subordinate to moral and political science, and if I were well, certainly I would aspire to the latter; for I can conceive a great work, embodying the discoveries of all ages, and harmonizing the contending creeds by which mankind have been ruled.  Far from me is such an attempt, and I shall be content, by exercising my fancy, to amuse myself, and perhaps some others, and cast what weight I can into the scale of that balance which the Giant of Arthegall holds.”  Whether he was right in the conviction that his genius was no less fitted for metaphysical speculation or for political science than for poetry, is a question that admits of much debate. (See Mrs. Shelley’s note on the Revolt of Islam, and the whole Preface to the Prose Works.) We have nothing but fragments whereby to form a definite opinion—­the unfinished “Defence of Poetry”, the unfinished “Essay on a Future State”, the unfinished “Essay on Christianity”, the unfinished “Essay on the Punishment of Death”, and the scattered “Speculations on Metaphysics”.  None of these compositions justify the belief so confidently expressed by Mrs. Shelley in her Preface to the prose works, that “had not Shelley deserted metaphysics for poetry in his youth, and had he not been lost to us early, so that all his vaster projects were wrecked with him in the waves, he would have presented the world with a complete theory of mind; a theory to which Berkeley, Coleridge, and Kant would have contributed; but more simple, and unimpugnable, and entire than the systems of these writers.”  Their incompleteness rather tends to confirm what she proceeds to state, that the strain of philosophical composition was too great for his susceptible nerves; while her further observation that “thought kindled imagination and awoke sensation, and rendered him dizzy from too great keenness of emotion,” seems to indicate that his nature was primarily that of a poet deeply tinctured with philosophical speculation, rather than that of a metaphysician warmed at intervals to an imaginative fervour.  Another of her remarks confirms us in this opinion.  “He considered these philosophical views of mind and nature to be instinct with the intensest spirit of poetry.” (Note on Prometheus.) This is the position of the poet rather than the analyst; and on the whole, we are probably justified in concluding with Mrs. Shelley, that he followed a true instinct when he dedicated himself to poetry, and trained his powers in that direction. (Note on Revolt of Islam.) To dogmatize upon the topic would be worse than foolish.  There was something incalculable, incommensurable, and daemonic in Shelley’s genius; and what he might have achieved, had his life been spared and had his health progressively improved, it is of course impossible to say.