In his reiterated insistence on Invention and Imagination as the prime endowments of a poet, Keats closely echoes Joseph Warton's protest uttered seventy years before: is this because he had read and remembered it, or only because the same words came naturally to him in pleading the same cause? When his task was finished he confessed, in the draft of a preface afterwards cancelled,--'Before I began I had no inward feel of being able to finish; and as I proceeded my steps were all uncertain.' But so far as the scale of the poem was concerned he adhered almost exactly to his original purpose, dividing it into four books and finding in himself resources enough to draw them out, all except the first, to a little over a thousand lines each.
Throughout Keats's work, the sources of his inspiration in his finest passages can almost always be recognized as dual, some special joy in the delights or sympathy with the doings of nature working together in him with some special stimulus derived from books. Of such a dual kind is the whole inspiration of _Endymion_. The poem is a joint outcome of his intense, his abnormal susceptibility to the spell of moonlight and of his pleasure in the ancient myth of the loves of the moon-goddess Cynthia and the shepherd-prince Endymion[1] as made known to him through the earlier English poets.
The moon was to Keats a power very different from what she has always been to popular astrology and tradition. Traditionally and popularly she was the governess of floods, the presiding planet of those that ply their trade by sea, river, or canal, also of wanderers and vagabonds generally: the disturber and bewilderer withal of mortal brains and faculties, sending down upon men under her sway that affliction of lunacy whose very name was derived from her. For Keats it was her transmuting and glorifying power that counted, not her pallor but her splendour, the magic alchemy exercised by her light upon the things of earth, the heightened mystery, poetry, and withal unity of aspect which she sheds upon them. He can never keep her praises long out of his early poetry, and we have seen, in '_I stood tiptoe_,' what a range of beneficent activities he attributes to her. Now, as he settles down to work on _Endymion_, we shall find her, by reason of that special glorifying and unifying magic of her light, become for him, at first perhaps instinctively and unaware, but more and more consciously as he goes on, a definite symbol of Beauty itself--what he calls in a letter 'the principle of Beauty in all things,' the principle which binds in a divine community all such otherwise unrelated matters as those we shall find him naming together as things of beauty in the exordium of his poem. Hence the tale of the loves of the Greek shepherd-prince and the moon-goddess turns under his hand into a parable of the adventures of the poetic soul striving after full communion with this spirit of essential Beauty.