Much like other Romantic poets, John Keats seeks solace in his poetry. His ode, or elaborate lyric poem expressive of exalted emotion, addresses the solace and transience of nature, along with mortality. With his address to the nightingale, Keats enters what Romantics termed the state of Negative Capability,
the human capacity to transcend every given context by negating it in thought or deed.
Negative capability describes the ability of the individual to perceive, think, and operate beyond confining social contexts.
When the poet hears the nightingale singing, he is at first filled with ambivalent feelings. Addressing the bird as is customary in an ode, the poet appreciates the beauty of the bird and its enthusiastic song celebrating life; however, at the same time, he is preoccupied with his moribund state,
Where but to think is to be full of sorrow
And leaden-eyed despairs,
It is in Stanza 4 that Keats initiates the state of Negative Capability: If he cannot transcend mortality by creating flight in the fancy of imagination--even to the point of having the reader accompany him in this transience. It is here that Keats achieves what is quintessentially Romantic. However, he is unable to sustain this apex of romantic imagination as his imminent mortality intrudes,
I cannot see what flowers are at my feet,
Nor what soft incense hangs upon the boughs,
But, in embalmèd darkness, guess each sweet
Wherewith the seasonable month endows
Then, in Stanza 6, the poet declares that, after all, he has been "half in love with easeful Death" as he has hoped for surcease from his agonizing pain; for, it seems "rich to die" accompanied by the "high requiem of the bird. Thus, a sense of Beauty overcomes every other consideration, even the moribund.
Then, in the final stanzas, Keats addresses the bird as "Immortal Bird" in a quasi-religious experience that leaves the poet puzzled about whether he has been awake or sleeping. Nevertheless, Keats continues the conceit, an extended metaphor of the nightingale being an immortal bird that has passed through the ages.
Among the poetic devices that Keats employs is dazzling imagery; in fact the imagery is so exquisite that the reader is entranced by it. One such example of this magnificent imagery is from Stanza 5:
White hawthorn, and the pastoral eglantine;
Fast fading violets cover'd up in leaves;
And mid-May's eldest child,
The coming musk-rose, full of dewy wine,
The murmurous haunt of flies on summer eves.
Indeed, Keats's "Ode to a Nightingale" is truly a transcendental experience.