The basic idea in keats's Ode to A Nightingale is the conflict between the Ideal and the Real, time and timelessness, mortality and an escape into permanence. The real world for keats is conditioned by flux and mutability, an awareness of which causes pain. This notion of mutability and the anguish resulting from it is explored in all details in stanza 3 where Keates avers that human life, health, beauty and love are all subject to flux and hence result in pain:
The weariness, the fever, and the fret
Here, where men sit and hear heach other groan;
Where palsy shakes a few, sad, last gray hairs,
Where youth grows pale, and specter-thin, and dies;
Where but to think is to be full of sorrow
And leaden-eyed despairs.
The Nightingale's song to keats becomes a potent symbol of his nympholeptic longing for immortality and hence his desire for the rapport with the bird. It is not the biological species that is Keats's concern, but the deathless song it produces. The song appaers to the poet to be too full of the spiriot of unadulterated joy and hence the poet's interest in the song. He achieves a rapport with the bird "through the wings of poesy''. it is tragically paradoxical that ultimately the imaginative union with the bird braks and the poet is back to his desolate self;
Adieu the fancy cannot cheat so well
As she is famed to do, deceiving elf.
The poem raises deeply tragic questions relating to the possibility of attainment of immortality or the transcendence of pain in the human condition.