"Webster-Miriam" defines 'Vision' as something seen in a dream, trance, or ecstasy; especially: a supernatural appearance that conveys a revelation. Keats describes in his poem that he doesn't know if the song of the bird was something in reality or something that he conjured up in his mind. The poem itself is almost trance-like; the basic rhyme scheme allows the reader to flow along with the poet and join in the song of the Nightingale. Keats 'vision' allows him to look upon the frailty and mortality of mankind and delve deeper into the themes of death, pain and sorrow.