Midway through the poem, there is a split between the two actions of the poem: the first attempts to identify with the nightingale and its song, and the second discusses the convergence of the past with the future while experiencing the present. This second theme is reminiscent of Keats's view of human progression through the Mansion of Many Apartments and how man develops from experiencing and wanting only pleasure to understanding truth as a mixture of both pleasure and pain. The Elysian fields and the nightingale's song in the first half of the poem represent the pleasurable moments that overwhelm the individual like a drug. However, the experience does not last forever, and the body is left desiring it until the narrator feels helpless without the pleasure. Instead of embracing the coming truth, the narrator clings to poetry to hide from the loss of pleasure. Poetry does not bring about the pleasure that the narrator original asks for, but it does liberate him from his desire for only pleasure. 
An Essay on Criticism is one of the first major poems written by the English writer Alexander Pope (1688–1744). It is the source of the famous quotations "To err is human, to forgive divine," "A little learning is a dang'rous thing" (frequently misquoted as "A little knowledge is a dang'rous thing"), and "Fools rush in where angels fear to tread." It first appeared in 1711  after having been written in 1709, and it is clear from Pope's correspondence  that many of the poem's ideas had existed in prose form since at least 1706. Composed in heroic couplets (pairs of adjacent rhyming lines of iambic pentameter ) and written in the Horatian mode of satire, it is a verse essay primarily concerned with how writers and critics behave in the new literary commerce of Pope's contemporary age. The poem covers a range of good criticism and advice, and represents many of the chief literary ideals of Pope's age.