What is the theme of The Raven?

At first the narrator attempts to give his experiences a rational explanation, but by the end of the poem, he has ceased to give the raven any interpretation beyond that which he invents in his own head. The raven thus serves as a fragment of his soul and as the animal equivalent of Psyche in the poem "Ulalume." Each figure represents its respective character's subconscious that instinctively understands his need to obsess and to mourn. As in "Ulalume," the protagonist is unable to avoid the recollection of his beloved, but whereas Psyche of "Ulalume" sought to prevent the unearthing of painful memories, the raven actively stimulates his thoughts of Lenore, and he effectively causes his own fate through the medium of a non-sentient animal.