Here's why:
* Poe loved playing with contradiction and paradox: His themes often revolve around the tension between life and death, sanity and madness, beauty and horror. This inherent duality lends itself naturally to oxymoronic phrasing.
* Examples in his stories:
* "The Tell-Tale Heart": The narrator, obsessed with the "vulture eye" of his victim, claims he is "not mad." This is a clear oxymoron, as his actions and statements prove his insanity.
* "The Raven": The poem uses words like "grim, ungainly, ghastly, gaunt" to describe the raven, creating an image of a creature that is both beautiful and terrifying.
* "The Fall of the House of Usher": The house itself is a symbol of decay and ruin, yet it possesses a strange beauty. The description of the house as "a crumbling ruin... of a singular and almost picturesque hideousness" is a prime example of oxymoron.
While Poe may not have formally labeled these instances as oxymorons, he skillfully uses the device to heighten the unsettling and ambiguous atmosphere of his tales.
It's important to note: The impact of oxymoron lies in the juxtaposition of seemingly opposing ideas. Whether Poe intended this as a specific rhetorical device or simply an inherent part of his style is open to interpretation. However, the effect remains undeniable in his work.