What literary devices have been used in "The Black Cat" and how do they explain the themes?

"The Black Cat" incorporates a number of literary devices, including an unreliable narrator, symbolism, and irony, to reinforce its theme that wicked people cannot feel remorse because they do not take responsibility for their actions. 

The unreliable narrator in this story is one of its most ingenious techniques. From the first sentence of the story, we are told by the first-person narrator, "I neither expect nor solicit belief." Mad we would be indeed to give...

"The Black Cat" incorporates a number of literary devices, including an unreliable narrator, symbolism, and irony, to reinforce its theme that wicked people cannot feel remorse because they do not take responsibility for their actions. 

The unreliable narrator in this story is one of its most ingenious techniques. From the first sentence of the story, we are told by the first-person narrator, "I neither expect nor solicit belief." Mad we would be indeed to give it to him then! Therefore the reader must carefully study the narrator's words and read between the lines to find the truth of the tale. The narrator's effusive descriptions of himself in the second paragraph certainly must be taken with a grain of salt; we can see already that before the narrator degenerated into a violent man, he was already incapable of being honest with himself. Throughout the story, every time the narrator has a chance to take full responsibility for what he has done, he either blames something else (alcohol, his "disease," the cat) or he can't quite bring himself to be fully remorseful. Hence we have statements such as, "I blush to confess it," where he doesn't blush at the deed itself, but only at having to confess it, and "I experienced a sentiment half of horror, half of remorse," where he admits he does not feel the full weight of his guilt. Even in the very last line of the narrator's "confession," he notes that it was the cat who "seduced me into murder." Poe expects the reader to see through the narrator's biased interpretation of events and to understand that this wicked man, despite his evil deeds, is still unwilling to fully take responsibility for what he did.

The symbols in the story also point to the man's guilt and the way he continues to explain it away. The bas relief of Pluto that appears after the fire is a symbol of the depravity of the narrator, and that it needs to come to light. However, the narrator is able to come up with an explanation that "readily accounted to my reason, if not altogether to my conscience" of how the relic was created. He is unable to feel complete remorse, indicating he does not accept full responsibility. The second black cat is a symbol, like the first, of the man's guilt and seared conscience. The cat has a blind eye reminiscent of Pluto, and it has a marking on its chest that begins to look more and more like gallows. The narrator despises the cat, showing he has not come to terms with his past sins.

Finally, the narrator seeks to kill the cat, and instead murders his wife. Typical of his inability to own his actions, he hides the body by walling it up in his cellar. But just when it seems that he will once and for all get rid of his conscience and all reminders of his depravity, the cat calls out from behind the brick wall. The irony is  that, although the narrator tried to kill the cat, he doesn't succeed, and the cat ends up giving away the narrator's guilt and sending him to the gallows. This irony reinforces the theme that a wicked person never takes responsibility for his actions, thus requiring outside forces to come into play to hold the person accountable for his evil deeds.