In "The Tell-Tale Heart," is the narrator considered reliable or unreliable?
The narrator of "The Tell-Tale Heart" is unreliable. He is trying from the very beginning of the story to make a case for his sanity, but the very story he tells completely undermines and is at odds with his assertions of sanity. Throughout his narrative, he recalls the events that led him to murder the old man and then confess. He attempts to illustrate his clearheaded reasonableness with examples. For instance, he tells us that he "loved the old man" and that the old man had never wronged him. This admission makes his murder of the man less, rather than more, understandable or sane. Why would you murder someone you loved who had done you know wrong—and merely over his eye, as the narrator insists is the case?
He also asserts that he cannot be mad for the following reason:
Now this is the point. You fancy me mad. Madmen know nothing. But you should have seen me. You should have seen how wisely I proceeded—with what caution—with what foresight—with what dissimulation I went to work!
Yet, we know that madmen can be quite knowledgeable—and can proceed with caution and foresight. The narrator completely misses the point while thinking he is making a valid point: it is not how he proceeded but what he did—murdering an innocent man for no good reason—that attests to his lack of mental stability.
Finally, he hears the dead man's heart beating at the end, probably a manifestation of his own guilt. Yet, rather than assume he might be hearing things or hallucinating, the narrator violently insists that the police are mocking him:
They heard! —they suspected! —they knew! —they were making a mockery of my horror!—this I thought, and this I think.
The disjunction between what happens and how the narrator interprets it leads us to conclude he is unreliable.
The narrator is a classic example of an unreliable narrator, because he is telling the entire story himself and there is no objective narration to back up his assertions. The first lines of the story show this, as the narrator is trying to explain that he is not mad, that he is perfectly sane, only that he is in the throes of some unnmamed illness that heightens his senses:
...why will you say that I am mad? The disease had sharpened my senses --not destroyed --not dulled them... How, then, am I mad? Hearken! and observe how healthily --how calmly I can tell you the whole story.
(Poe, "The Tell-Tale Heart," xroads.virginia.edu)
A reliable narrator would not be pressed to justify his act, but only to tell it simply and without embellishment. Since this narrator cannot explain his actions without constantly explaining himself, he can't be fully trusted; furthermore, his later mental breakdown as he imagines the beating of the old man's heart shows that his mind is not healthy. If the story is taken allegorically, it is possible that the crime was imaginary and the narrator explaining his motivations in a sanitarium. In this story, the unreliable narrator is the key to both the crime itself and its solution; had the narrator had less guilt, and more mental stability, he might have gotten away with the murder much as Montresor did in Poe's "The Cask of Amontillado."