first the idea entered my brain," the narrator writes, "but once conceived, it haunted me day and night. Object there was none. " The narrator begins by writing that he had no reason, no "object," for killing the old man, even while he explains why he killed him.

"Passion there was none," he writes, although, as the story unfolds, it's apparent that he's passionate about killing the old man who he also admits he loves but whose declaration of love is negated by the fact that he kills him.

The narrator notes, "He had never given me insult," although it's evident from his act of killing the old man that the narrator took offense at something that prompted the narrator to kill him.

I think it was his eye! yes, it was this! He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye forever.

There it is. The reason that the narrator kills the old man is to rid himself of what he later calls the old man's "Evil eye."

Or is it the reason he kills him?

As the story unfolds, the narrator seems to forget about the old man's "Evil eye," his "vulture eye," and becomes increasingly obsessed with the old man's beating heart. At first, the old man's heart makes just a "low, dull, quick sound, such as a watch makes when enveloped in cotton," but the sound of the old man's beating heart grows increasingly louder, to a "hellish tattoo," and the narrator becomes increasingly terrified and increasingly furious at the sound.

But the berating grew louder, louder! I thought the heart must burst. And now a new anxiety seized me—the sound would be heard by a neighbour!

It's virtually impossible that a neighbor would hear the old man's beating heart, but with that irrational thought in his mind, and with the uncontrollable rage he feels toward the old man's beating heart, the narrator leaps out of hiding and into the old man's room. He drags the old man to the floor, and pulls his heavy bed over him, crushing and suffocating him. It's only then, after the old man's heart stops beating and he's dead, "stone dead," that the narrator again mentions the old man's "Evil eye."

His eye would trouble me no more.

Ridding himself of the old man's "vulture eye" might have provided the initial motivation for the narrator to kill him, but it seems more like an afterthought now that the old man is dead. It's the old man's beating heart which ultimately enrages the narrator to such an extent that he commits murder, and it's the beating of the old man's heart that the narrator hears even after the old man's death that ultimately leads him to shout out his confession of the murder.

After all, Poe titled the story "The Tell-Tale Heart," not "The Evil Eye."

The narrator himself isn't entirely sure why he killed the old man. In fact, he begins by admitting that he isn't sure "how first the idea entered [his] brain." He goes on to concede that he loved the old man and that there wasn't any particular animosity between them. The narrator claims he never wanted the man's money, and then he seemingly tries to convince himself that the old man deserved death because of his eye:

I think it was his eye! yes, it was this! One of his eyes resembled that of a vulture—a pale blue eye, with a film over it.

The narrator seems to stumble on a justification, using exclamations to mark his emotional response to discovering a "valid" reason for his murderous acts.

Of course, the true reason that the narrator kills the old man is because he is mad. In the first sentence, he seems to be responding to some accusation that he is not sane:

TRUE!—nervous—very, very dreadfully nervous I had been and am; but why will you say that I am mad?

He then references a "disease" which has made his senses even more acute. His protests that he is not actually mad are full of indignation, yet any rational reader will realize that sane men do not commit murder over the appearance of an eye. In the end, the narrator also "hears" the heartbeat of the man whom he has killed, which is further indication of his disconnect with sanity. He is so convinced that the now-dismembered man's heart is still beating that he confesses to his crime.

While the narrator believes that he has killed the old man in order to forever rid himself of the man's "vulture" eye, his actions are actually a reflection of his madness.

Simply put, the narrator is crazy. A more developed answer might be, the narrator is unbalanced. Because he thinks he can hear the old man's heart, he thinks others can too. Therefore, he kills the old man to protect himself from being discovered. This can be seen in this passage: " But the beating grew louder, louder! I thought the heart must burst. And now a new anxiety seized me—the sound would be heard by a neighbour!"

This is a straightforward question which even the narrator cannot answer with clarity. He isn't sure how the idea of murder first came to him and admits that he "loved the old man." The old man had never committed any transgressions against the narrator, and he didn't want the man's money.

The narrator seems to stumble upon his reasoning for murder almost by accident:

I think it was his eye! yes, it was this! One of his eyes resembled that of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye for ever.

With the narrator's inclusion of thinking it was the eye that drove him to murder, followed by the exclamation, it seems that he is trying to convince himself of his motives. Of course, people don't murder others because of an odd-looking eye, so all of this together can only mean one thing: the narrator is not mentally stable.

Therefore, the real reason for murder is that these are the actions of an insane man. Although he tries to convince his audience from the first lines that he is sane, there is no support for sanity in his actions. In fact, his subconscious eventually catches up with him in the end, and he admits to the murder because he is convinced that the heart of the man he has dismembered beats loudly underneath the floor where he is hidden.

The narrator's unstable mental abilities are the ultimate source of his desire to murder a man whom he claims he loved.

In Poe's celebrated short story "The Tell-Tale Heart," the mentally deranged, unreliable narrator attempts to convince the audience that he is sane while he vividly describes how he murdered and dismembered an old man. The narrator admits that the old man's pale blue eye motivated him to commit the violent crime. The narrator describes the old man's eye as being evil and is preoccupied with the idea of destroying the "vulture" eye at all costs. Whenever the narrator sees the old man's evil eye, he becomes incensed with rage and his blood runs cold. The reasoning behind the narrator's motivation to kill the old man is perplexing and unsettling, and it completely undermines his argument that he is sane.

The audience recognizes that the narrator is mentally ill and that his argument involving the old man's pale eye is a ridiculous, irrational reason to commit murder. Nonetheless, the narrator is determined to prove his sanity by describing the careful precautions he took before executing the violent crime. The narrator proceeds to peek into the old man's room each night but is not able to commit the crime, because his eye is closed. On the eighth night, the narrator finally looks into the old man's evil eye and attacks him. After smothering the old man to death, the narrator dismembers his body and hides his remains underneath the floorboards. However, the narrator is not able to maintain his composure in front of the police and eventually admits to murdering the old man.

A very good question, and one which the narrator of the story cannot really answer, although it seems he has wrestled with it. Note that the narrator continually toys with, and then rejects, the idea that he is "mad," and that it is this "disease" that has led him to do what he has done. As a reader, we can determine that this is probably the case—after all, the narrator says there was no "object" to his killing of the old man, whom he loved, and he could not say when the thought first entered his mind. The only thing he can think is that the old man's pale, filmy, blue eye, which made him feel judged or unhappy whenever it landed upon him—he calls it the eye of a "vulture"—drove him to kill the old man. He couldn't stand being looked at by that terrible eye which made his "blood [run] cold," and eventually this preoccupation led him to murder the man, just so that he could escape the eye.

Ultimately, of course, he does not escape anything—the murder of the old man is only the beginning of the narrator's problems, as the story tells.

As the narrator mentions, he has no explicit reason for killing the old man. No relationship between them is mentioned; he is possibly the old man's son or nephew, or a live-in caretaker. Of course, it must be remembered that the narrator is unreliable; despite his protestations to the contrary, he is clearly insane to some degree, and possibly also delusional (one interpretation is that he never killed the old man at all, and that is why there is no blood). In the opening, he states:

It is impossible to say how first the idea entered my brain; but once conceived, it haunted me day and night. Object there was none. Passion there was none. I loved the old man. He had never wronged me. He had never given me insult. For his gold I had no desire. I think it was his eye! yes, it was this!(Poe, "The Tell-Tale Heart")

The narrator is suffering from an extreme version of morbid irritation; he finds the presence of the old man's "vulture eye" intolerable, and instead of searching for other employment or other living circumstances, he decides that the only rational solution is to murder the old man, thus ridding himself of the "vulture eye." His focus is on the eye itself, as he is unable to kill the old man until the eye is open and visible. However, considering how unreliable he is, it is impossible to say that greed or some other justification is not responsible for his actions.

The narrator is insane and believes that the old man has an evil force present within him, in his eye. 

"for it was not the old man who vexed me, but his Evil Eye."  

The Evil Eye is a belief that others had the ability to transmit curses with their eyes.  Its purpose was to cast a spell of bad luck, disease or death upon its victim.  

"It was open—wide, wide open—and I grew furious as I gazed upon it. I saw it with perfect distinctness a dull blue, with a hideous veil over it that chilled the very marrow in my bones; but I could see nothing else of the old man's face or person:"   

The narrator may very well have been cursed by the old man's Evil Eye.  After the murder, the narrator, who believes he has gotten away with the murder is haunted with a terrible sensation that he cannot ignore.

"My head ached, and I fancied a ringing in my ears: but still they sat and still chatted. The ringing became more distinct:—It continued and became more distinct:"

The torment that he faces grows and grows within him until he can no longer stand it.

"It grew louder—louder—louder! And still the men chatted pleasantly, and smiled. Was it possible they heard not? Almighty God!—no, no! They heard!—they suspected!—they knew!—they were making a mockery of my horror!"

The old man has beaten the narrator at his own game.  

The narrator decides to kill the boarding house owner because of his strange, milky-colored eye (most like a cataract-covered eye).  This eye becomes the obsession of the narrator and he decides that he must kill the boarding house owner.  He boasts of his own cleverness and he stalks the owner. He watches him without moving an inch as he sleeps at night.  The reader knows early on that the narrator is clearly mentally ill, obviously. 

Once the narrator murders the owner, he dismembers his body and puts it underneath the floorboards.  When the police come to question him about the murder, the narrator begins to hear what he perceives to be a heartbeat (probably the beating of his own heart). This causes him to become nervous and eventually paranoid.  He finally cannot take it anymore and he screams that he killed the owner of the boarding house.

The narrator simply killed the owner for no other reason except the strange eye.  The narrator even points out the the owner was a kind man who he got along with well. 

Poe's classic short story "The Tell-Tale Heart" is told by an unreliable narrator, who is clearly mentally unstable. There are numerous clues that suggest the unreliable narrator is insane, which include his continual insistence that he is not "mad," his staccato writing style, and his "sharpened" senses that allow him to hear paranormal sounds. Toward the beginning of the story, the narrator mentions that he had no ill will toward the old man and actually loved him—another example of his insanity. After reading this statement, the reader cannot help but wonder how someone could murder a person they love. The narrator goes on to say that he was not motivated by money to kill the old man and was simply disturbed by the old man's "Evil eye." The insane narrator explains his reason for killing the old man by saying,

I think it was his eye! yes, it was this! He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees —very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye forever. (Poe, 1)

One could argue that the narrator's desire to murder the old man stems from his mental instability. He is clearly mentally ill, and his motivation to kill the old man is not a strong enough reason to commit such a horrific crime, in the eyes of most people. Therefore, one could surmise that the narrator murdered the old man because he was mentally ill and insane.

To answer this question, take a look at the second paragraph of the story. According to the narrator, the old man had an "evil eye" which made him feel very uneasy:

He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold.

In other words, the narrator felt compelled to kill the old man because this was the only way that he could stop the evil eye from bothering him. As a result, he immediately made plans to murder the old man.

However, if we look a little deeper, it becomes clear that the narrator killed the old man for another reason. Specifically, we can argue that the narrator killed the old man because the narrator was not of sound mind. In the week preceding the murder, he was clearly suffering from some kind of mental illness which caused a deep sense of paranoia about the old man. Although the narrator opens the story by claiming that he is not mad, his motivation for the murder suggests otherwise.

The answer to this question can be found pretty quickly in the beginning of the story itself, if you read closely.  The narrator, widely assumed to be a man, states in the second paragraph rather plainly that he had no real motive for killing the old man.  He tells us that

"Object there was none.  Passion there was none.  I loved the old man.  He had never wronged me.  For his gold I had no desire."

So, the old man had never made him upset, so he didn't want to kill him out of revenge or anger.  The narrator also says he didn't want to steal the old guy's money, and there was no "object" or purpose for his motives.  No passion, no intensity of hatred against the poor guy.  Then, he gives what is possibly the strangest reason in any murder tale, for wanting to kill the old man.  The narrator says it was because

"He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye forever."

Bizarre reason to kill someone, if you ask me.  The old guy's eye bothered him.  Maybe the man was blind, or had an eye condition, but it looked a bit creepy--milky, with a film over it, and that eye bothered the narrator so much that whenever he saw it it made his blood run cold. So, his obvious conclusion is that he must kill the old guy, just to get rid of the eye.  It's an interesting reason, one that begs the question of the narrator's sanity.  I hope that helps a bit; good luck.

The narrator actually likes the old man.  He says in the second paragraph of the story that he had nothing against the old man.  This was not a crime of passion or one of insult.  In fact, he says,

"I loved the old man." (page 1, paragraph 2)

Then he says,

"I think it was his eye! -----yes, it was this!  He had the eye of a vulture ---- a pale,blue eye, with a film over it.  Whenever it fell upon me, my blood ran cold; and so, by degrees --- very gradually ---- I made up my mind to take the life of the old man, and thus rid myself of the eye forever!" ( paragraph 2)

This reasoning, this logic, is what signals for the reader that the man really is insane.  Poe even plants the seed in the reader's mind when in the first paragraph he says

 ".....but why will you say that I am mad?" ( paragraph 1)

After he kills the old man, the narrator brags about how clever he was in concealing the old man's body.

"First of all, I dismembered the corpse.  I cut off the head and the arms and the legs.  I then took up three planks from the flooring of the chamber, and deposited all between the scantliings.  I then replaced the boards so cleverly, so cunningly, that no human eye ----not even his --- could have detected anything wrong." (paragraph 12) There was........no bloodspot whatever. ...A tub had caught all ---ha! ha!

In other words, he cut the body up in a tub so that blood wouldn't go anywhere.  He cut off the head, the arms, and the legs.  He then pulled up three boards from the floor in the bedroom and put the body parts in the structure of the bedroom.  He then cleverly put the boards back and was really impressed with his work.  He said no one would ever be able to tell that anything was below the boards.  

This is a story in which the doppelganger, or double, is key. Poe has the narrator say a number of things that point to his identification with the old man. Even the apparently random 'eye' the narrator gives as his reason for the murder is a homonym of 'I', and so the narrator can in a real sense be seen to be killing the old man in an act of loathing directed at himself.

Although there is no specific reason given for the narrator's murdering of the old man, it seems as though there is some severe psychological problem present.  Although it is just a guess, it sounds a little like paranoid schizophrenia.

For an unknown reason, the old man's cloudy, pale blue eye has incited madness in the narrator. Whenever the old man looks at him, his blood turns cold. Thus, he is determined to kill him to get rid of this curse.

The exact reason due to which the narrator kills the old man in Edgar Allan Poe’s The Tell-Tale Heart is not very well understood or clear. The narrator himself is not sure what invoked the idea of killing the old man.

It is impossible to say how first the idea entered my brain; but once conceived, it haunted me day and night.

Since there is no exact reason behind the murder, we are bound to think that, perhaps, the narrator is insane or some kind of a psycho-killer. The narrator, however, insists in the first few lines that he is not mad since he carefully planned the murder with such precision. But, of course, this explanation is not very convincing.

TRUE!—NERVOUS—VERY, very dreadfully nervous I had been and am; but why will you say that I am mad?

The narrator says that he had no real issue with the old man and, in fact, he loved him. He also mentions that the old man never did anything wrong with him and never ever insulted him. The old man was quite wealthy, but the narrator said that he was not interested in his wealth also.

He had never wronged me. He had never given me insult. For his gold I had no desire.

So why would the narrator kill him? The narrator does point out that he did not like the old man’s eyes. He got uncomfortable and nervous when he saw his pale, blue eyes like that of a vulture. He claims that he wanted to just get rid of those eyes.

I think it was his eye! yes, it was this! He had the eye of a vulture—a pale blue eye, with a film over it. 

A reason like this to murder someone is not justified. Only someone really mad would think like that. The narrator kills the old man very brutally. In fact, just note the way the narrator handles everything with the policemen after he murders the old man. All this also give a hint that the narrator is an unbalanced, impatient and insane person.

The narrator repeatedly tries to explain that an insane person cannot do such a calculated murder and this makes him absolutely normal. But we are forced to think that the narrator is, indeed, crazy. So, we can say that the narrator killed the old man because he is mad. The poor old man was misfortunate to have become the target of the narrator’s madness.