vision of a "dagger of the mind").
Secondly, the visions also serve to show Macbeth's (and Lady Macbeth's) downfall. Macbeth sees a dagger, which becomes bloody; then he sees a ghost. The first vision is private. He is able to keep his thoughts hidden. The latter is public and his immediate court witness his troubled mind. He is able to dismiss the first -- indeed using that wonderful phrase to ask if the vision is a "dagger of the mind." He questions the vision. But when confronted with the vision of the ghost, he is unable to dismiss it willingly. It consumes him; he has fallen, and in a sense in the drama, there is no opportunity for redemption left him at that point.
The visions show Macbeth in relation to temptation and then in relation to sin entertained. He is able to withstand the temptation, and toy with it; but once having sinned, the consequence (and the vision) are irresistible.

Macbeth's visions and hallucinations, in addition to foreshadowing subsequent events in the play, contribute to the development of Macbeth's avarice. He interprets the withces' predictions as supernatural approval for his becoming king. Then, he acts upon his interpretation of their predictions to continue the cycle of murder. Finally, the assurances that no one born of woman will defeat him and that he will be safe until Burnam woods mover to Dunsinane give him false security. The visions and hallucinations contribute to the Macbeth's downfall.

To understand the nature and reason for Macbeth's visions and hallucinations, and how they determine his character, one has to understand the context in which they occur.

It is clear that even though Macbeth has concluded that he has to kill Duncan to become King of Scotland, he does not relish the task. He is overwhelmed by the thought of having to commit such a dreadful act and in a lengthy monologue he reasons that his purpose is too feeble, saying:

I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other.

He has reasoned that there are many reasons why killing Duncan would not be wise. In this state of mind, he tells Lady Macbeth that:

We will proceed no further in this business

He is, however, persuaded by her insistence, her criticism of his manhood and her promise to be cold towards him to continue with the dastardly deed.

It is in this context that Macbeth, when the time nears to commit the foul deed, hallucinates and sees a dagger appear before him. He is under intense pressure, for he has made a vow to his wife. He is anxious, afraid and overwhelmed by the thought of committing such a horrific crime. So overcome is he by all these factors that he imagines seeing the dagger, which is a representation of the evil he is about to commit. Macbeth realises this and questions this figment of his imagination:

art thou but
A dagger of the mind, a false creation,
Proceeding from the heat-oppressed brain?

The second time Macbeth is occasioned by an unwelcome vision is after he has had Banquo murdered. Once again, he has committed an utterly reprehensible act: the assassination of a best friend, confidante and ally. Banquo's ghost appears to him at the banquet table, sitting in his place. Macbeth addresses the spirit he imagines seeing:

Thou canst not say I did it: never shake
Thy gory locks at me.

Macbeth has turned pale with fear and his wife informs the gathering that he is having a fit, an illness that he has had since childhood. Macbeth, however, is horrified and sees the vision as '...that which might appal the devil'. When the ghost reappears, Macbeth is once again overcome with fear and orders the ghost to leave. Once the ghost vanishes he declares,

'Why, so: being gone,
I am a man again'.

It is clear at this point that Macbeth has been, and is, possessed by paranoia - he has begun seeing danger everywhere - there is considerable risk, even from the dead. In this state, he has begun to get rid of those he deems a threat, and no one is spared. Macbeth has now become rooted so much in his own evil that he cannot stop himself.

Finally, Macbeth undertakes a visit to the witches to seek their assurances that he is safe and protected by their charm. During this visit, he sees several visions, each with its own message. The first is the apparition of an armed head which informs him:

... beware Macduff;
Beware the thane of Fife.

The second apparition says the following:

Be bloody, bold, and resolute; laugh to scorn
The power of man, for none of woman born
Shall harm Macbeth.

The third:

... Macbeth shall never vanquish'd be until
Great Birnam wood to high Dunsinane hill
Shall come against him.

The fourth vision is one of Banquo, showing his hereditary line which follows into eternity. Banquo appears at the end. Macbeth is overwhelmed and utters the following:

Horrible sight! Now, I see, 'tis true;
For the blood-bolter'd Banquo smiles upon me,
And points at them for his.

Macbeth has reached a point where he feels so vulnerable that he needs guarantees from the evil sisters that he is safe. Since he mistrusts everyone, he ironically turns to the devil's disciples for comfort. Macbeth has lost all reason and is unable to see through the witches' paradoxes and equivocation. When he is later faced with the reality of their ambiguity, it is too late. He then only realises their deception and finally acknowledges their devastating and diabolical duplicity.

Macbeth is a play about power and the insanity it can bring. We see both Macbeth and Lady Macbeth, lose their grip on reality and it shows up in many forms.

One of the most significant visions we see is when the floating dagger accompanies Macbeth as he goes to murder King Duncan. Even Macbeth questions what he is seeing "Is this a dagger which I see before me?". We can see that Macbeth is having visions and questions the reality of what he is seeing. 

"Art thou not, fatal vision, sensible to feel as to sight? Or art thou but a dagger of the mins, a false creation, proceeding from the heat-oppressed brain?" (Act 2, Scene 2)

The dagger is covered with blood, which represents the bloody course Macbeth and Lady Macbeth are headed down. The dagger is pointing like an arrow at the king's chamber. This is interesting as well, when a person's mind becomes splintered by insanity, sleep becomes useless. King Duncan was killed while he was sleeping restfully, while Macbeth is tormented and can't sleep.

Another example of how madness is shown in visions and not sleeping, is when Lady Macbeth is sleepwalking and has a hallucination of blood stains on her hands. She thinks her hands are covered in the blood of the innocent and she tries to wash it off, but it won't come off. Of course there is no real blood on her hands, but her splintered mind is seeing the blood stains. Both Macbeth and Lady Macbeth slowly slip into madness, and the hallucinations and visions they see show us this.

There are three very notable hallucinations that Macbeth experiences. One is the dagger that he sees floating before him just before he is about to murder Duncan. Just after he kills the king, he fancies he hears voices calling out that 'Macbeth does murder sleep!' (2.2. 33). Later, once he has become king, and arranged for the murder of Banquo, he sees Banquo's ghost. These visions and hallucinations all testify to the fact that he is slowly becoming unhinged. To begin with, he did not really have it in him to murder; he has to force himself to kill Duncan, and his hallucinations just before and after committing this crime demonstrate how disturbed he is over it. Once he begins his path of crime, however, he becomes ever more reckless, killing more and more, but this is essentially out of a sense of increasing despair - he feels he is beyond all salvation and this drives him slowly insane. This also happens to Lady Macbeth: her overriding sense of guilt and remorse manifests itself in her sleepwalking where she obsessively tries to scrub out bloodstains.

In the play Macbeth, reality is often difficult to discern due to the mystical forces that surround the characters. The three witches, who serve not only as a kind of chorus but also as active characters in conversation with Macbeth and others, offer predictions about Macbeth's future. At the start of the play, Macbeth hears their first prophecy about how he will be made Thane of Cawdor and also king, and when he quickly does become Thane of Cawdor, he puts his faith in the witches. This is the first time visions and hallucinations guide Macbeth in his choices. Because of what the witches tell him, he decides he will now move forward and, with the help of his wife, assassinate Duncan in order to become king.

Since the witches also told Macbeth and Banquo (Macbeth's best friend) that he will "get kings," Macbeth believes the safest route is to kill Banquo and his only son, Fleance, to preclude any future rivalry to the throne. Thus, his fate is sealed—especially since his wife takes the witches's words seriously. He does kill Banquo, an ally, and attempts to kill Fleance, but the boy escapes.

Macbeth is also told he should fear MacDuff. This occurs in act 4, scene 1, in which the witches give three prophecies to help comfort Macbeth about the future, but the predictions are so vague and unreal that their interpretation is not really possible. In this scene, a vision appears before Macbeth of eight kings, the last of whom carries a mirror, while Banquo's ghost walks behind them. This vision fills Macbeth with fear, not only because he does not know how to interpret it but also because he feels intense guilt about murdering Banquo. His fear is partly responsible for his decision to send assassins to murder not only MacDuff but also the man's wife and children, thus intensifying the level of brutality.

Toward the end of the play, Macbeth and Lady Macbeth are shored up in their castle, Dunsinane. During a sleepwalking episode, she begins her speech with the notorious quote, "out, damned spot!" because she sees blood where there is none, and she desperately wants the blood to wash out. Her descent into madness and Macbeth's reactions to her visions seal his fate. He no longer cares about her, although he desperately tries to get help from a doctor to cure her hallucinations. These delusions affect Macbeth deeply, as he loses the only real support he'd ever had in Lady Macbeth.

Macbeth's initial visual hallucination—a dagger that becomes bloody when he looks away and then back at it—betokens his extreme duress and internal conflict over killing Duncan. He has outlined the many reasons he has not to go forward with the murder; Duncan is his king, his cousin, his friend, his guest, a really good person and humble ruler to boot. Only his ambition and, later, his pride, which is wounded by his wife's insults and criticisms of his cowardice and indecision, compel him to move forward with the plan. The unbloodied dagger seems to represent Macbeth's final opportunity to turn back, but when he sees it dripping with gore, it spurs him onward, and he interprets it as a symbol of the deed he's about to do.

Immediately after the murder, Macbeth has an auditory hallucination when he hears voices that cry out, "Macbeth shall sleep no more." He has murdered a man while that man slept, an unnatural act anyway considering sleep's purposes in restoring and reviving us. It soothes us and serves to lessen our cares. This hallucination betokens Macbeth's terrible guilt for killing Duncan. He knows he has done something terrible—for several reasons—and this weighs heavily on his conscience. Notice that he does not have hallucinations following the murder of Banquo or Macduff's family, and this indicates his waning guilt; his conscience is bothered less and less by his heinous actions as the play progresses. (I do not consider the ghost of Banquo to be a hallucination because the ghost has stage direction. Macbeth must narrate his hallucination of the dagger because we cannot see it; he must tell us what he sees. However, we can see the ghost, and I believe that this indicates that it is truly there and not only in his mind.)

In Macbeth, Macbeth's visions and hallucinations serve as symbols of Macbeth's inner conflict throughout the play.  Macbeth has his first hallucination when he envisions the dagger at the beginning of Act 2.  At this point in the play, he is still considering whether or not he should follow the plan that he has made with Lady Macbeth to murder King Duncan.  Macbeth acknowledges that Duncan is a good king and that he is loved by all in Scotland; however, his desire for power challenges his sense of loyalty to Duncan and Scotland.  Macbeth thinks that the dagger calls him towards committing the murder, so he decides to go through with the plan.  Later, Macbeth has Banquo murdered to protect his place on the throne, but Macbeth also realizes that Banquo is a good man.  He hallucinates Banquo's ghost after he falsely honors Banquo in front of the guests at the banquet.  So, Macbeth's hallucinations show that Macbeth is grappling with the decisions that he has made while trying to go after his ambition.

Macbeth's visions and hallucinations play a pivotal role in his ambition for power and in his development as a character.

From Act I, Scene 3, in which Macbeth encounters the three witches, the "vaulting ambition" of Macbeth takes him into the phantasmagoric realm of visions and things imagined. These visions and hallucinations of Macbeth then become the objective correlatives of both his fears and his guilt.

Prior to his murder of King Duncan, for instance, in his troubled mind Macbeth knows that Duncan, who is his kinsman, is a virtuous man, having "borne his faculties so meek" (1.7.17). And because of his fears and twinges of conscience, Macbeth envisions a dagger before he commits his dastardly act of regicide. This dagger is the objective correlative of the emotions that Macbeth feels as he is about to commit the terrible crime:

Art thou but
A dagger of the mind, a false creation,
Proceeding from the heat-oppressed brain? (1.7.36-39)

Similarly, Macbeth's guilt tortures him as, after Banquo's murder, he envisions the ghost of this noble man. In Act III, Scene 4, in his guilt Macbeth feels confronted by the ghost of Banquo, and with trepidation he speaks to this ghost:

Thou canst not say I did it: never shake
Thy gory locks at me. (3.4.54-55)

After the ghost of Banquo reappears, Macbeth's paranoia grows as "nothing is but what is not" and he begins to lose his hold upon what is real and what is not. In this fear Macbeth tries to eliminate anyone who may be a threat to him. He revisits the witches for assurance that he will remain king. When he demands to know about the future, the witches summon apparitions to inform him. The first apparition is that of an armed head that tells him to be wary of Macduff; the second is a child, covered with blood, that states that no man born of a woman will cause harm to Macbeth; and the third vision is that of a child wearing a crown who is holding a tree. This apparition says,

Macbeth shall never vanquished be until

Great Birnam Wood to high Dunsinane Hill

Shall come against him. (4.1.96-98)

Macbeth sees visions and hallucinations as a sign of his guilty conscience for murdering King Duncan. When Macbeth is about kill King Duncan, he sees a bloody dagger floating in the air. The dagger which is covered in blood is pointing toward the king's chamber.

Again, Macbeth sees hallucinations in the form of Banquo's ghost. Banquo is seated in Macbeth's seat of honor. Having had Banquo murdered, King Macbeth is dealing with his guilt. In a sense, Macbeth is losing his mind. He is suffering from the guilt of having his friend Banquo murdered.