Shakespeare’s handling of the three witches or “weird sisters” of Macbeth is in itself equivocal. He assigns them the first dozen lines of the play their proclamation that “fair is foul, and foul is fair” (I, i., .11) setting the tone for the horrid events ahead. When their prediction of Act I, scene iii that Macbeth will become Thane of Cawdor comes true almost instantaneously, the broad contours of the play’s plot are set; Macbeth will become king of Scotland and this will require the elimination of Duncan and his sons. While the witches perform seminal and salient functions in the play, their appearance on stage is nonetheless limited. Assuming that Act III, scene v. of Macbeth as we have it was written into the play after the Bard’s death, Shakespeare gives us only one more glimpse of the weird sisters in Act IV, scene i. with its famous “double, double, toil and trouble” (l,10) invocation of evil. We see very little of the witches and this, in turn, contributes to our uncertainty about who or what they are. They clearly possess supernatural powers, including the capacity to foretell the future and to read the minds of the mortals with whom they come in contact, and this suggests that they are real but supernatural. On the other hand, even after their final manifestation at the start of Act IV, Shakespeare undercuts the reality of the witches, again raising the possibility that the weird sisters are an hallucination, an emanation from the human psyche.

The key characteristic of Macbeth’s witches is that while they can influence Macbeth’s actions, they cannot compel him to commit the evil deeds that he undertakes in the course of the Scottish tragedy. This limitation on the power of the weird sisters, their dependency upon human will to work their black arts, is highlighted by the difference between Banquo’s reaction to their initial predictions and that of Macbeth. After their encounter with the witches in Act I, scene iii, Banquo wonders aloud about whether they were real or whether he and Macbeth are suffering from some type of hallucination: “Were such things here as we do speak about?/Or have we eaten on the insane root/That takes the reason prisoner?” (I, iii., ll.83-85). It is not Macbeth, but Banquo, who first notices the witches on the heath, asking Macbeth: “What are these/So withered and so wild in their attire/That look not like th’ inhabitants of the earth/And yet are on’t” (I, iii, ll.39-42). Banquo then asks the witches directly whether they “live or are “aught” and Macbeth demands further, “Speak, if you can, what are you?” (I, iii., l.47). They do not respond to these questions, but simply hail Macbeth, first as Thane of Glamis, then as Thane of Cawdor, and finally as “King hereafter.” When Banquo asks that witches if they can foretell future, they hail him as a future sire of Scottish monarchs, and when Macbeth then asks the witches to explain their salutations and the means by which foresee future, they vanish into thin air. Banquo ultimately concludes that the witches are not an hallucination, nor are they of substance, explaining to Macbeth that, “the earth hath bubbles, as the water has/And these are of them” (I, iii, ll.79-80).

Since both Macbeth and Banquo actually see the witches, and since both are of sound mind before and immediately after this encounter, the alternative thesis that the witches are only mental figments seems false. Moreover, Lady Macbeth (while she is in her right mind) accepts the reality of the witches having an independent existence. Nevertheless, Shakespeare deliberately upsets any firm conclusions as to who or what the weird sisters are. When Lennox arrives in Act IV, scene i, after the witches have vanished into air, Macbeth asks whether he saw them. Lennox replies with a simply no, and while his failure to see them is most plausibly the result of his having entered the scene too late, we are again thrown off balance.

Leaving the issue of the witches’ nature aside for the moment, we find that while the weird sisters can influence humans like Macbeth to carry out heinous acts, they cannot force them to do so, nor do they intervene directly in the commission of crimes. In facing the weird sisters, Macbeth undergoes a two-stage process: he first determines that they are credible and then decides to act upon this assumption. The first step occurs when word comes through Rosse and Angus that King Duncan has directed them to call Macbeth by his new title of Thane of Cawdor. Both Macbeth and Banquo then lend credence to the witches’ ability to see into the future. Banquo, however, refuses the temptation of taking the second step, saying that, “The instruments of darkness tell us truths,/Win us with honest trifles, to betray ‘s/In deepest consequence” (I, iii., ll.124-126). Macbeth, however, furnishes the witches with the essential ingredient for the mayhem they are brewing, the agency of his will. He first assumes a neutral stance toward acting upon the prediction that he will become king, asserting that “This supernatural soliciting/Cannot be ill, cannot be good” (I, iii., ll.130-131). Macbeth presumes that even though his encounter with the witches incites terror in him, it cannot be “ill” because it augured his success in becoming Thane of Cawdor. At this juncture, Macbeth has headed down a slippery slope: once he proceeds with “weighing” the value of the witches’ predictions he is only a short distance from subordinating his own will into an instrumentality of evil.

The contrast between Banquo and Macbeth in relation to the witches surfaces again at the start of Act II when Banquo confides to Macbeth that he has dreamt of the three weird sisters, while Macbeth replies that “I think not of them” (l.22). This is, of course, a lie and a denial of reality, for right after this exchange and once Banquo leaves, Macbeth sees a dagger hovering before his eyes, and places it in the specific context of his meeting with the witches: “Now o’er the one half world/Nature seems dead, and wicked dreams abuse/The curtain’d sleep; witchcraft celebrates/Pale Hecat’s offerings” (II, i., ll.49-51). It is important to note that in his second (and final) encounter with the witches (Act IV, scene i.), Macbeth takes an active hand in conjuring the apparitions that furnish him with an equivocal security about his future as Scotland’s king. In the course of the play, the witches paradoxically become less real, but more potent. In the end, the reality of the witches is predicated upon the willingness of human beings to perform their evil handiwork and in the character of Macbeth, this willingness is plainly present.