What is some textual evidence about Macbeth's downfall in Macbeth?
According to renowned Shakespearean critic Harold Bloom, Macbeth is a tragedy of the imagination. Thus, Macbeth's downfall results from the horror and the hallucinations generated by his imagination.
From the beginning, Macbeth seems susceptible to his imagination that impels him toward the destruction of his better nature. First of all, despite Banquo's adjurations, Macbeth's imagination finds the predictions of the menacing "weird sisters" enticing, if not credible. Yet, while he is seduced by their predictions of his being king, he is also frightened as the nature of the witches seems menacing. Reality and fantasy, then, become equated in Macbeth's mind: "nothing is/but what is not."
In Act I, urged by Lady Macbeth to act upon the witches' predictions, Macbeth deliberates upon the act of regicide that his wife wishes him to commit. He can find no reason to murder this virtuous king, his lord and kinsman, other than his "vaulting ambition" that spurs him on. Therefore, he tells Lady Macbeth "We will proceed no further in this business" (1.7.33), but she attacks his manhood and Macbeth is spurred on to action. Yet, before he kills Duncan, Macbeth imagines a bloody dagger, "a dagger of the mind" (2.2.37), and he presages his future confusion between what is and "what is not."
Macbeth's imagination continues to dominate him so much that no sooner does he contemplate an ambition than he perceives himself having already committed the act that fulfills this ambition. Thus, he moves from one bloody act to another. And, the more bloody the acts that Macbeth commits, the more horrific his imagination becomes. In Act III, for instance, he speaks of "the affliction of these terrible dreams/That shake us nightly...(3.2.18-19). Indeed, Macbeth's imagination itself becomes bloody as blood is the main constituent in his mind. He believes that the blood he has already shed (i.e. Banquo's) will return for revenge against him: "It will have blood, they say: blood will have blood" (3.4.128).
Macbeth's doppelgänger, Lady Macbeth, suffers the same fate of hallucinations, sleeplessness, and paranoia. Nightmare haunts them both. In Act III, for instance, Macbeth plans the death of Banquo and Fleance, anxious about the predictions of the witches that Banquo will have sons who will become kings:
We have scorched the snake, not killed it.She’ll close and be herself whilst our poor maliceRemains in danger of her former tooth.But let the frame of things disjoint, both the worlds suffer,Ere we will eat our meal in fear, and sleepIn the affliction of these terrible dreamsThat shake us nightly. (3.2.15-23)
Bloom contends that the witches "...place nothing in Macbeth's mind that is not already there" although they certainly influence him into yielding to this vaulting imagination of ambition. Further, his imagination creates a phantasmagoric realm so complex and horrific that it destroys the Macbeths.
In the end, Macbeth imagines that Birnam Woods moves, thus fulfilling the witches' predictions of his demise, and Macbeth becomes desperate as his mind is filled with wild imaginings. Macbeth tells Macduff that he is safe--"charmed"-- because he cannot be killed by any man born of woman. But, when Macduff informs him that his mother died before he was born and he was cut out from her womb, Macbeth curses,
Accursed be that tongue that tells me so,
For it hath cowed my better part of me. (5.8.17-18)
Thus defeated by his imagination that is terrorized by Malcolm's prophetic words, Macbeth informs Macduff, "I'll not fight with thee" (5.7.22), though he quickly changes his mind and is soon slain.