It is not only the witches that help to convince Macbeth to kill Duncan - his wife also plays an important role. As soon as Macbeth lets her know of the prophecy in a letter, she "[fears his] nature [is] too full o' the milk of human kindness to catch the nearest way" (that being the murder of Duncan), and so she sets about trying to convince him to do it. She challenges his manhood, telling him that "When [he] durst do it, then [he was] a man;
And, to be more than what [he was], [he would]
Be so much more then man. Nor time nor place
Did then adhere, and yet [he] would make both:
They have made themselves, and that their fitness
Does unmake [him].",
with "unmake" meaning "castrate", thus removing his masculinity. Together, the influence of the witches and Lady Macbeth convince him to murder Duncan.
Of course, the killing of Duncan is not the only factor in Macbeth's downfall - he also kills Banquo, attempts to kill Fleance, and orders the murder of Macduff's wife, children and servants.
The killing of Banquo is forgivable under these unusual circumstances - Macbeth realises that he has made a mistake in killing Duncan, but "What's done cannot be undone", as Lady Macbeth says in a later scene - he now has to deal with the consequences, one of them being that Banquo becomes suspicious of him. There is no way that Macbeth can quell Banquo's suspicions, and so to retain his rank Macbeth sees no other option than to kill him. Once again, although this step of Macbeth's downfall is taken by the man himself, under the circumstances blame cannot be put upon him - he has lost his perspective; murder seems to be the only way for him to continue his life.
On the other hand, the killing of Fleance is less forgivable. In their prophecy, the witches tell Banquo that "[he] shalt get kings", meaning "[his] children shall be kings" as Macbeth later clarifies. So Macbeth knows, insofar as he believes the witches, that to remain king and have his descendants be kings, Fleance must be killed. This is a killing in the name of ambition rather then self-protection, as is the murder of Banquo, and so the question of whether the prophecy informs or inspires Macbeth must once more be addressed. As already stated, Macbeth would have believed the witches due to the cultural nature of the times, and the veracity of their statement would seem to have been proven by Macbeth becoming Thane of Cawdor, and so it is understandable that Macbeth would have believed that Fleance would grow up to overthrow him. Macbeth's plan to murder him to prevent his doing this is indicative of his degenerating sense of perspective, as mentioned above.
By the time Macbeth orders the murder of Macduff's household, it is arguable that Macbeth's downfall has already come. Four people have died either by his hand or by his order - Duncan, two guards and Banquo - and the more people he kills the worse it will be if he is exposed, and he sees the only way of preventing that is to kill more people - a logic that could perhaps be considered twisted. I once again repeat that it is only partially his fault that he actually arrives in this predicament in the first place.
As with many of Shakespeare’s works, dialogue is not the only constituent of Macbeth – the soliloquies of the main character reveal much of their character and their thoughts. In act one, scene 7, Macbeth himself tells us that he has
“no spur
To prick the sides of [his] intent, but only
Vaulting ambition, which o’er-leaps itself
And falls on the other.”
Macbeth is telling us that his only diving force is ambition, and h realises that this ambition will “o’er-[leap] itself”, and bring him ill. The whole soliloquy in this scene tells of Macbeth’s doubts about the murder of Duncan, how “[Duncan’s] virtues will plead like angels…against…his taking-off”, meaning his murder, and how the fact that Macbeth’s position as Duncan’s “kinsman and... subject [are] both strong against the deed” – he is a loyal friend and subject to Duncan and these two factors are strong reasons for him to not kill him. The soliloquy shows that Macbeth is fighting against what he sees as his destiny: he feels that he has to kill Duncan although he can see myriad reasons not to.
Although claiming that Maccbeth is insane is a weak defence, he himself refers to himself as that in Act 2, scene 1, when he “sees” the dagger he is to murder Duncan with, and questions whether it is “a false creation, proceeding from the heat-oppressed brain”.
Having defended Macbeth on account of his suggestibility and the circumstances in which he would have lived, his behaviour, although understandable, is not entirely excusable. A certain amount of free will definitely plays a part in his downfall; looking back to when he first meets the witches, murder immediately comes to his mind when they tell him he will be king. It is obvious that Macbeth concludes that murder is the answer under his own steam – most people would wonder how such a thing could occur rather than starting to plot illegal and highly immoral activities. Macbeth’s murdering Duncan is certainly very strongly influenced by Lady Macbeth, and although we know that Macbeth is a man of weak constitution, if we look at his actions in a harsher light it was still his decision to commit murder, both relating to Duncan and other characters later in the play.
I conclude by saying that I believe was responsible for his downfall only in the sense that he committed acts that led to it - he cannot be held accountable for his actions. Macbeth is a character susceptible to suggestion by people he perceives as stronger than him – for example Lady Macbeth and the witches - who have either natural or supernatural power over him.
