If you’re discussing Shakespeare’s infamous “Scottish play,” and ask why Macbeth killed King Duncan, most people will say that he was an ambitious, scheming bastard, with an ambitious scheming wife. Both those things are true, but if you look at the text closely there’s something interesting going on.
But first, a little history. Shakespeare stole the story of Macbeth from Raphael Holinshed’s Chronicles of England, Scotland, and Ireland, a history book published in the late 16th century. Now, the standards of history back then were a little looser than ours, but if fact, Macbeth and Duncan were historical people, both kings of Scotland. Duncan, aka Donnchadh mac Crìonain, reigned from 1034-1040, and MacBheatha mac Fhionnlaigh, followed directly after, reigning from 1040-1057.
The Chronicles has all the familiar elements, complete with witches, an ambitious queen, the murder of King Duncan, a moving forest, and Macbeth’s subsequent death at the hands of Makduff “who was neuer borne of my mother, but ripped out of her wombe”. Ambition is clearly the motive in the original story; when the witches first foretell Macbeth’s kingship, Duncan has no heirs and Macbeth assumes he will succeed the king once Duncan dies. However, Duncan subsequently marries and has two children, which quash Macbeth’s hopes for the throne, prompting him to plot the king’s death.
Shakespeare, however, has compressed the tale, and Duncan already has two sons. In fact, he appoints one of them his successor in Act 1, scene 4. That would appear to maintain a parallel motive. However, in Act 1, scene 3, immediately after the witches vanish and Macbeth is informed he is to be Thane of Cawdor, he says, “why do I yield to that suggestion whose horrid image doth unfix my hair and make my seated heart knock at my ribs … My thought, whose murder yet is but fantastical, shakes so my single state”.
Macbeth is plotting murder already – even before he knows Duncan has another heir in mind. The same is true of Lady Macbeth, who, upon getting her husband’s letter, says, “Make thick my blood; stop up the access and passage to remorse, that no compunctious visitings of nature shake my fell purpose”.
Now the simplest theory, and perhaps the one Occam’s Razor would suggest, is that Shakespeare simply got ahead of himself, and slipped in the mention of murder early. However, that’s no fun for grad students who are supposed to be going over the text with a fine-toothed comb. So naturally, I have an alternative theory, which is that Shakespeare was channeling Flip Wilson 400 years early and “The devil made him do it.”
This is not as far-fetched as it may sound. We know that Macbeth was written soon after King James ascended the throne of England, and that Shakespeare’s acting company, formerly the Lord Chamberlain’s Men, was now under the patronage of James himself, and was now The King’s Men. Clearly, with a new king and patron, Shakespeare needs to impress the king.
It’s well known James had a real fear of a) witches, and b) being murdered. He wrote a book on witchcraft called Daeomonologie, and had attended a witch trial in Scotland. There had been at least two attempts on his life, the Gowrie Conspiracy and the Gunpowder Plot, and that witch trial in Scotland was brought on the belief that witches had affected the weather and tried to cause him to be shipwrecked when he returned from Denmark with his new bride.
So, what does Shakespeare do? He whips up a supernatural thriller, The Exorcist of 1605, where witches corrupt Macbeth to kill the legal king of Scotland. Not only that, but he brings in one of the kings own relatives in a ghostly cameo. Banquo was the father of Fleance, who according to Holinshed, was the founder of the Stuart line from whom James descended. (Sucking up to James is why Shakespeare changes history in the play. According to Holinshed, Banquo was involved in the plot against Duncan. But it wouldn’t do to call the king’s great-great-…-grandfather a regicide, so Banquo is innocent in Shakespeare’s version.)
There are some other details to support this view as well, but I’m saving them for my research paper.