One of the most memorable aspects of Shakespeare's Macbeth is the presentation and use of the three witches. They are typically Gothic, they develop the plot and the ambiguity surrounding them means you can talk about them in an exam without being limited to one or two interpretations.
The Witches - Context
Contextually, there's a lot to say about the witches. The play was written shortly after James VI of Scotland's succession to the throne, making him King James I. James was particularly interested in witches and believed in them so vehemently he decided to write a whole book on witches in 1597.
The book, Daemonologie, highlighted his insistence that witches existed and wielded supernatural powers. He took influence from the Bible, and he once blamed stormy seas on witches, because they were pretty much the perfect scapegoat for anything.
Shakespeare's witches are similar to the witches James spoke of so often. This, combined with the fact that James I was a big fan of Shakespeare's stuff, suggests that a huge source of inspiration for the characters was King James I himself.
So in an essay, you can use this contextual knowledge to form an interpretation that is contrary to your point; if an exam asks whether the witches are manifestations of Macbeth's guilt/products of his imagination/etc., you can provide the interpretation that the witches may just be included to appease King James I.
It's interesting to note that the play opens with the witches, and you can talk about this in terms of the play's structure. Do the witches frame the play, like Walton frames Frankenstein. By 'framing' the play in such a way, are we to expect that they have control over the events of the play and what happens?
The first scene is very short, but establishes one of the most important quotes in the play
"Fair is foul, and foul is fair;" This line is echoed by Macbeth - and it's actually his first line in the whole play: "So foul and fair a day I have not seen." The echoed line may indeed suggest that the witches are in control of Macbeth - and if they control him, how can he be to blame? If an exam asks whether Macbeth cannot by sympathised with/is a cold-hearted villain/etc. then you can argue that he is none of these things because he has no freedom over his actions. You could also argue that the echoing of this line enforces the interpretation that the witches are figments of Macbeth's imagination or are manifestations of his inner conflict. Alternatively, you could argue that the link between Macbeth and the witches blurs a line between "worthy Macbeth" and the 'evil' witches - perhaps suggesting that there is a darker side to the character who has been set up as a valiant hero. Later on the witches learn of Macbeth's imminent arrival and say: "something wicked this way comes" Macbeth is called "wicked" by the witches is…