Discuss the advantages and the disadvantages of the use of Witches in "Macbeth".

Why Shakespeare uses a supernatural element like the witches in "Macbeth"?
The answer is quite simply: Shakespeare uses the element of unknow to evoke fear in the minds of his audience and since the Witches were symbol of evil also the fear of the devil – paople used to feel in the period – gives an additional intriguing effect of haunting.

In Shakespeare's time, witches were believed to have supernatural powers: they could transform themselves into other shapes. In "Macbeth" dark powers are now represented – and so they are transformed – in witches: in fact the Weird Sisters symbolizes the capacity to influence men's decision, but more importantly they are an outward representation of the darkness in Macbeth's heart and the evil nature of his orrible deeds.

But consider now the language that Shakespeare uses: as the play begins, we are introduced to the witches. They speak in rhyming couplets, just as all supernatural elements in Shakespeare’s work do. This could have been to let the audience, which would have been aware of this technique (it recalls the ancient times and the orally texts), that the witches are in fact magical. It also helps the reader to remember the speech.

Furthermore the supernatural element was a current and typical feature in Shakespere's time, not because during the Renaissance people believed in witches, but because the element of "Witch" recalls Medioeval traditions: since Shakespeare used the witch as a negative element the text is accepted by the traditional religious and cultural codes.
This means Shakespeare wanted to analyze the medieval world in a Reinaissance prospect.

In my opinion using the "Wtich" to represent an inner and psychological element, is an hazard: not everybody are able to understand clearly the allusion and the meaning. But on the contrary, it conveys the idea of a fantastic plot with fantastic settings and characters, making "Macbeth" structured as a simple story you can read even to the children, and so even the lower class was able to deal and recognize the negative part witches had in the story.

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