What do the witches represent thematically in Shakespeare's Macbeth?
In the first scene of the play, when the Weird Sisters discuss their plan to meet with and deceive Macbeth, they initiate one of the play's most important motifs. Together, they chant, "Fair is foul and foul is fair / Hover through the fog and filthy air" (1.1.12-13). We see this motif resurface many times throughout the play, such as when Lady Macbeth tells her husband to look like a flower but be the serpent under it, or when Duncan admires the look of the Macbeths' home not realizing that he will be killed there that night. This motif leads to the theme that appearances can be deceiving.
Also, we know the Weird Sisters to be vindictive and malicious (especially from the one witch's dealings with the woman who would not share her nuts), and they as much as admit to the fact that they seek to deliberately manipulate Macbeth with the statement quoted above. Such manipulation is only possible when Macbeth is free to make his own choices and is not the pawn of fate, as some might have it. Therefore, the Weird Sisters also help to illuminate the theme that we are responsible for the choices we make because they are not governed by fate.
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