Fair is foul, and foul is fair: / Hover through the fog and filthy air.
Act I, Scene 1 · The Three Witches
Context
All three witches chant this phrase in unison as they prepare to depart from the heath, concluding the play's opening scene.
Analysis
The chiasmus inverts the terms 'fair' and 'foul' to create a syntactic mirror that denies any fixed meaning to either word. Shakespeare reinforces this confusion through the hissing alliteration of 'f' sounds in 'fair,' 'foul,' 'fog,' and 'filthy,' which sonically blurs the boundary between opposites and makes the entire line feel slippery and indistinct. By having all three witches speak together, the play presents this moral reversal not as one character's opinion but as a cosmic principle.
Essay Tip
Use this to argue that Shakespeare establishes appearance versus reality as a structural problem in the play's first minutes—the witches' chant doesn't describe a world where things look different than they are, but rather one where 'fair' and 'foul' have become the same thing, so no stable judgment is possible.