Example:

"Anon.
Fair is foul, and foul is fair:
Hover through the fog and filthy air."
(Act 1, Scene 1, Lines 10-12).


Explanation:

This statement contradicts itself. A simpler way to put this phrase would be "you can't judge a book by it's cover." Things that seem foul may be fair, and vice versa. It appears firstly to the weather: which, though foul, the three weird sisters naturally find it fair. Then it too sums up that foul things are desirable, and fair things are not. It also looks forward to the action of the play; for Macbeth and his wife will seem fair at first, though in fact inwardly foul.