This supernatural soliciting / Cannot be ill; cannot be good. If ill, / Why hath it given me earnest of success, / Commencing in a truth? I am Thane of Cawdor: / If good, why do I yield to that suggestion / Whose horrid image doth unfix my hair, / And make my seated heart knock at my ribs, / Against the use of nature?
Act I, Scene 3 · Macbeth
Context
Macbeth, alone in thought after being named Thane of Cawdor, struggles to determine whether the witches' prophecy is good or evil, noting that while it has brought him success, it also fills him with a horrifying vision that makes his body react with terror.
Analysis
The repetition of "Cannot be ill; cannot be good" traps Macbeth in rhetorical paralysis, with each half of the sentence canceling the other out, mirroring his inability to reach moral clarity. The physical imagery—hair standing up, heart pounding—grounds the moral crisis in bodily involuntary reactions, showing his conscience knows something his mind is still debating. The phrase "against the use of nature" is crucial: his body is rebelling against what he's thinking, registering it as unnatural even as his ambition pulls him forward.
Essay Tip
Use this to argue that Macbeth's tragedy is partly a failure of self-knowledge—his body tells him plainly that his ambition is unnatural and wrong, but he treats his physical horror as a puzzle to be solved rather than a warning to be heeded, showing reason in service of desire rather than truth.