My thought, whose murder yet is but fantastical, / Shakes so my single state of man / That function is smother’d in surmise, / And nothing is but what is not.
Act I, Scene 3 · Macbeth
Context
Macbeth, still in aside, admits that the mere thought of murder—though still only imaginary—overwhelms his ability to function and distorts his sense of reality.
Analysis
The phrase "nothing is but what is not" uses a stripped-down, almost primitive syntax (monosyllables, repetition of "is") that enacts cognitive collapse—language itself is breaking down under the weight of Macbeth's fantasy. He describes a state where imagination has overpowered reality so completely that the actual present ceases to exist and only the imagined future feels real. The word "fantastical" still acknowledges the murder is imaginary, yet it has already "smothered" his ability to act in the real world, showing thought has become more powerful than fact.
Essay Tip
Support a thesis that Macbeth's internal collapse precedes and causes his external crimes—this line shows that his grip on reality breaks the moment he entertains the idea of murder, meaning the psychological damage happens before any action, making the later violence almost an afterthought.