is this a dagger which i see before me

The phrase "is this a dagger which I see before me?" is taken from William Shakespeare's play Macbeth. It is spoken by the main character, Macbeth, during a soliloquy in Act II, Scene 1. In this scene, Macbeth is contemplating whether to proceed with the plan to kill King Duncan. As he waits for the time to strike, he imagines seeing a dagger in front of him. The phrase questions the reality of the dagger and signifies Macbeth's mental state, foreshadowing his descent into madness and his willingness to commit the morally wrong act of regicide.