A lobby in the castle — "if it were done"

A lobby in the castle, during the banquet. Macbeth has slipped out alone. The soliloquy that follows is the play's most lucid argument against itself. "If it were done, when 'tis done, then 'twere well it were done quickly." The grammar is knotted because the thinking is. He moves through every reason not to do it. He is Duncan's kinsman, his subject, his host — bound three ways by duty. Duncan's virtues "will plead like angels, trumpet-tongued, against the deep damnation of his taking-off." The only spur is "vaulting ambition, which o'erleaps itself." He concludes: "we will proceed no further."

Lady Macbeth enters. He tells her his decision: the king has honoured him; he will not throw away the new golden opinions he has bought. She replies with one of the most sustained pieces of psychological assault in Shakespeare. Was the hope he dressed himself in drunk? Is he a coward? She delivers the line that has unsettled audiences for four hundred years: "I have given suck, and know how tender 'tis to love the babe that milks me; I would, while it was smiling in my face, have plucked my nipple from his boneless gums and dashed the brains out, had I so sworn as you have done to this."

He yields. He asks, almost weakly: "if we should fail?" She answers: "we fail? But screw your courage to the sticking place, and we'll not fail." Then the plan. She will give Duncan's grooms wine until "their drenched natures lie as in a death." She and Macbeth will do the deed with the grooms' own daggers and smear the grooms with the king's blood. Macbeth, mended, accepts. "I am settled, and bend up each corporal agent to this terrible feat. Away, and mock the time with fairest show: false face must hide what the false heart doth know."