This is the driving force behind Macbeth's evil actions. His ambition to be king, encouraged by his wife, leads to the murder of Duncan.
The witches' declaration that 'foul is fair' runs through the play in physical and internal conflicts, and in the motifs of day and night.
A dagger appears to Macbeth before he kills Duncan, and Lady Macbeth sees spots of blood on her hands.
The witches set the scene for the play, foreshadowing the foul-play that follows. Macbeth seeks them out again and they prophesy his death.
A series of 'revenges' run through the play, following on from the murder of Duncan. Macduff's vengeance ends the play when he kills Macbeth.