In Shakespeare's play, Macbeth, Macbeth's sanity gradually diminishes. As he commits the murder of King Duncan, orders the killing of Banquo and Macduff's family, Macbeth's state of mind gets worse.
Before planning King Duncan's murder Macbeth's state of mind was both superior and sane. As he tries to go through to commit the murder, he realizes that what he is doing is wrong. He states "To plague th' inventor: This even-handed justice Commends the ingredients of our poisoned chalice to our own lips. He's here in double trust: First, as I am his kinsman and his subject, Strong both against the deed then, as his host, Who should against his murderer shut the door, Not bear the knife myself."" (Shakespeare 1.7.10-16). Showing his mental reasoning, with this statement there is no way he could be crazy. Trying to convince himself that this murder is, in fact, an insane thing to do. After King Duncan's murder, Macbeth becomes fearful and worried about his evil doing. When he says, "How is't with me, when every noise appalls me?- (Shakespeare 2.2.57) Macbeth is actually hearing the noise of Macduff and Lennox knocking on the door trying to wake the Porter. But to Macbeth it seems to him that he is hearing things. The interpretation of this quote from the play can be that, "what Macbeth hears is not Macduff and Lennox trying to awaken the Porter, but all the powers of hell and heaven knocking simultaneously at his heart- (Goddard 120). Even though he heaven and hell are knocking at his heart, he still committed the murder of Duncan; therefore, "he is at the gate of hell indeed, but still outside- (Goddard 120). Because of the guilt he expresses, however, when he says "To know my deed, twere best not know myself./Wake Duncan with thy knocking! I would thou couldst!- (Shakespeare 2.2.72-73). This shows that Macbeth is sorry for what he has done and regrets killing Duncan. His state of mind now, is no longer sane.