What are the reasons Macbeth would kill King Duncan, and what are some reasons not to?
After receiving the prophecy from the Three Witches in Act 1, Scene 3, Macbeth immediately begins thinking about assassinating King Duncan once he learns that he has been named Thane of Cawdor. Macbeth's foremost motivation for killing Duncan is to become king of Scotland. Macbeth craves the authority and absolute power a king possesses, which motivates him to commit regicide. Macbeth is also motivated to fulfill his prophecy, enhance his social status, please his wife, and leave an impressive legacy.
Despite the numerous reasons that support Macbeth's desire to kill King Duncan, there are also many opposing reasons for Macbeth to not follow through with the murder. If Macbeth commits regicide, he will more than likely live a life full of guilt, grief, and regret, given the fact that Duncan is his cousin and murder is against natural law. The social order of Scotland would also be upset, and chaos would likely result from Macbeth's unjust reign. Furthermore, the Three Witches' prophecies might not be correct; they could lead Macbeth down a dangerous path. Macbeth would still be forced to kill Malcolm, and Duncan's assassination would only lead to further bloodshed. Macbeth's soul would also be doomed if he were to kill the king, and Macbeth would only create more enemies.
Some reasons MacBeth would want to commit regicide and kill King Duncan:
1. To gain power over all of Scotland and advance his station in life.
2. To achieve the crown.
3. To fulfill the prophecy.
4. To look like a "man" in his wife's eyes.
Some reasons NOT to kill Duncan include
1. Murder is against natural law.
2. Killing a King will disrupt the Elizabethan cosmology and chaos would soon result.
3. Disorder, chaos, and unnatural acts will be loosed on the world.
4. The Weird sisters may not be a reliable source of information or prophecy. Why should he trust them?
5. Guilt and a stained conscience will inevitably result in psychological ailments.
Yes, Macbeth has the prophecies. He seems to think that he should be king because he has been told that he is. He was basically told three things: He was Thane of Glamis, he would be Thane of Cawdor, and he would be king. Since the first was true and the second came true, he figures the third should be too.
Correction: Perhaps I might have been clearer if I had written "Shakespearean Cosmology" in my post #2 above. What I meant by the Shakespearean Cosmology is his belief and use of the great chain of being. Check out