Although the Three Witches and Lady Macbeth play a significant role in influencing Macbeth to assassinate King Duncan, it is ultimately Macbeth's decision to follow through with the bloody murder, which is why he is primarily responsible for the king's death.
Macbeth is the play's tragic hero, whose inherent character flaw is his "vaulting ambition." Immediately after receiving the favorable prophecies from the Witches, Macbeth begins thinking about murdering King Duncan and acknowledges his bloody thoughts by saying:
If good, why do I yield to that suggestion Whose horrid image doth unfix my hair And make my seated heart knock at my ribs,
Against the use of nature? Present fears Are less than horrible imaginings (1.3.138–141)
After informing his wife about the Witches' prophecies and his new title as Thane of Cawdor, Lady Macbeth encourages Macbeth to follow his heart and assassinate the king. Despite his initial reservations, Macbeth recognizes that his ambition is the only thing motivating...
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