This is a central question to Macbeth. Certainly, Shakespeare deliberately introduces an element of the supernatural into the play with the witches, whose prophecies for the future set the plot into motion. Their prediction that Macbeth will be Thane of Cawdor and "King thereafter" piques his ambition, and sets him on the murderous path that ends with his death. Later, their prediction that Macbeth could only be killed by one "not of woman born" embolden him, though eventually he discovers that this prophecy is referring to Macduff, born by a caesarian procedure. Yet it is not clear whether the witches are simply describing a future that is fated to occur, or whether Macbeth's own actions make it happen. Similarly, many have wondered whether Macbeth would have committed the crimes without the influence of his wife. Whether or not these events were preordained, or if they could have been avoided, it is clear that Macbeth's ambition drives him to commit horrible crimes, with the malevolent influence of the supernatural always pushing him along.