According to Shakespearean scholar, A.C. Bradley, "while the influence of the witches' prophecies on Macbeth is very great, it is quite clearly shown to be an influence and nothing more. There is no sign in the play whatever that Shakespeare meant the actions of Macbeth to be forced on him by external powers." Bradley's argument is valid; the witches provide the spur Macbeth needs to act on his overbearing ambition, but it is ultimately the choice of Macbeth and Macbeth alone to pursue his thirst for the throne - to turn his thoughts into actions. The influence of the witches is indeed no more than an influence, as is demonstrated by Macbeth's initial reaction to their prophecies, his subsequent independent decisions to murder for the kingship, and his own admittance in the end that his actions were of his own doing and not forced on him by external powers.
Macbeth's immediate reaction to the witches' prophecies is the first clear piece of evidence that Shakespeare did not intend for them to be anything more than an influence. Upon first hearing their prophecy that he will be king, Macbeth's response is telling: he starts. This reaction suggests that before Macbeth even stumbles upon the presence of the Weird Sisters, he has thoughts of becoming king. Moreover, the suggestion is not simply that he has considered it - for starting is a sign of guilt, of which he would have little if his thoughts were innocent - but that he has considered acting on it - a crucial distinction. The prophecy itself contains little but the mention that he will be king: "All hail, Macbeth! that shalt be king hereafter!" (I, iii, l. 50)1 Indeed, Bradley observes that the witches "merely announced events: they hailed him as Thane of Glamis,