Macbeth's moral downward spiral from loyal subject and brave soldier to serial killer might seem to be ordained by gods and witches and karma, but Macbeth allowed himself to commit all these acts - it was his choice to believe the prophecies of the witches in the beginning of the story, to allow himself to be manipulated by Lady Macbeth, to continue the killing spree to include innocents, and to seek out the witches again. He allowed his future to be molded by external forces, but it was his choice to do so.

Macbeth became Thane of Cawdor in the first Act by performing well in battle - killing Macdonwald. He chose to fight and to kill; he could have done any number of things to incapacitate his adversary, but he made the decision to "[unseam] him from the nave to the chaps" (Act I, Scene III, Line 24) . King Duncan appointed him Thane of Cawdor for that act, unwittingly setting a dangerous cause-and-effect in Macbeth's easily-influenced mine: Kill someone violently, be promoted to royalty.

Walking with Banquo in the third scene of Act 1, Macbeth encounters the "weird sisters", who greet him with his current and future titles. It's obvious Macbeth already had some unvoiced designs on the crown from his reaction, perhaps even of killing Duncan. Unlike Banquo, who questions the validity of the "fantastical" prophecy, Macbeth stands silently, making the mental leap from "All hail, Macbeth, thou shalt be king hereafter!" (Act I, Scene IV, Line 51) to "I'll have to brutally murder King Duncan". He asks where the witches got their "strange intelligence", vaguely questioning the meaning of their pronouncement, and asking them for clarification, but they vanish. Nine words from the witches, who give no explanation, or credentials, and Macbeth takes the prediction as truth - just the nudge he needed to act on his previous thoughts. When Ross and Angus meet Macbeth and Banquo, they make Macbeth sure that his choice to murder is the right one, by informing him that half of the witches' predictions for him were already true. The witches' first prediction is different in that it had not already been decided - Duncan appointed Macbeth Thane of Cawdor before Macbeth met the witches. Macbeth is the one who fulfills the witches other prophecy - he blames "chance" for the actions he will commit, saying "If chance will have me king, why, chance may crown me," (Act I, Scene IV, Line 147) but he doesn't just happen to stab Duncan by accident. Chance has no part in his crowning; he doesn't let it.

Chance is further circumvented by Lady Macbeth, who knows she can convince Macbeth to make decisions to satisfy her own ambitions - she says of her husband "[Macbeth] art not without ambition, but without the illness should attend it" (Act I, Scene V, Line 20) . She doesn't have to say much to convince Macbeth at first; they only exchange a few words on the subject. Macbeth could have made the choice to remain a model citizen, but his only reaction to the suggestion of murder is "We will speak further." (Act I, Scene V, Line 78) To his credit, and further illustrating that he acts on his own free will and not through supernatural mandate, Macbeth talks himself out of killing Duncan. Lady Macbeth steps in, and makes good on her promise to "chastise [him] with the valour of [her] tongue", imaginatively explaining why Macbeth must be king. Rather than argue with her, he agrees to her proposal to "wine and wassail" Duncan's guards, who will take the blame for the killing and be unable to testify against them, since they'll kill them, too.

The murderous rampage continues in Act 3, after Macbeth becomes king; he shows that he has made the choice to invalidate one of the witches' revelations and kill Banquo and Fleance by admitting to Lady Macbeth "full of scorpions is my mind, dear wife!" He chooses hit men, and sends them off to "set upon" Banquo and Fleance. Troubled by Fleance's escape, Macbeth seeks out the witches in Act 4, whom he trusts implicitly for some reason. They give him another set of seemingly contradictory prophecies - first to beware Macdff, but not to fear anyone born of a woman, and third that he'll be king until Birnam Wood moves. Macbeth listens only to the part he wants to hear; the the latter two. After the witches disappear, Lennox informs him that Macduff has organized a rebellion. Macbeth gives the order "seize upon Fife; give to the edge o' the sword His wife, his babes, and all unfortunate souls" (Act 4, Scene 1, Line 165), a death warrant for any innocents who stand in his way of fulfilling the witches' promise for his long-term reign as king. Unfortunately for him, it also convinces Macduff that Macbeth must die by his hand.

Macbeth chose to selectively believe what the witches told him, even though their predictions weren't all accurate - Macduff became Thane of Cawdor and later king, but Banquo's sons never did. Further, the first pronouncement was of something that had already been decided, not a future event. In the second witch scene, they predict the events of the play accurately, but only by technicalities - Birnam wood didn't really move; just some of its trees did, and Macduff was not "born" of woman in the usual sense, but he obviously did come from a woman. Macbeth allowed his wife to talk him into murder and cove up, but the decision to kill Banquo and Lady Macduff was his own - he didn't need a crystal ball or to be chided into it. He may have been a pawn of the witches and Lady Macbeth, but he never did anything he wouldn't have done on his own.