Answer:
With a clap of thunder, the Witches reappear. Having demonstrated their power by casting a terrible curse upon a sailor whose wife offended one of them, they encounter Macbeth and Banquo as the two soldiers ride from the battlefield. The sisters make three prophecies, the first two regarding Macbeth and the last regarding Banquo. Macbeth shall be named as Thane of Cawdor and then king; Banquo, although he shall not himself rule in Scotland, will be father to future generations of kings. Immediately, the Witches vanish into thin air, leaving the two captains in amazement. Ross and Angus arrive on the scene to confirm what we already know, that Macbeth is to be invested with the thaneship of Cawdor. The Witches' first prophecy has come true.
Step-by-step explanation:
Ross arrives and announces that Macbeth is to be the new Thane of Cawdor, thus confirming the first prophecy of the Witches. Banquo and Macbeth are struck dumb for the second time, but now Shakespeare contrasts their responses. Banquo is aware of the possibility that the prophecies may have been the work of supernatural dark forces, as exemplified in his lines "What? Can the Devil speak true?" (108) and "oftentimes, to win us to our harm, / The instruments of Darkness tell us truths . . . — (only) to betray us" (123-125). Macbeth is more ambiguous. His speech is full of what will now become his trademark — questioning, doubting, weighing up, and seeking to justify: "This supernatural soliciting / Cannot be ill; cannot be good" (130-131).
Nevertheless, however much he reasons, Macbeth cannot reconcile the fact of the truth of the first prophecy with his intense and unnatural fear, or what he calls his "horrible imaginings." He admits to being so shaken by the news that he feels that his reason has been taken over by his imagination. The line "Nothing is, but what is not" is ambiguous. The expression could indicate confusion between the world we think of as real and the world of dreams, a neat summary of a confused mind. But how confused is Macbeth at this point? If he is capable of arguing that the prophecies are neither evil nor good, he is capable of accepting that nothing that exists has any existence or meaning. This interpretation could open Macbeth to dangerous and unjustifiable deeds. If he can make himself believe that "Nothing is, but what is not," then Macbeth's respect for order, for hierarchy, for the King, is also nullified. He can, literally, get away with murder.