Do the witches *make* Macbeth evil? They don't have that kind of power. They can already work with what is already there. Having said that, they do seem to have awaken something within him. They plant the seeds that he allows to grow into pure evil.
Had they not told him anything about his future, he may have gone along happily fighting on Duncan's sides and, just as happily, being rewarded for his acts. The witches are masters at sowing seeds that humans use to destroy themselves.
Macbeth knows that what the witches tell him "cannot be ill", but also "cannot be good." Unlike Banquo , who immediately suspects the witches motive (he says sometimes the instruments of darkness tell small truths to gain the soul), Macbeth seems willing to suspend his misgivings, even to the point where he almost immediately pictures himself...
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