What are three ways the Three Witches deceive people in the play Macbeth?
In Act 1, scene 1, the Weird Sisters discuss their future meeting with Macbeth, saying, "Fair is foul, and foul is fair" (1.1.12). What they mean is that good things are actually going to look bad, and bad things are going to seem good. Therefore, when they tell Macbeth that he is going to be king, it seems really good. However, it actually turns out to be quite bad because it drives Macbeth to find a way to make it come true. Banquo hits the nail on the head when he says that sometimes "to win us to our harm, / The instruments of darkness tell us truths, / Win us with honest trifles, to betray ’s / In deepest consequence" (1.5.125-129). In other words, the witches have told Macbeth one small truth -- that he will be named Thane of Cawdor (which has actually already happened; Macbeth just doesn't know it yet) in order to convince him to believe that the larger prediction is also true. In this way, they can deceive and manipulate him.
Later, when the witches conjure three apparitions, knowing that Macbeth is returning to them for information, two of the apparitions are absolutely deceptive. The second one says, "Be bloody, bold, and resolute. Laugh to scorn / The power of man, for none of woman born / Shall harm Macbeth" (4.1.81-83). This makes it sound as though Macbeth can never be harmed by anyone because every person alive was born of a woman. He takes it as an assurance when, really, it is just a craftily worded statement of fact.
Then, the third apparition says, "Macbeth shall never vanquished be until / Great Birnam Wood to high Dunsinane Hill / Shall come against him" (4.1.96-98). Again, this statement is designed to make Macbeth feel invincible because it seems impossible that the trees could uproot themselves and move of their own volition to Macbeth's castle. Therefore, he takes it as an assurance of safety when it is really just enigmatically worded. The sisters purposely deceive him in order to get him to let down his guard.