One of the major themes in the play has to do with Macbeth's ambitious desire for power. He understands that it is morally wrong to kill and perform other ill acts to attain power; however, Macbeth convinces himself that he must press forward to get what he wants. At the beginning of Act 2, Macbeth hallucinates the dagger which is a motif for the sense of fear and guilt that Macbeth feels over his plan to murder King Duncan. In his soliloquy, Macbeth says, "A dagger of the mind, a false creation, proceeding from the heat-oppressed brain?" (II.i.38-39). Later in the play while all are at the banquet and Macbeth hallucinates Banquo's ghost, Lady Macbeth refers to the "air-drawn dagger" because Macbeth is again expressing his guilt over having murdered to satisfy his greed and ambition.