The phrase "fair is foul, foul is fair" is a paradox that sets the stage for the entire play of Macbeth. It is first uttered by the witches in Act 1, Scene 1, and then echoed by Macbeth in Act 1, Scene 3. The phrase means that appearances are deceiving, and what appears to be fair is actually foul, and vice versa. It is a motif that runs throughout the entire play and essentially means that good is bad and bad is good. The witches use this phrase to introduce themselves to Macbeth and to foreshadow the events to come within the play. The phrase highlights the hypocrisy that people adopt to hide their true intentions and warns about judging things based on their appearance. The theme of fair is foul and foul is fair is prevalent in Macbeth, and Shakespeare uses it to show that what is considered good is actually bad and what is considered bad is actually good.