what is the meaning of fair is foul, and foul is fair, Hover through the fog and filthy air.

These are part of the lines spokenby the witches at thebeginning of theplay, helping to create the atmosphere of tension and evil as they await their meeting with Macbeth.

The oxymoron that is used 'fair is foul and foul is fair' is foreshadowing the deception that the witches will use with Macbeth. He will believe that their prophesies will lead him to greatness, but they will in fact destroy him.