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

Macbeth's very opening line is "So foul and fair a day I have not yet seen" :so many men have been slaughtered in battle, yet he has achieved a great victory.

The words are echoed by the witches in the form, "Fair is foul, and foul is fair: / Hover through the fog and filthy air". Witches at that time were creatures of the night and the devil. They gravitate to what is "foul" and shun the "fair" (as Dracula hides from the sun centuries later). They depart, to"hover" in the fog, and in the dust and dirt, waiting for their chance to do further evil. The very fact that they incite Macbeth with their 'prophesies' of future greatness - which as soon as Lady Macbeth hears of it, incites her to plan to kill Duncan) - is an instance of how they spread evil. Look at how these foul, loathsome, ugly creatures are yet the source of and impart such 'fair' tidings to Macbeth in the way of their 'prophesies'.

A day foul, yet fair for Macbeth; for witches, fair is foul and foul is fair” The truth of this paradox is woven throughout the play, in how situations appear to be good when in reality they are evil (or vice versa). All people have the capability of being good and appearing evil as well as being evil and appearing good.