Macbeth is thought to have been first performed in 1606, for the visit of the Danish king to James I. It is therefore likely that not only was James I's Scottish ancestry reflected in the play, but also his interest in witchcraft and the supernatural. In order to please the king, Shakespeare made the influence of the supernatural element on both the course of Macbeth's downfall and the dramatic tension of the play significant.
The fact that the Witches open the play is not only visually effective on stage, but it also foreshadows the importance of their role - and that of the supernatural. They combine to chant "Fair is foul, and foul is fair;/ Hover through the fog and filthy air." The paradox of "foul" and "fair" introduces the theme that everything is not as it seems in Macbeth, a theme borne out through the deceptive behaviour of Macbeth and Lady Macbeth, and also through the equivocation of the Apparitions later in the play.
The importance of the Witches' influence is directly signposted early in the play when Macbeth's words 'So foul and fair a day I have not seen', echo theirs. We are left wondering if they have already placed a supernatural charm on him. The "fog' in the chant is also dramatically interesting for the audience as it contradicts the opening stage direction, "Thunder and lightning", as fog and lightning are conflicting weather systems that do not appear together.
This strange atmosphere is intriguing to the audience and foreshadows the strange occurrences discussed by Ross and the Old Man in Act II, Scene iv when a mousing owl killed a hawk and Duncan's horses are said to have eaten each other. Shakespeare uses the pathetic fallacy of these supernatural occurrences to bring out the idea...