Supernatural is any “phenomenon which can’t be explained by the accepted laws of natural science or physical laws.” There is a reason that the play Macbeth begins with the three witches.
There is no direct mention of any real character of the play in Scene I, Act 1 but it is in such a supernatural happening, the primary contradiction inherent in the play is uttered when together they say, “fair is foul, and foul is fair.”
As if through such outer metaphysics the true meditation on the themes of the play is possible. Macbeth is introduced in the play only after the three witches utter, “a drum, a drum! Macbeth doth come.”
And Macbeth reiterates what earlier the three witches uttered. This is where we come to understand the supernatural side to the real happenings in the play.
The three witches seem like knowing much more than they actually say every time they surface in the play. Each word they utter has a solid contribution to Macbeth’s action.
Their presence is more involving to the entire plot because apart from Macbeth, Banquo can also see them. The fact that he disqualifies the evil they try to inspire in him tells us of his clear conscience.
The witches might’ve been based on popular superstition of that time but they are beings with power more than mere witchcraft. What they utter confirms the evil which has been in the heart of Macbeth. Macbeth surrendering to the suggestions made by their prophecies binds him to a tragic fate beyond his power to prevent it.
His second meeting with them makes him bloodier than ever before because he has already confirmed to their suggestive trap by murdering Duncan and Banquo. It is their misleading apparitions which tempt the natural temptation in him due to unchecked ambition.
The three witches are such supernatural beings whose words have realistic consequences carried out by Macbeth like human individuals. Shakespeare makes them vague in their foretelling and that’s what makes them sound so persuasive to the conflictive Macbeth.
The ghost of Banquo is another supernatural presence in the play but its presence is of a different degree. Here it is a psychological consequence, a sign of Macbeth’s inner weakness to the constant poking of his conscience, his deep-seated guilt.
Shakespeare uses the ghost in a supernatural tone to unsettle Macbeth from the leftovers of his ambitious strength. Shakespeare diving deep into the psychology of his characters uses supernaturalism to treat them more objectively. Supernaturalism is the theme which brings out the theme of power and guilt in the play much clearly.