Macbeth

In my opinon, Lady Macbeth is not the fourth witch.... she is a woman. From the start, she worries her husband won't be ambitious enough to fulfill the prophecy. She has no supernatural powers. In fact, she calls on spirits in order to make herself capable and cruel..... to give her the powers of manipulation she will need to convince Macbeth.

Come, you spirits
That tend on mortal thoughts, unsex me here
And fill me, from the crown to the toe, top-full
Of direst cruelty! ...
Come to my woman's breasts,
And take my milk for gall, you murdering ministers,
Wherever in your sightless substances
You wait on nature's mischief!