DAVINA: Not all literary critics have approved of the presence of these supernatural witches. One who didn’t was Samuel Johnson, often referred to as Dr. Johnson, who lived about 150 years after Shakespeare, and has been described as one of the most distinguished man of letters in English history.
RALPH:  Johnson lived in a period known as the The Enlightenment, or the Age of Reason – a period when modern science, with its emphasis on empirical evidence and rational logic, discredited the belief in superstitions like witchcraft.
DAVINA: So Johnson argued that if Macbeth had been written during his time, Shakespeare would have been banished from the theater and sent to write fairy tales instead of great tragedies.
RALPH: The first half of the 19th-century brought the Romantic period, which was a reaction against the Age of Reason and scientific rationalization. The Romantics placed an emphasis on the emotional and imaginative qualities in each individual.
DAVINA: The great Romantic poet and critic, Samuel Taylor Coleridge, approved of Shakespeare’s witches. It didn’t matter if they were real or not; they tapped into the audience’s fears, and represented the shadowy, obscure, and lawless part of human nature. Through the witches, Shakespeare makes visible what’s so disturbing in Macbeth’s character. 
RALPH: Another Romantic critic, William Hazlitt, agrees. He sees the witches as a device used by Shakespeare to set a tone of unnaturalness and darkness, which is crucial to the dramatic success of the play.
DAVINA: And not every critic agrees that these characters are supernatural in the first place.­ According to A.C. Bradley, an Oxford professor and the preeminent Shakespeare scholar at the beginning of the 20th century, “The witches are not goddesses, or fates, or, in any way whatever, supernatural beings. They are old women, poor and ragged, skinny and hideous, full of vulgar spite.”
RALPH: According to Bradley, a modern audience does not need to suspend its disbelief in witches, because Shakespeare has only portrayed these characters as what accused witches really were in their time –  hideous, spiteful, old hags who had been falsely accused of witchcraft by their ignorant neighbors.