What was Big Willy Shakes going for?
For all of this to make sense, we should tell you that Caliban isn't your average islander. In fact, he's one of the most debated figures in all of Shakespeare. As the island's only native, Caliban showed Prospero how to survive on the island and Prospero took Caliban under his wing and taught him to speak. For a while, things were hunky dory.
Or, as hunky dory as things can possibly be on a remote island. We even learn that Prospero treated Caliban "with human care" and let him stay at his pad.
So what changed? Why does Prospero enslave Caliban, punish him with debilitating stomach cramps, and hurl the kinds of insults that would have most of us running to the bathroom to cry? Well, Caliban, we learn, tried to rape Miranda in an attempt to "people" the isle with a bunch of little Calibans (1.2.4). That's pretty inexcusable, so it's clear we're supposed to be repulsed by Caliban's monstrous behavior and it's easy to see why Prospero treats him like dirt, even if it makes us a bit squeamish.
So when Prospero calls Caliban a "mis-shapen knave," "demi-devil," and "bastard" in this speech, we get why he's so ticked at the creature who just tried to murder him and rape his daughter, Miranda.
We should mention that there's another side to this story. For a lot of critics, Caliban is symbolic of what happened to victims of European colonization in the centuries after Shakespeare wrote The Tempest. We think Virginia Mason Vaughan and Alden T. Vaughan do the best job of summing up this argument:
Caliban stands for countless victims of European imperialism and colonization. Like Caliban (so the argument goes), colonized peoples were disinherited, exploited, and subjugated. Like him, they learned a conqueror's language and perhaps that conqueror's values. Like him, they endured enslavement and contempt by European usurpers and eventually rebelled. Like him, they were torn between their indigenous culture and the culture superimposed on it by their conquerors (Shakespeare's Caliban: A Cultural History).
This interpretation of Caliban can be pretty powerful and socially relevant, especially in film and stage productions where Caliban is portrayed as a colonized, New World subject. Yet, it's also important to remember, as Vaughan and Vaughan point out, that this "interpretation of Caliban is symbolic for what he represents to the observer, not for what Shakespeare may have had in mind."
If we're using this interpretation of Caliban, then we can't help but notice how Prospero's "thing of darkness" comment is a real slam on colonized people. This quote shows us how Prospero has taken Caliban's island for himself, and then oppressed the guy as a slave, even though Caliban is originally from there.
Hmm… sound familiar? That's pretty much how most New World stories begin. If we take it a step further, we'll see that even that Caliban's name is an anagram or at least a play on the word can[n]ibal, a term derived from "carib" (as in the Caribbean). This was a European term used to describe flesh-eaters. If this is the case, then Caliban's name associates him with the kinds of so-called savage man-eaters that Europeans were reading about in travel literature when Shakespeare wrote the play.
It's also possible that Caliban's name may be a play on the Romany word "Cauliban," which means "black" or something associated with blackness. This makes some sense, especially given that Caliban is associated with darkness throughout the play. By the way, literary critic Kim F. Hall points out that Caliban's association with "darkness and dirt" is the opposite of Miranda's association with purity and light.
Whichever interpretation you believe, we think we can all agree that Prospero's not offering his mutant slave a compliment here.