The poem begins with a section in brackets, in which Caliban, the creature from Shakespeare's The Tempest, introduces himself. He crawls on his belly along the island on which he is trapped, talking to himself freely since his masters Proper (Prospero in Shakespeare) and Miranda are asleep. He heads for a cave.
From here, he begins his main address, which is about Setebos, the being he considers his God and creator. For Caliban, Setebos created the world from "being ill at ease," as an attempt to compensate for his cold, miserable existence. Because Setebos could not make himself a peer, a "second self/To be His mate," he created a miserable island of lesser creatures that "He admires and mocks too."
Caliban, in imitation of what he believes Setebos to be, gourds a fruit "into mash," in effect acting as a creator himself. He imagines if he could "make a live bird out of clay," he might watch indifferently as that bird "lay stupid-like," unable to fly. He is imagining himself showing the same indifference to the fate and happiness of his potential creatures as he imagines Setebos shows to him.
Not only does Caliban believe Setebos to rule without any moral sense, he also believes Setebos is entirely unpredictable, liable to cause pain for an offense that he had otherwise approved of. Caliban does wonder whether he simply might not understand the ways of Setebos, but also notes that Setebos took pains not to create any creatures who, even if they might be "worthier than Himself" in some respects, would have the power to unseat Setebos from his godly place.
When Caliban considers why Setebos would be so unhappy to have created an unhappy world, he conjectures that perhaps Setebos is Himself a subordinate to a power that He does not understand. Calling this greater power "the quiet," Caliban describes it as one "that feels nor joy nor grief,/Since both derive from weakness in some way." Driven by resentment over not having a connection to His own maker, Setebos must have angrily made the Earth "a bauble-world" where nothing makes sense.
Caliban next thinks on Prosper, his magician master on the island. He play-acts as Prosper, using other animals to create his own hierarchy where he is the master over others. From this experience, Caliban considers that perhaps Setebos created the world not from any strong emotion or feeling, but rather for the sake of work itself, to "exercise much craft,/By no means for the love of what is worked." That the world might one day fall down does not matter under this line of thought, since the work can simply be repeated.
He returns to thoughts about Setebos's unpredictability, citing how "one hurricane will spoil six months' hope." What's more, Caliban cannot rationalize why he would be so hated while Prosper would be so blessed by the deity. Caliban holds some hope that the world might get a chance to improve itself and become less built on random destruction and misery.
The best way to "escape [Setebos's] ire," Caliban believes, is to feign misery. He believes that showing Setebos happiness is sure to bring pain down on oneself, and so Caliban only dances "on dark nights," while he at other times works to look miserable and angry. He will stay committed to this plan until Setebos is either taken over by the quiet or dies on His own.
The final section is again bracketed. As a storm begins, Caliban sees a raven flying overhead and fears that the bird will report his musings to Setebos. Worried he will be punished for revealing happiness and expressing impertinence, he immediately resumes his guise of a miserable beast.
This dramatic monologue, published in 1864 in Dramatis Personae, is arguably one of Browning's most sophisticated. Its fundamental questions are theological, as it contemplates both the origins and motives of divine power, and by extension what humans are capable of understanding about their world and the forces that control it. The blank verse allows Caliban's rambling but observant thoughts to create a memorable voice that blends misery and perception.
There are a few historical and literary influences that should be noted. The most immediate is Shakespeare's The Tempest. In the play, the wizard Prospero is stranded on a wild, magical island with his daughter Miranda and certain creatures he commands through his magic. One of these is Caliban, a miserable humanoid who finally commits to seeking grace in the end. Browning co-opts this creature for several reasons, not least of all because he is defined by his misery. He views himself as lesser (and objectively is a less sophisticated being than the humans), and is unhappy to be under Prospero's direct control. Using this creature as a vantage to explore our own relationship to a divine power not only creates higher drama and stakes, but also imbues all the considerations with a cynicism.
The immediate historical influence on the poem is the then-recent publication of Darwin's Origins of the Species. Browning was responding to several naturalist theories that surfaced in the face of the scientific realization that man might not be a direct and divine creation. The first of these theories is that God could be understood by natural, empirical evidence. The second is that God must not exist in the image of man if we have evolved from animals and hence are not directly in His image. There are two pieces of corroborating evidence that suggest Browning was exploring these ideas. One is the epigraph to the poem – "Thou thoughtest that I was altogether such a one as thyself" – taken from Psalm 50 in the Bible, and spoken by God to wicked sinners who thought the deity wicked like themselves. The second piece of evidence is the poem's subtitle: "Natural Theology in the Island." This would certainly have resonated with scholars and educated readers of the time as being relevant to the then-current theological debates following the revelations popularized by Darwin's study.
So the questions Browning asks through this monologue are all centered in these contemplations, though it should be noted that with his characteristic sophistication, Browning does not suitably answer any of these questions with certainty. The monologue has dialectical possibilities, and one should read it as a consideration of various possibilities instead of as a philosophical tract. That Caliban has a firm idea of Setebos should not keep us from doubting his beliefs and investigating what has influenced him to understand Setebos the way he does.
First should come an analysis of Caliban himself. Unlike the creature in Shakespeare's play, Browning's Caliban has a remarkable degree of self-consciousness. Perhaps the most telling quality of his monologue is his tendency to address himself in third person. It's a childish construction for the creature to use, but it also reflects his belief that Setebos will punish him for showing any happiness and joy. He is intelligent enough to realize that his true identity is divorced from his behavior, and as such disassociates himself so he can study himself objectively. It's a Freudian construction, a superego judging an ego. One other element of Caliban is his delusional ability to justify his own limitations. Those limitations are physical – he's a humanoid creature – and circumstantial – he has to serve a cruel master, with his only release being when Prospero is asleep. In many ways, one can argue that Caliban feels compelled to create Setebos so as to justify his misery. If Setebos is responsible for fashioning a terrible world, then it is justifiable that Caliban himself is miserable.
And indeed, the Setebos he imagines is a pathetic and miserable creature. Like the Victorian naturalists, Caliban does not piece together his sense of a god from an inner feeling, but instead from empirical evidence. Notice the amount of this long poem that is devoted to categorizing creatures, describing them in grotesque and miserable terms. The repeated phrase "So He" suggests a scientific construction, in which Caliban paints his God based on observation rather than any a priori considerations. Based on such a miserable island, Setebos is imagined as a spiteful and resentful creature who creates not to punish others or please himself, but rather to exercise his ambivalence. He creates simply because it's something to do, to distract Himself from "the quiet," His own deity and one He cannot understand, all with little care for the concerns of those He creates. There are no moral concerns in Setebos, even though Caliban imbues Setebos with emotions. Because these creatures exist below Setebos, it is not in his perspective to be concerned with them.
Caliban's entire worldview is based on hierarchy. As a creature under Prospero's control, it is likely comforting to imagine that Prospero himself is controlled by Setebos, and further, that Setebos is controlled by "the quiet." It is only at this highest level that Caliban stops conjecturing, and proposes a creature that "feels nor joy nor grief," in effect having no emotions at all. For a creature punished by the world, it must be nice to think that the ultimate power does not even have room for feelings, since that suggests those feelings are ultimately irrelevant. Further, Caliban exercises his own power over smaller creatures, both physically when he grinds the fruit down or pretends that the snake is Miranda, and imaginatively when he thinks about creating a bird from clay. The irony of Caliban's hierarchy is that he creates his conceptions of those above him using empirical evidence from below. That is, the creatures with superior power are actually dependent on what is below them (or at least Caliban's perception of those things below them), which naturally limits them to Caliban's perceptions. In other words, Browning suggests through Caliban's empirical methods that no matter the imagination of he who derives God this way, God will always be no bigger than what that person sees and does. A miserable creature will create a miserable God, and so by default a happy man will do the opposite.
Overall, this poem is a study of a masterful interpreter, one who attempts to make an order of his world. He studies behavior (including his own) in order to create a system that can then dictate his behavior. It is telling that he ends the poem by again pretending to be miserable, but it is only perceptible to us (through dramatic irony) that these rules are of Caliban's own imagining. The vicious circle of an empirically created God ultimately leads to man living through a lack of imagination, creating his own self-fulfilling prophecy. That Browning disapproves of or at least has pity for such a worldview is apparent – but what worldview he deems superior, or even how he perceives God, is not clear. Instead, what is admirable in the poem is the quest of self-analysis and thought.