The Tempest is one of Shakespeare's most universal plays and, not coincidentally, is very much concerned with human behavior and emotion. As John Wilders observes in The Lost Garden, “Prospero’s island is what the sociologists call a ‘model’ of human society. Its cast of characters allows Shakespeare to portray in microcosm nearly all the basic, fundamental social relationships: those of a ruler to his territory, a governor to his subjects, a father to his child, masters to servants, male to female, and the rational to the irrational within the human microcosm itself" ([London: Macmillan Press Ltd., 1978], 127).
Prospero himself is an observer of and experimenter with human behavior: he saw human nature at its worst when his brother usurped his dukedom and sent Prospero and Miranda off to almost certain death; he has tried to nurture Caliban’s human half and to teach the monster acceptable human conduct; he demonstrates a working knowledge of reverse psychology when he maneuvers his daughter into love with Ferdinand; and, finally, he examines his own behavior and emotions in relation to his enemies, relatives, and friends.
Prospero and the play ask two questions: Is behavior such an Antonio's the basic nature of human beings; and, if so, can nurture improve upon nature? In modern terms, the play struggles with the ever-present debate over the impact of heredity and environment.
His first observations--of Antonio's and Alonso’s treachery--were inadvertent and even unexpected; however, they prompted Prospero to shift the focus of his studies from “the liberal arts” to human behavior. Prospero has devoted himself to gaining knowledge and, as he admits to Miranda, neglected his dukedom and perhaps even his own humanity; “His learning and the exercise of his occult powers make him god-like, but they also make him inhuman” (David L. Hirst, The Tempest: Text and Performance [London: Macmillan Publishers Ltd., 1984], 28).
Prospero’s two servants, Ariel and Caliban, are the first subjects of his experimentation. Terry Eagleton explains, “If Ariel needs to be tied down to the life of the body, the creaturely Caliban needs to be cranked up to the level of language. Ariel and Caliban symbolize, respectively, pure language and pure body, a freedom which threatens to transgress all restraint and a sensuous enslavement to material limit. Prospero strives to bring both of them within that dialectic of activity and passivity, bondage and transcendence, which for Shakespeare is prototypically human” (William Shakespeare [Oxford: Basil Blackwell, 1986], 95).
When he first arrived on the island and discovered Caliban, Prospero treated the monster “with human care” (1.2.346; all references to line numbers are from The Riverside Shakespeare, ed. G. Blakemore Evans [Boston: Houghton Mifflin Company, 1974]). He tried, with Miranda’s assistance, to educate and civilize Caliban, the offspring of a witch and an incubus, the very epitome of ignorance, bestiality, and treachery.
Caliban explains that Prospero taught him “how / To name the bigger light, and how the less, / That burn by day and night" (1.2.334 36), and Miranda says, “I pitied thee, / Took pains to make thee speak, taught thee each hour / One thing or other” (1.2.353 55). This particular experiment is an unfortunate failure: Caliban's reaction to learning language is to curse, and his responses to Prospero’s civilizing influence include attempts to rape Miranda and to kill Prospero. Prospero comes to the conclusion that Caliban is “a born devil, on whose nature / Nurture can never stick; on whom my pains, / Humanely taken, all, all lost, quite lost” (4.1.188 90).
One might argue, as Anthony Harris does in Night’s Black Agents, that Caliban’s “avowal that he will be ‘wise hereafter, / and seek for grace’ . . . with its suggestion that he is about to enter the first stage of the upward progression of the soul, comes when Prospero has apparently abandoned” his magic and his attempts to uplift Caliban ([Rowman and Littlefield: Manchester University Press, 1980], 131).
However, if Caliban has learned anything by the end of the play, it is only in relation to his island and potential usurpers. The only times Caliban actually admits to making mistakes are when he expresses regret for showing Prospero the island, saying, “Cursed be I that did so” (1.2.339), and when he sees Stephano and Trinculo for what they are, promising “to be wise hereafter” and exclaiming, "What a thrice-double ass / Was I to take this drunkard for a god” (5.1.295 97) .
Prospero finds more subjects for experimentation when his enemies sail within his sphere of influence. Once he has orchestrated the shipwreck, he scatters the passengers across the island, guiding Ferdinand to Miranda; leading Stephano and Trinculo to Caliban and into treason; and leaving Alonso with his own grief, Gonzalo's optimism, and Sebastian’s and Antonio's conspiracies.
Prospero finds little to recommend human nature through his experiments with these other people, sees no remedy for “natural” human corruption; and, furthermore, he observes no sign of penitence in Antonio, who has demonstrated that his “sin’s not accidental but a trade” (Measure for Measure 3.1.148).
But Prospero’s most important (and most successful) experiment involves himself. “Within Prospero himself . . . we glimpse intermittently the struggle, or internal tempest, between the humane impulse towards mercy and the instinctive appetite for revenge” (Wilders, New Prefaces to Shakespeare [Oxford: Basil Blackwell, 1988], 273).
Initially, Prospero is determined to avenge the wrongs he has suffered, but his revenge rarely takes a physical form. He is almost obsessed with inflicting emotional pain on Antonio, Alonzo, and Sebastian; although he expresses concern for the physical well-being of the ship's passengers in act 1, scene 2, Prospero is very much pleased with the maddening effects of Ariel’s tempest. The punishments Prospero inflicts on the “three men of sin” (3.3.53) are purely mental ones. The only people Prospero deliberately causes bodily harm are Caliban, Stephano, and Trinculo, and they are harmed only because they do not possess the sensibilities necessary to respond to (and learn from) intellectual discipline.
While Antonio, Alonso, and Sebastian may, under Prospero’s influence, regret their actions, it is unclear whether they have learned from their mistakes and have changed their natures, or whether they are merely more sophisticated Caliban, “Which any print of goodness wilt not take, / Being capable of all ill” (1.2.352 53).
Whatever the case, Prospero realizes, with Gonzalo’s tears and Ariel’s prompting (“Mine would, sir, were I human” [5.1.20]), that if he is to become fully human, he must forgive his enemies, abandon his magic, and return to his dukedom. With this realization, Prospero gathers everyone together for the final scene and makes a brave attempt at forgiveness and understanding.
Ultimately, Prospero discovers what it means to be human; the Prospero of the epilogue is the result of his own self-nurturing, his own proof that, in some circumstances, environment can triumph over (or at least counter-balance) heredity. He has recognized “the Ariel and the Caliban of which his own—and our—nature consists” (Wilders, New Prefaces to Shakespeare, 273); he has found the answer to the dilemma of nature vs. nurture in his own psyche, and with this knowledge he returns to the human society of Milan a more balanced, more complete human being than when he left it.