What immediately strikes the audience about The Tempest is the use of the supernatural in the form of apparitions like Ariel and the Harpy. These apparitions are under Prospero's authority and the result of his Art, which is the disciplined use of virtuous knowledge. By invoking a masque to celebrate the betrothal of Ferdinand and Miranda, Prospero effectively brings to full circle the theme of re-generation by obliterating the evil done and suffered by one generation through the love of the next. However, this is juxtaposed against the anti-masque elements of the attempted usurpations of Antonio and Caliban, which hold the play in a delicate balance between a tragic or comic resolution, holding the audience in great suspense.
Through the use of his Art, Prospero is able to bring Ariel, whom he releases from the imprisonment of Sycorax, under his control. By transcending into the realm of the supernatural, there is an inversion of the Natural Order, as Prospero is but a mere mortal while Ariel is beyond humanity at the spiritual end of the natural hierarchy. However, the authority that Prospero possesses over Ariel is liable to abuse. There would be a very human temptation for him to use Ariel to exact his revenge on the Court Party members, who are effectively at his mercy, because of an inherent susceptibility to feelings of resentment, anger and revenge due to the injustice of 12 years past. This is Prospero's test as a ruler, not only in his treatment of the Court Party but also in his treatment of Ariel. He must exhibit benevolence and temperance before he can pass this test. Initially, there are lapses in Prospero's control over his anger when, as Ariel asks for his freedom, Prospero replies with a harsh "if thou more murmur'st, I will rend an oak, and peg thee in his knotty entrails, till thou has howl'd away twelve winters." Thus, it is only when Prospero has the qualities necessary to rule, by controlling his passions with reason and always remembering that his purpose is the education of the Court Party and not revenge, that he can win the respect of the audience and earn his journey home.
This "brave spirit", Ariel, is a minister of Order and Providence. By being omniscient, he not only allays the initial tempest through his music, but he also undermines the plots against human life -- Antonio and Sebastian's attempt at Alonso's life and Caliban's murder plot. On a lighter note, Ariel also acts as a source of great entertainment for the audience as he goes about his work for Prospero, especially when he proceeds to undermine Caliban's murder plot with great relish and excitement as he leads the intoxicated conspirators through a "filthy mantled pool", symbolic of their bestiality.
The juxtaposition of a spirit of the elements with a creature of the earth in the form of Caliban brings out the bestiality of this deformed brute. The subjugation of both creatures is...