Contrast Prospero's attitude towards Ariel and Caiban

Prospero uses his magic to control both Ariel and Caliban, albeit in different ways. In that sense his attitude towards them is inherently exploitative. Ariel and Caliban exist to serve him, and how they perform their duties will largely determine how they are treated. Caliban, for instance, is treated by Prospero in a malicious, vengeful manner. Prospero's magic is used to control Caliban, to keep him in a permanent state of subjugation. It's no wonder that Caliban is so surly and resentful towards his master. But ultimately he has no choice; through the exercise of his magic powers Prospero has a hold on him:

I must obey. His art is of such pow’r It would control my dam’s god, Setebos, And make a vassal of him (Act I Scene ii).

It's different with Ariel. Whereas Prospero uses his magic to subjugate Caliban, he uses it to set Ariel free from the curse of Sycorax, the evil witch. Because of this, Ariel adopts a submissive posture towards Prospero; he feels forever in his debt. Even so, Ariel makes so bold as to ask his master if he might one day be released from his authority:

Is there more toil? Since thou dost give me pains, Let me remember thee what thou hast promised, Which is not yet performed me . . . My liberty (Act I Scene ii).

Yet Prospero immediately puts Ariel back in his box. He threatens to imprison him in an oak tree for twelve years. Wisely, Ariel reverts to his supine attitude:

Pardon, master. I will be correspondent to command And do my spiriting gently (Act I Scene ii).

So even though Prospero has a more benevolent attitude towards Ariel, he still makes it abundantly clear that he is firmly in charge. Until he's finally granted his liberty, Ariel's relationship to Prospero is characterized by domination and control no less than Caliban's.