The Tempest Theme of Betrayal

Loyalty and betrayal are linked to The Tempest's larger themes of servitude and freedom; either feeling is motivated by how each individual perceives his position relative to others. Antonio's betrayal of his brother and theft of the dukedom of Milan are the source of conflict in the play, but the action contemporary to the play follows a series of attempted betrayals. Alonso and Prospero would both be murdered by traitors, but this is thwarted by the actions of loyal characters like Ariel and Gonzalo. Loyalty and treachery also serve as the two main personality traits of the players. You can separate the loyal out, and divide the bad into those who were misguided and now repentant, and those who are just plain evil. 

1. Gonzalo is arguably the most loyal character in the play, though he doesn't stop anyone from exiling Prospero. He's also doggedly loyal to Alonso, who aided in Prospero's betrayal. Does Gonzalo's sympathy mean anything?
2. What is the turning point for Sebastian, after which he is willing to murder Alonso? Is it Antonio's persuasion, or some seed that must just be part of Sebastian's character? (Think of Macbeth and the "influence" of the three witches.)
3. Was it disloyal of Antonio to take over a dukedom that he effectively ran anyway, especially if Prospero was never doing his duke-y duties? How much of this betrayal is Prospero's own perspective and convenient forgetting that Antonio was doing all the hard work?
4. The Tempest is the origination of the phrase "what's past is prologue." What does this kind of mentality say about opportunities in the present? Can one really have loyalty built on old ties when so much is new?

Loyalty is a farce in the play; everyone follows the courtly rule of swearing loyalty, but gives up on the notion as soon as it is no longer convenient.

Antonio's betrayal of Prospero reminds us that even family members cannot be counted on to be loyal.