measure to measure

From the beginning of the play the Duke shows his fascination with the art of disguise. He has Lord Angelo takes his place and he in turn becomes a friar in disguise. Throughout the play this notion of false identity and exchange of identity plays an important role for the Duke and also for the characters in the play.
To understand why the Duke has this desire to disguise himself one can look at the beginning of the play in act 1 scene 3 where the Duke is at the monastery asking Friar Thomas to hide him there. He tells the friar that he has good reasons for hiding, and that he has lied to Angelo about his destination. The Duke explains that for the past fourteen years the laws have been flagrantly disobeyed, with little reproach from the government. As the Duke explains it, when the law only serves to threaten, because lawmakers do not carry out the punishments dictated, the government loses its authority. Since he gave the people liberties, he does not feel comfortable punishing them for now, yet he worries about the safe affairs of Vienna. He asked Angelo to take over in order to act more strictly without reproach or hypocrisy. He wants to observe Angelo at work, so he asks the friar to provide him with a disguise which will make him look like a visiting Friar himself:
And to behold this sway,
I will, as’twere a brother of your order,
Visit both price and people: therefore, I prithee,
Supply me with habit and instruct me
How I may formally in person bear me
Like a true friar. More reasons for this action
At more leisure shall I render you;
Only, this one: Lord Angelo is precise;
Stands at a guard with envy; scarce confesses
That his blood flows, or that his appetite
Is more to bread than stone: hence shall we see,
If power change purpose, what our seemers be.

Overall the Duke is a good natured person who is and virtuous and kind hearted. He wants what is best for what is around him. He also wants to bring more law and order to Vienna but does not know how to do it himself so therefore he appoints Angelo. However he does not wish to have him free reign, knowing that he is very strict. Possibly the Duke feels that he is weak in power himself in maintaining order and in his heart he feels the only way to truly see how the people of his city will act is to be in disguise. And this is considered to be true when he discloses his identity because many problems are resolved. We can see this in Act 3 scene 2 when the Duke encounters Lucio and shows himself to be mildly vengeful, trying to protect his honor despite his disguise. This perhaps, suggests an ulterior motive in disguising himself: he ants to see how his subjects rule, and he can only do so through making himself functionally invisible to them.
Not only does the Duke have a false identity, technically so does Lord Angelo. He is only appointed to take the Duke’s place he himself is not a real Duke. Throughout the play because of his strict ways he himself likes the idea of all the power and the ways that he can enforce it. He keeps hidden his contract to marry Mariana and in the end is faced with his secret. Angelo is told to marry Mariana, and he escapes death at her request. The Duke probably does not intend to execute Angelo but wants it made clear that his crime deserves such a punishment.
The Duke, in his disguise, also advises other characters to carry out two other secret plans involving mistaken identity. He has Mariana take Isabella’s place ( Act 3 scene ) , and he also has the head of a dead pirate is sent in the place of Claudio’s.
Throughout the play in keeping with character’s false identity and so his own identity the Duke some time must reveal his own. He does not immediately do this because his is still enjoying the intrigue which he can only understand. To some extent his is