In Measure for Measure, Shakespeare takes characters and plays with their identity, to the point that most people in the play have dual identities.  The best examples of this are: the Duke, Isabella and Claudio.  This duality creates two sides to each person, and in some cases it creates a private side and a public side to each person.  In the case of the Duke he is a man of power, yet he does not like to be in the public eye.  He is lenient when enforcing lesser crimes and for the most part is considered to be a good man.  When he needs to enforce the law, he shrinks away, putting another man, Angelo into power to clean the streets.  The Duke disguises himself as a friar, a very private figure; one who is often isolated from the world within the walls of a monastery.  He plays both sides, and in doing so, avoids blame for any actions he may have done.

Isabella is Claudio’s sister, soon to become a nun.  She is called upon to help save her brother, Claudio, who has been imprisoned and sentenced to death for sexual relations out of wedlock.  Claudio asks her to try to use her feminine charm against Angelo, the man the Duke left in power in his absence.  He hopes that she will do anything to save the life of her brother.  It is revealed that the only way to save Claudio’s life is for Isabella to sleep with Angelo.  Being a woman of God, she refuses, and the friar (Duke in disguise) suggests pulling the “bed trick”.  This entails switching Isabella for someone else; in this case it is Angelo’s fiancée Mariana.  This swapping is yet another instance of hiding someone’s identity in hopes of coming out of the situation untouched.

Finally, we have Claudio, who has been sentenced to death.  He is in jail and begged his sister to help him.  The bed trick was successfully pulled off, yet Angelo did not keep his word, as a result Claudio was to die by morning.  The Duke in disguise comes in and suggests yet another swap.  This time, they will say that Claudio has been beheaded, but they will send the head of a pirate in its place.  Then Angelo will be satisfied and Claudio can escape/be released once the Duke returns (receiving a pardon).  One of the themes of this play is concealing identity in order to avoid a punishment.  In other words, they don’t want to become victims and face the law, whether it is an eye for an eye, or as Shakespeare put it, measure for measure.