The Shakespearean version of the story is different from the sources in several significant ways. It is a milder handling. For example, Angelo views the supposed head of Claudio himself, while his counterparts in Cinthio and Whetstone send the evidence of execution to the sister. Isabella pleads for Angelo before she learns her brother has been saved, while in Whetstone and in Cinthio's second version, the heroine only begs mercy for the magistrate upon learning of her brother's safety. Escalus is invented by Shakespeare to offer a dramatic contrast to Angelo. The humorous minor characters and the secondary action of which they are a part are Shakespeare's own.
But there are three major ways in which Shakespeare's version is at variance with the sources. First, the duke plays a major role in Measure for Measure, while his counterparts in the sources are merely introduced at the last minute to provide a solution to the conflict at hand. The duke's disguise, his manipulations of the other characters, and his proposed marriage to Isabella are all new in the Shakespearean version. Second, Isabella refuses to sacrifice her virginity to Angelo. She places her virtue above her brother's life. Her action presents a marked contrast to the background of moral corruption against which it occurs. As a result, the whole business of the substitute bed partner and the character of Mariana are introduced. And third, Shakespeare's heroine does not marry her tormentor. Isabella's virtue is paired in the final scene with the duke's goodness rather than with Angelo's vice.
