Measure for Measure is one of Shakespeare's tragic-comedies or 'problem comedies' as some have termed them. It comes from approximately 1603-4 although it was not published until the First Folio of 1623. The play causes difficulties for critics because its subject matter is sufficiently dark, morbid and even cathartic for it to be seen as a tragedy. Yet, many of the darker elements such as the imprisonment and the duke's impersonation of a holy man may not have been perceived in such a heavy and critical manner in the early seventeenth century. Measure for Measure as a story was derived from George Whetstone's play, Promos and Cassandra (1578) that was in turn taken from Cinthio's Hecatommithi. Its title is taken from Matthew 7:1, "Judge not that ye not be judged… and with what measure ye mete, it shall be measured to you again", and it provides the key to the play's message. The duke of Vienna is troubled by having to work with outdated and severe laws against unchaste behaviour when they seem in conflict with his own sense of mercy. So he pretends to leave the country to deputise his role to the stern and strictly principled Angelo, while the duke himself disguises as a friar. Caught up in these laws and machinations is Claudio who is accused of seducing his betrothed before they have wed. He is imprisoned and condemned so his loose living friend Lucio and his sister Isabella, a novice nun, plead to Angelo to spare his life. Angelo finds himself filled with lust for Isabella and in acts of great hypocrisy he tries to blackmail the girl into sexual favours for her brother's life. The duke intervenes and places Mariana, previously jilted by Angelo, in Isabella's place. Angelo acts worse still in failing to keep to his promise but the duke, revealing himself, in an act of compassion and mercy for his deputy spares his life. The play presents certain problems for the reader since it is not straightforward in its moral world of good and evil and is rarely comic in any modern sense, but it is a great play and an unusual one much in the same mode as Hamlet.