If you just go down the Dramatis Personae of The Duchess of Malfi, you're already looking at a complex web of duty relationships, which are made even more complicated by the events of the play. Antonio, for instance, is responsible to the Duchess as her servant, but once he marries her he must both retain his duties as her employee while also becoming her "overseer" (1.1.375) as her husband. Yikes.
The Duchess of Malfi fixates on the relationship between prince and servant, and presents us with multiple versions of that relationship, ranging from the good (the Duchess to Antonio) to the bad (Bosola to the Duchess) to the ugly (Ferdinand to Bosola). Our play doesn't just deal with social and political duties, though. It's also all about domestic ones. You could easily describe the main conflict of the play as the collision of the traditional duties of a woman to her male relatives with those of a free prince.
Questions About Duty
There are several different examples of what various people think the relationship between a prince and his courtiers should be—think about what they are. Do you think that any one of them is shown to win out in the end?
What are the Duchess's obligations to her brothers? Her people? Her children and Antonio?
Does the Duchess fail in her duties to her subjects by marrying Antonio and thereafter conducting her private life in total secrecy?
What are the various duty relationships at work in the character of Bosola? He's employed as a spy for Ferdinand while working for the Duchess and her court and references, in various ways throughout the play, his inability to serve himself. What's up with this mess?
Chew on This
By making Antonio both her steward and her husband, the Duchess puts him in a socially impossible position.
Webster ultimately shows that a healthy relationship between prince and courtier isn't possible. Sorry folks, no dice.