the poniard

Act 3.2.150-155
Since the Duchess has "shook hands with Reputation", according to Ferdinand, he claims that he will never see her again. Then he leaves her with the poniard, perhaps so that she may kill herself. Its interesting that he wants to fix her sins, with sins. However, marrying and having children, although with a man bellow her station and rank, is not really a sin. Whereas, suicide would be a sin and would forever affect her present life and her afterlife. What is also interesting to point out, is that in lines (Ferdinand's little speech) 122-139, Ferdinand seems to give the Duchess masculine qualities. A man has the ability to choose to leave Reputation. The Duchess, in his opinion, purposely left and decided instead to go to love (where only lowly unambitious people with no money go). She took control over her own fate to leave (masculine), which seems to bother Ferdinand the most. It's not about her reputation in the end, its about the power she has to have made this decision. He doesn't care if it was "sinful", because you would not combat sin with sin.