In Act 3, Scene 2, the Duchess and Antonio have been secretly married and are about to act on their plans to flee the court together. In a court scene rife with dramatic irony, their final interactions are colored by the audience’s knowledge of their secret scheme. However, because the members of the court around them do not know of their love, their conversation (and Antonio’s dismissal) is full of double meanings and secret nods to their shared affection. The scene’s dramatic irony creates a sense of tension.
Because the Duchess and Antonio are acting against the Cardinal’s wishes, there is a sense of danger in their ploy to escape. Because many of the lines from this scene have multiple meanings, the audience has a growing sense of their proximity to this important, deadly secret. Antonio’s exit line is a good example of how dialogue functions doubly because of the dramatic irony. Before he leaves the stage, he says:
You may see, gentleman, what 'tis to serve
A prince with body and soul.
On one level, Antonio seems to be remarking on his dismissal despite years of service. He has been faithful to the Duchess, and, from the perspective of the court, his loyalty hasn’t saved him from a swift departure from her grace and influence. However, the audience and lovers know differently, and can therefore pick up on Antonio’s vow of devotion to the Duchess. His use of the word "serve" implies a double, more sexual meaning that helps the audience understand his parting words in a new light. In actuality, Antonio is binding himself to the Duchess as her servant in love and devotion, and as soon as the audience realizes this, they become hyper aware that they’ve picked up on a level of meaning unknowable to the other characters present.
In Act 4, Scene 1, Ferdinand and Bosola play a trick on the Duchess that creates a moment of dramatic irony that ultimately leads to some foreshadowing. The Duchess is tricked into thinking that Antonio and her children have been killed, and she is devastated by the apparent loss of her family and spouse. However, the audience knows ahead of time that Antonio is still alive.
The tension of the moment, and the desperation of the Duchess’s response, is therefore affected by their knowledge of the deception at hand. As a result, the audience comes to feel a sense of desperation and helplessness; they cannot help the Duchess nor make her aware that she is being misled. This tension is heightened during a particular piece of the Duchess’s dialogue. After Bosola tries to comfort her, she responds:
That’s the greatest torture souls feel in hell:
In hell that they must live, and cannot die.
The severity of the Duchess’s response is an important part of the dramatic tension created in this scene. She expresses her wish to die because the idea of living without her family is torturous to her. The audience cannot experience the extent of her pain without the understanding that it is in vain. In fact, the Duchess’s family is still alive and her desire to die would carry her from them. The Duchess’s reaction to the supposed death of her husband and children also foreshadows, for the audience, how her brothers’ trickery will ultimately give the Duchess the power. Because she would rather die than live in the world without her family, she makes it impossible to take anything else from her.
