Show how dramatic irony contributes to the development of the plots and characters in The Merchant of Venice in at least three significant places.
The biggest example of dramatic irony in this play comes in the famous court scene in Act IV scene 1, when the audience knows that the lawyer trying to persuade Shylock to show mercy is actually Portia. This disguise is so effective that even Portia's new husband, Bassanio, does not recognise her. This is significant for a number of reasons. Firstly, it clearly shows Portia's intelligence and strength of character. Antonio's case is shown to be a problem that nobody is able to solve or find a resolution to except to go with Shylock's bond. Portia, however, is shown to find a solution where nobody else can, thus strengthening her character and showing her to be incredibly resourceful and intelligent.
However, this scene also adds humour to the play. At the end of Act IV scene 1, Portia demands the ring she recently gave to Bassanio as a token for her labours in freeing Antonio. Note what she says when she asks for this token:
And (for your love) I'll take this ring from you--
Do not draw back your hand, I'll take no more,
And you in love shall not deny me this!
There is intense irony in these words. Note the way that Portia repeats the phrase "your love" and "in love." Clearly Portia is playing with the dramatic irony here: the audience knows that she is in fact Bassanio's wife, and therefore he is giving her only what she deserves because of his love for her. At the same time, however, the audience has seen that Portia told Bassanio to never part with the ring that she demands him to part with now, and this is something that causes great humour as the lovers are reunited in Act V scene 1, and both Nerissa and Portia upbraid their husbands for their lack of fidelity before revealing all. These examples of dramatic irony therefore allow women to be dominant and to upstage their male counterparts in this play.
Dramatic irony occurs when the audience of a play knows what the characters in the play do not. In Act II, Scene V, we as an audience are aware that Shylock's daughter and her beloved, Launcelot, are planning to elope. Shylock, of course, is completely unaware of this, even though Launcelot almost slips up and reveals the plan. The irony is that Shylock is obsessed with Jessica keeping his possessions under lock and key while he is gone, not realizing he is about to lose what to him is his chief possession, Jessica herself—and to a Christian man at that. This helps develop Shylock as a character so focused on minutia he fails to see the bigger picture. It also shows Jessica as more than a possession. She is a person who thinks for herself.
As noted above, the supreme incidence of dramatic irony occurs in this gender-bending play in Act IV, Scene I when Portia disguises herself as a male, so she can act as the lawyer defending Antonio against Shylock, and disguises her maid Nerissa as her male clerk. The audience knows what is going on, but the male characters in the play don't recognize the women. This scene develops Portia as a strong and creative person and counters her dead father's attempt to keep her as a damsel helplessly tied to a marriage fate which is out of her control.
Finally, we as an audience know that it is Portia and Nerissa who demand the rings their beloved men promised never to give up. There's dark comedy in this dramatic irony as we experience the men's anguish. They feel compelled to break their promises, and later more dramatic irony occurs as the women pretend to distress and astonishment that the rings are missing. This episode reinforces that we are all flawed humans and that forgiveness of a broken promise is more important than the letter of the law.