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.