In my opinion, accepting this explanation would destroy the dramatic integrity of the play. For one thing, to make the logic of the story depend this sort of explanation is to basically invent a new play which is a substitute for the one that is written down. And if one of the play's leading characters, in the play's climactic scene, is functioning as a mere spokesperson, speaking the words of a character who never even appears, then the whole play becomes meaningless and certainly Portia's role in the courtroom becomes completely meaningless. To have the crucial arguments delivered by the Duke or by some true legal expert would mean that the crucial plot point in the whole play would essentially come from a deus ex machine, and in this case, the story would somehow lose its point.
For the same reason, I think it's important that the audience recognize from the very first moment that this supposed distinguished doctor of law is in fact Portia. If we don't see through Portia's disguise, then in Act 4 Antonio's saviour is still a deus ex machine, and the play loses its power, and it's too late to say in Act 5, "Oh, it was really Portia." Moreover, we need to be able to recognize Portia while she gives ‘The quality of Mercy’ speech because for me this is the defining moment in the play for Portia. It is the moment when we realize that she is noble and courageous (and much more intelligent than anyone else in the courtroom). Portia’s rhetorical shift involves removing “mercy” from the realm of legal compulsion, and thus sidestepping his question. By allying “mercy” with “heaven”, “God” and “kings”, Portia takes it from the created law and makes it part of the metaphysical system which surrounded Renaissance ideology. She no longer has to argue over right and wrong in this individual case (“the justice of your case”), but claims to be dealing with issues of Right and Wrong on a larger scale, even Good and Evil.
Read more at Suite101: The Quality of Mercy: Portia's Oration in The Merchant of Venice http://www.suite101.com/content/the-quality-of-mercy-a30269#ixzz15YovCOL7 Portia loses her whole impact in the play if we don't see who she is while she's giving this speech, and she surprises us, as we'd taken Portia for a bit of an dismissive and ignorant woman as is shown when she is mocking her suitors with Nerissa – ‘How oddly he is suited!’, whereas now we suddenly realize how intelligent she is. More intelligent than she realizes herself, I believe.
Although Portia herself is almost a deus ex machina in the courtroom, since she has not been involved in the Shylock plot at all [previously, and we have had no previous reason to even suspect that she had any legal expertise (which to me does seem like a genuine flaw in the plot), I think that there is no other character available who could present the winning arguments in the courtroom in the same way. If Antonio or any of the other characters is capable of coming up with the arguments Portia uses, then fundamentally this says that Shylock simply underestimated his opponents and is not a worthy antagonist.
As it is, at the end of the play, Antonio and Bassanio remain the heroes of the play. Antonio had been within a few moments of losing his life, and Portia pulled off an incredible feat of legal intelligence to save him, and now they're all back in Belmont and, astonishingly enough, after having seen Portia's true abilities in the Duke's chambers in Venice, now in Act 5 Antonio and Bassanio and the audience go back to treating her as just another trivial dame. The trick with the rings is what brings the play back down from near tragedy to comedy. Portia, a woman, has managed to save Antonio's life by outsmarting an opponent that he himself was not able to get the better of which would have delighted the audience.
If we believe in Act 1 that Portia is a shallow airhead who is cruel to her suitors, a spoiled little rich girl, then you cannot believe her trustworthy in the courtroom. Her speech ‘You see me Bassanio’ begins with an affective paradox. She presents herself to Bassanio using the first person in an engagingly personal manner – ‘Such as I am’. The speech shifts from personal commitment to a more formal bond marked by the giving of her ring, and is signalled by the change to third person (‘an unlessoned girl… she’). Even when she escapes her father’s will through Bassanio’s choice of the lead casket, she subjects herself immediately to her husband’s authority – ‘This house, these servants, and this same myself / Are yours, my lord’s.’ Ultimately, during the courtroom scene and ring scene she establishes control over her husband, and it is in the ring scene where Portia’s mocking and cunning character is shown again - ‘For by this ring the doctor lay with me’, she wraps Bassanio around her finger, taking control over him despite her inferiority as a woman.
I believe that Portia is like most people in the real world, in that she's capable of being flippant and caustic and even cruel in a lot of circumstances, but that doesn't mean she's not capable of serious thought when it's needed. The one thing we see for sure from her comments in Act 1 is that she is definitely intelligent (or, at the very least, clever). And the fact that Portia surprises us in the courtroom scene and shows an unexpected depth is, in my opinion, part of what would have made the play comic. If the previous acts had shown Portia as wise and super-competent, then as I see it, the courtroom scene wouldn’t have worked. In this case, watching Portia defeat Shylock would have been almost an unfair fight.
Portia, like so many women, appears to be the victim of the belief that it's not a good thing for women to be intelligent. She downplays her intelligence at the start of the play, hidden it even from herself, allowed herself to express it only in socially acceptable forms, such as sarcastic banter. Her destiny is even controlled by her dead father, still a victim of her father’s patriarchal authority and control. When there is the moment when she really needs that intelligence, and she has the right to use it because she is disguised as a man. To be acceptable to an Elizabethan audience, and even to a modern one, you need the comedy to disguise the feminism, which I believe is what Shakespeare was trying to do in his portrayal of Portia.
