Given the following extract from The Merchant of Venice, Act III, sc. 2:
Portia is shown to be the type of character whose voice will not be denied. Shakespeare shows this in different settings. When she is forced to live with the choices of the suitors and the caskets in terms of her marriage, Portia says, "so is the will of a living daughter curbed by the will of a dead father." In saying this, Portia shows that her will is not going to be checked or limited. When she dons the persona of Balthazar, she affirms "the quality of mercy" to challenge both the legal structure and Shylock's claims to it. At the same time, she challenges Shlyock's premise in exacting "a pound of flesh." In these situations, Portia is shown to possess an irrepressible voice that forces individuals to see what can be as opposed to what is. Shakespeare gives us a maiden who has both "tongue" and "thought" to go with it.
When Portia speaks to Bassanio before he leaves in Act III, scene 2, she is making a direct statement to the social condition that silences girls like her. Portia wants to tell Bassanio the truth as to which casket he should choose in order for them to be together. However, she is unable to give him the direct answer because of the oath to which she is "foresworn" and the condition in which girls are not able to use their voice. It is this condition that she critiques in the line "And yet a maiden hath no tongue, but thought." Portia is unable to speak, and this is where she has "no tongue." She is unable to speak because of social convention that precludes her being able to make her own choice for suitor, a reality that was forged "by the will of a dead father." As a maiden, she has "no tongue" because of these conditions that preclude her from activating her voice. However, it is clear that she has plenty of thoughts, as she speaks to Bassanio from both heart and mind.
Portia's words reflect both her feelings towards him ("One half of me is yours, the other half yours-"), and also a level of thought because in talking to him in such a way, she has in fact been able to delay his departure in leaving. In this way, Portia defies the social convention and even emotional convention that precludes her voice. It is her way of rejecting a world in which a women like her is told to "hath no tongue." Portia challenges this condition with her words and the thought raging beneath it. She claims a world in which a maiden "hath no tongue, but thought." However, it becomes readily evident that she possesses both and is unafraid of who recognizes it.