Towards the end of Wide Sargasso Sea, Antoinette 'goes mad'--but, what exactly is the operational definition of madness that we are using? In class discussions, we were saying that madness is determined by how your society sees you. But, the problem with this definition is the fact that towards the end of the novel, Antoinette goes to England, where she is no longer being viewed by her society. The only people in England who have any contact with her, besides Rochester, have no idea what the world that she comes from is like, so it makes sense that they would see her as being mad.
When Rochester first comes to where Antoinette lives, he is seen as an outsider and people don't really know how to understand him. This is similar to how Rochester, and everyone else in England, don't understand Antoinette. But, a difference arises because Rochester isn't considered to be 'mad'; this seems to be because everyone already knew that Antoinette's mother was mad, and it was a ready-made excuse for Rochester to use to explain his wife's behavior.
I think that the solitary confinement that Antoinette faces in part three of the novel definitely drives her mad. But, I think that her madness is very different from what Rochester thinks that it is. Rochester locks her up because he thinks that she is totally incapable of making rational decisions and functioning in society, but she isn't ever really given the chance to be a part of England's society. And, I think that she is able to make rational decisions--when she attacks Mr. Mason, this may seem like a totally irrational thing to do, but not when you think about her reasons for attacking him.
Antoinette's suicide is another example of how she is still able to make rational choices. While suicide may seem like an irrational thing to do, one has to look at what her options are; she can remain confined in an attic for the rest of her life, or she could not. I think that staying in the attic would have been better proof that she was mad than any of the reasons that Rochester used to justify keeping her there. When Antoinette chooses to jump out of the window, she is freeing herself from the life of a madwoman that she had been forced into. However, by jumping she cements the idea that she is crazy in the minds of readers (and, as seen in Jane Eyre, the other characters in the story). I'm a little hesitant to say that she's in a Catch-22, but she definitely is stuck in a situation where she can't win. She is forced to choose between life and freedom, and by jumping out of the window, she chooses freedom--from both her husband and the identity of a madwoman that he has forced on her.