Daisy Miller: Theme Analysis

Free Will versus Traditional Morality
Much of the story focuses on the choices that characters make under moral pressure. The book begins with the decision that Winterbourne makes to approach Daisy despite the moral code that renders such an approach impolite. Because Daisy does not take offense at his approach, which normally a young woman would have done immediately, Winterbourne continues to flaunt the moral code he knows so well. He eventually commits the socially unacceptable act (unacceptable at least to Mrs. Costello) of taking Daisy to the castle alone, after knowing her for only a few days.
For Winterbourne, there are no consequences for this behavior, and his life continues much as it had before. For Daisy, however, this behavior ruins her reputation with Mrs. Costello, who might have used this prior knowledge of her character to become the expert on Daisy that people regard her as at the end of the book. Mrs. Costello and Mrs. Walker represent the traditional morality that abhors Daisy's behavior. Under this version of morality, women should avoid conduct that appears to be showing romantic interest in someone that they don't intend to marry. This applies to Daisy's relationship with Giovanelli. Because of his questionable social position, and because Daisy has behaved this way with other men, it is assumed that Daisy doesn't intend to marry Giovanelli. Instead, it seems, she is merely having a love affair, and the references at the end of the book to the cab-driver and servants at the hotel talking about Daisy and making jokes imply lewd behavior. In other words, the "common" people are making jokes about Daisy having sex with Giovanelli in the Colosseum. Winterbourne seems to make this judgment as well.
Daisy, on the other hand, seems to believe that she has the freedom to choose. She believes that she can take Giovanelli to see the Colosseum at night, and that such a decision implies no further consequences. What the story shows, however, is that people will make judgments about such behavior, and will assume that Daisy went to the Colosseum with the clear intention of behaving inappropriately, even if she had no intention of doing so. In other words, people will make their judgments regardless of Daisy's actual intentions. If consequences are always unequivocally negative when a woman makes a choice like this, and if the consequences of social judgment matter, as they do for a young woman who might be looking for a husband and who circulates among polite society, then the exercise of free will becomes a dangerous quality. A woman with "free will" becomes someone who acts in ways that can be misread.
The story seems to suggest, then, that Daisy's intentions don't really matter. It doesn't matter, in the end, if she is completely innocent and if the relationship between her and Giovanelli was entirely platonic. She is ostracized for the appearance of her behavior, not the reality. It doesn't matter what she actually does with Giovanelli, only what she might or could be doing with him.
The consequences of certain behaviors are very different for the men in the story. Winterbourne can choose to associate with Daisy, and he can choose to take her to the castle. Likewise, Giovanelli can freely associate with Daisy. The only possible consequence for him is that she will eventually become socially ostracized and thus an encumbrance to him rather than a means of acquiring greater social access.
To oversimplify a little, the story suggests that freedom is something that men can enjoy, but that it is fatal (literally, in Daisy's case) to women. Women are expected to be the source and guardian of moral virtue, but men cannot be expected to adhere to the same standards. In the sphere of relationships between the sexes and sexual morality, a double standard operates.