The primary significance of windows in Madame Bovary is to symbolize escapism. This is shown in many ways.
In chapter 7, her life is described as follows:
. . . for her, life was as cold as an attic with a window looking to the north . . .
This indicates that most of the time, Madame Bovary aspires to do or see something else newer, or better. The saying "the grass always looks greener on the other side" is applicable to Emma. She is never satisfied and, as such, she always looks at some other dream into which she can invest her attention.
In chapter 17 (part II, chapter 8), we find Emma fantasizing about the three most influential men in her life, aside from her father: the Vicomte, Leon, and Rodolphe. Here, the window is tantamount to a screen where she can project her fantasies.
She fancied she saw him opposite at his windows; then all grew confused; clouds gathered; it seemed to her that she was again turning in the waltz . . . on the arm of the Viscount, and that Leon was not far...
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