I just read the part where Philip joins the marines, and the theme of entrapment really popped at this point. Of course, Charley Kinraid was pressed--that one is obvious. Sylvia was trapped into marrying Philip (i.e., he didn't tell her that Charley was pressed and he made himself indispensable to Sylvia and Bell Robson) and she definitely saw Philip's house in town as a prison. Philip knowingly allowed himself to be pledged to join the marines after Charley returned to Monkshaven and Sylvia discovered Philip's lie.
Here's a picture of modern Whitby, the town Gaskell used as a model for Monkshaven.
Charley was entrapped but rose within the ranks of the navy, perhaps finding a new identity in the chains he was forced to wear. Sylvia became a ghost within the confines of her entrapment. I wonder what Philip will do with the chains he willingly put on.
I wish Gaskell told more of Hester Rose's story. I find her a far more appealing heroine than Sylvia. I suppose I just can't forgive Sylvia for not wanting to learn to read and write.