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[Colonel Fitzwilliam:] "[…] But in matters of greater weight, I may suffer from want of money. Younger sons cannot marry where they like."
[Elizabeth:] "Unless where they like women of fortune, which I think they very often do."
"Our habits of expense make us too dependent, and there are not many in my rank of life who can afford to marry without some attention to money."
"Is this," thought Elizabeth, "meant for me?" and she coloured at the idea; but, recovering herself, said in a lively tone, "And pray, what is the usual price of an earl's younger son? Unless the elder brother is very sickly, I suppose you would not ask above fifty thousand pounds." (33.12-15)
Here, Colonel Fitzwilliam slips Lizzy a little hint that, while he thinks she's cute and all, he's not about to marry her. He may be the son of an earl, but he's the younger son, which means he's not going to inherit the estate—unless his older brother dies. Lizzy recovers by making a joke about how much it costs to marry an earl's younger son (i.e., how much money does the girl have to bring to the marriage?) but Fitzwilliam is serious: he has to marry a rich woman to support him in the manner to which he's become accustomed—his "habits of expense." He's our clue that, while this system of marriage isn't great for women, it's not great for men, either.