Middlemarch is built on a foundation of bad marriages. There are those which happened in the past, which drove Julia and Bulstrode into hiding. There are those in the present, such as Dorothea’s marriage to Casaubon and Lydgate’s to Rosamond, in which the marriage is not built on a thorough understanding of each other, but on an idealized version of the respective characters.

Premarital idealization is often associated with social mobility, as in the cases of Casaubon and Rosamond. Casaubon marries Dorothea because marriage is expected of a man in his position, while Rosamond marries Lydgate because she wants to attach herself to a man who is moving up in the world. Meanwhile, Dorothea and Lydgate fall in love due to more idealistic and romantic reasons. They love the idea of love, rather than their actual partner. Dorothea convinces herself that Casaubon is a great intellectual whom she can help achieve greatness. She wants to achieve her ambitions vicariously through her husband, which (in a patriarchal society) necessitates marrying a great man. Thus, she idealizes Casaubon and turns him into something he is not. Lydgate similarly misunderstands Rosamond. He sees only her beauty, rather than her cynical ploy for social mobility.