I also agree that comparing the characters of Miss Tilney and Miss Thorpe gives great insight into both characters - I know I began to feel even more strongly all of the good qualities Isabella is missing once Miss Thorpe entered the scene.

I believe the contrast between the sisters of the two gentlemen in Catherine's life is every bit as important as the contrast between Mr. Tilney and Mr. Thorpe themselves. Through our knowledge of the ladies, we get a even better idea of what home life might be like for Catherine depending on which man she might marry - becoming more intimate with the Thorpes seems only to lead to degredation of character and shallowness, while knowing the Tilney's better would expose Catherine lively, cultivated minds that would help her to be a better person. This would seem especially important in Catherine's case since she is so young, and there is still a lot of "flexibility" in her character - she seems still capable of learning and growing. I would much rather see Catherine become more like Miss Tilney than Isabella. I could not help but cheer my approval of our heroine's decision to behave honorably to the Tilney's in spite of pressure from her brother and "friends".