Ellen, you're right of course that Isabella bears by far the most blame here, since she was the one who had actually pledged herself to James, and very willingly, too. However, that doesn't make the third person in the triangle blameless, especially since he knew from the start that there was someone else.

To Lynn: Yes, it's pretty obvious in retrospect that Captain Tilney was *not* looking for a wife when he took up with Isabella. I guess the big problem was that the two of them were playing two different games. Isabella was playing "for keeps" while Frederick was playing "for now", all the while knowing full well that his partner was (at least trying) to play by very different rules! :-(