As Catherine finds her way through the perils of navigating Bath, she begins to figure out who she can trust and who she cannot, and to have some confidence in her own judgments of people. (As a side note, she reminds me a bit of Fanny Price as she gains enough confidence to take a stand against the Thorpes and holds her ground based on her own convictions). As she becomes more skeptical of the Thorpes, she relies more heavily on Henry's education and judgment. I love how she's guided by him and, even if she's not sure she understands him (such as in their conversation about Captain Tilney and Isabella in Ch. 19), she has enough confidence in his goodness to trust him. I think it's all summed up in her deciding that, "Henry Tilney must know best." :-)