How we cite our quotes: (Part.Letter.Paragraph)
Quote #4
As a matter of fact, I was thinking, when he was announced, of how best to throw him into despair. (1.10.4)
This seems to be one of Madame de Merteuil's guiding principles. She's a sower of discord and despair. It's what she lives for and what brings her the most pleasure. It's one of her personal rules, a lens through which she sees the world: how can I make this person miserable?
Quote #5
How often we have been encouraged to cultivate a good heart! Yet we are forbidden to follow its dictates where a man is in question. (1.16.2)
Cécile's heart is telling her to be kind to Danceny and answer his letters, but her moral principles about how she's supposed to behave with men are telling her otherwise. She's experiencing a lot of conflict about it, like we always do when our heart tells us one thing and our head something different.
Quote #6
But tolerance I see as no more than dangerous frailty when it brings us to look with equal favour upon virtue and vice. (1.32.1)
This is a good example of how principles can't always be absolute. Madame de Volanges wants to be a tolerant person, but she doesn't think that tolerating wickedness is acceptable. Unlike Valmont and Merteuil, she wants her principles to guide virtuous behavior, as opposed to just being expedient.