Old ladies must never be crossed: in their hands lie the reputations of the young ones.
[Il ne faut pas fâcher les veilles femmes; ce sont elles qui font la réputation des jeunes.]
Letter Fifty-one, from the Marquise de Merteuil to the Vicomte de Valmont, contains the Marquise's latest strategies for the seduction of Cécile and the Présidente de Tourvel. Here she is describing an incident in which she accidentally offended a group of old ladies and subsequently had to spend a good deal of time complimenting them to prevent them from ruining her reputation with gossip.
This quotation touches on the theme of education in Dangerous Liaisons. Here, education does not take place in schools; rather it occurs in drawing rooms and at the opera. An older, experienced woman takes a younger woman in hand and introduces her to society. The older woman's particular place in society assures the younger woman a place. An older woman can teach a younger woman to be independent, to live on a good reputation and a good fortune without a husband. Essentially, an older woman can teach a younger woman how to live in society while, at the same time, breaking all of society's stated rules.