Irony of appeal
After a disastrous encounter with Valmont, Cécile writes to the Marquise begging for help, or at least advice. She does not know that the Marquise is the one who engineered Valmont's attack on her. This is an example of dramatic irony, when the reader knows something the character does not.
Irony of deception
At Valmont's urging, Cécile steals the key to her bedroom and gives it to Valmont, believing that he will help to pass letters back and forth between Cécile and Danceny. In reality, Valmont intends to sneak into Cécile's room and "seduce" her himself. After the rape, because Cécile was the one who stole the keys she believes herself wholly responsible for what happened.
Irony of virtue
In most conventional morality plays, vice is punished and virtue is rewarded. Both the young characters, Danceny and Cécile, come from religious backgrounds. Danceny is a Knight of Malta and Cécile was raised in a convent. They are both used by the older and more cynical characters, and both lose their innocence and their virginity but not with each other. Although they love one another, their virtue is not rewarded and each enters a self-imposed exile. Danceny returns to his religious order and Cécile returns to the convent to become a nun. Likewise, when the virtuous Mme. de Tourvel yields to Valmont's trickery and sleeps with him she is overcome with remorse, sickens, and dies.
Although the truly vicious people in the story are punished (the Marquise with disfigurement and Valmont with death), the virtuous ones are not rewarded. Instead, their goodness leads them to be used and exploited by others.
Irony of love
Valmont, an amoral pleasure-seeker who would in modern times be considered a serial rapist, is undone by something he frequently exploits in others: love. He falls in love with the married Mme. de Tourvel, a victim to his own weapon of choice.
Irony of enabling
The elderly Madame de Rosemonde, who is Valmont's aunt, is a kindly person who wants for good things to happen. Ironically, it is her home where all the debauchery occurs. Despite her good intentions, she ends up enabling Valmont to seduce both the innocent Cécile and her good friend Madame de Tourvel. She herself is under no illusions about Valmont but still permits him to occupy space in her home and to have unsupervised access to prospective victims.
