The epistolary novel had grown in prominence throughout the 18th century until it arrived at the pen of Choderlos de Laclos. Richardson's Clarissa in England and Rousseau's La Nouvelle Heloïse in France, both epistolary novels, had been extremely well received. Their themes of education, romance, and the definition of the female self were repeated in Laclos's own work, but with a twist.
Laclos learned from the error of Richardon and Rousseau's ways in that he did not create a novel written from a single perspective, and he did not use the letters of his Dangerous Liaisons solely to report events. The diary-like epistles of Clarissa and La Nouvelle Heloïse certainly kept the plot moving along, but they were extremely flat. There seemed to be no motivation behind these letters.
To combat this lack of depth, Laclos wrote a kind of drama in letters, where multiple personages vied and schemed with, and against, each other through what they wrote. It is the portrait of the end of an era: an extremely rarified society gasps its last breaths on the pages of Dangerous Liaisons. It is the most extreme kind of epistolary novel one can imagine, a novel that could not be written except in letters, and it seems the last possible book of its kind. Its plot and its characters so perfectly motivate its own form that the result is terrifying and seamless.
The situations in Dangerous Liaisons are arranged so that only letters can communicate them. It is not so much what the characters claim to have been doing in their letters, but how they make these claims, which furthers the plot. Each letter has a purpose: it must convey some desire on the part of one of the characters, since no one would bother writing if he or she did not want something. This is evident in each letter that, at the very least, has the desire to be read written into it.
The masters of letter-writing are Merteuil and Valmont, who are able to anticipate how a reader will respond to what is written, and so, are able to write into the letter an understanding of how the letter will be read. For example, letter XLVII written by Valmont while in bed with a courtesan, goes to Tourvel by way of Merteuil. We can imagine how Merteuil, who knows where it was composed, will notice sexual references that will pass right by the Présidente. The double entendre, where what is read ("heard") depends on who is reading, is a favorite ploy of these aristocratic writers: its exclusivity, its power to determine who will be able to read it, is somehow very pleasing to them. The idea of "the game" is also extremely important to the writers of Dangerous Liaisons. They must feel, first, that something is at stake, and second, that they are completing against each other. The psychology of Dangerous Liaisons is extremely realistic and extremely dense—revolutionary for the time. Games of sexual conquest and tests of mental dexterity must replace military conquest, since the aristocracy of the time no longer participated in the actual military
Another problem in understanding the novel is the conflict of words with "the thing itself." Why experience love when you can write about it? Why be physically close to someone else when you can be intimate with them in a letter? Peter Brooks, in "Words and 'the Thing'" notes that in many parts of the book, desire seems to be trapped in writing, especially for the Marquise de Merteuil and the Vicomte. So, does love exist in these pages beyond the word "love"? The first response is probably to deny that "love" is just another four-letter word, but the novel seems to be asking repeatedly whether this has not in fact always the case throughout the history of literature. Love is just a word, and the other words of the novel must rally around it to explain it and to define its place among them.
More than an act of speech, the letter is a tool, a weapon. The letter does not only record reality, it creates it. What is obscene and to some, horrifying and dangerous, is when there is no difference between the act of love and the act of writing about it.