But today, as an increasing number of women can provide for themselves, the use of sex in exchange for favours seems less and less acceptable. However, the phenomenon continues and manipulation, even when exercised subconsciously, is still a strategy used by some women. "They are probably as numerous as those who faked orgasm at one point or another in their life," suggests Saulnier.

The attitude apparently comes from the way we were raised, by our family and by society. Whether they come from a blue-collar or white-collar homes, all women learn subtle messages during childhood. Were you never told, 'the way to a man's heart is through his stomach'?

"There is a subliminal message there," Saulnier says. "Of course, the stomach is associated with food, but the part below the stomach is also implied in the expression. Some women will even say that if you want peace in your relationship, give sex to your man! It's not surprising, then, that this behaviour is transmitted from one generation to the next."

Religion also contributed to promoting what is considered "legal prostitution." The man had to provide for his wife and his wife had to submit to the conjugal duty. Admittedly, here, sexual bartering was the norm.

A host of reasons

Just like Sylvia, who admits she has had sex so that her boyfriend won't be cranky, Martha also weighs in the debate. "Last year, there was a night where Paul was furious at me. He was convinced that I contradicted him in front of his brother on purpose. But I was only expressing my disagreement on a very specific point. Since I was sure that there was no point in trying to discuss this with him, I decided to put an end to the fight in bed!"

Frank Hajcak and Patricia Garwood, authors of Hidden Bedroom Partners, believe that using sex to fix wrongs has two negative consequences. "First, neither partner gets much pleasure from it. The person who tries to calm down the other sees sex as a task, while the unhappy spouse takes it for granted. Secondly, it keeps both partners from growing emotionally. One plays the role of a wet-nurse for the infantile partner. Neither person learns to take responsibility for his or her actions."