In 2007, researchers from the University of Texas categorized 237 motivations for humans to have sex. Recently, researchers at the University of Toronto divided the most common into two broad categories: approach motives pursue a positive outcome, like increasing intimacy; avoidance motives aim to avoid conflict or guilt. The Canadian team found that adding the fairly un-sexy drives of duty, resignation and guilt which significantly affect the health of a relationship, and could spell the difference between a happy marriage and a rocky one. Elizabeth Bernstein is a columnist for the Wall Street Journal, where she wrote about the studies published by University of Toronto in October.