 On this approach, the structure of marriage derives from the behavior needed to maintain such a relationship. Thus marriage involves a commitment to act for the relationship as well as to exclude incompatible options—although there is controversy over what specific policies these general commitments entail. To take an uncontroversial example, marriage creates obligations to perform acts which sustain love, such as focusing on the beloved’s good qualities (Landau 2004). More controversially, some philosophers argue that sustaining a love relationship requires sexual exclusivity. The thought is that sexual activity generates intimacy and affection, and that objects of affection and intimacy will likely come into competition, threatening the marital relationship. Another version focuses on the emotional harm, and consequent damage to the relationship, caused by sexual jealousy. Thus, due to the psychological conditions required to maintain romantic love, marriage, as a love-protecting institution, generates obligations to sexual exclusivity (Martin 1993, Martin 1994, Scruton 1986, Chapter 11, 356–361, Steinbock 1986). However, philosophers dispute the psychological conditions needed to maintain romantic love. Some argue that casual extra-marital sex need not create competing relationships or trigger jealousy (Halwani 2003, 235; Wasserstrom 1974). Indeed, some have even argued that extra-marital sex, or greater social tolerance thereof, could strengthen otherwise difficult marriages (Russell 1929, Chapter 16), and some polyamorists (those who engage in multiple sex or love relationships) claim that polyamory allows greater honesty and openness than exclusivity (Emens 2004). Other philosophers have treated sexual fidelity as something of a red herring, shifting focus to other qualities of an ideal relationship such as attentiveness, warmth, and honesty, or a commitment to justice in the relationship (Martin 1993, Kleingeld 1998).