 On the contractual account, not just any contracts count as marriages. The default content of marital promises is supplied by social and legal practice: sexual exclusivity, staying married, and so on. But it entails that spouses may release one another from these moral obligations. For example, extra-marital sex has often been construed as morally wrong by virtue of promise-breaking: if spouses promise sexual exclusivity, extra-marital sex breaks a promise and is thereby prima facie wrong. However, if marital obligations are simply promises between the spouses, then the parties can release one another, making consensual extra-marital sex permissible (Wasserstrom 1974). Marriage is also sometimes taken to involve a promise to stay married. This seems to make unilateral divorce morally problematic, as promisors cannot release themselves from promissory obligations (Morse 2006). But standard conditions for overriding promissory obligations, such as conflict with more stringent moral duties, inability to perform, or default by the other party to a reciprocal promise would permit at least some unilateral divorces (Houlgate 2005, Chapter 12). Some theorists of marriage have suggested that marital promises are conditional on enduring love or fulfilling sex (Marquis 2005, Moller 2003). But this assumption is at odds with the normal assumption that promissory conditions are to be stated explicitly.