In the 1950s, using the marriage license as a shorthand way to distribute benefits and legal privileges made some sense because almost all adults were married. Cohabitation and single parenthood by choice were very rare.

Today, however, possession of a marriage license tells us little about people’s interpersonal responsibilities. Half of all Americans aged 25 to 29 are unmarried, and many of them already have incurred obligations as partners, parents or both. Almost 40 percent of America’s children are born to unmarried parents. Meanwhile, many legally married people are in remarriages where their obligations are spread among several households.

Using the existence of a marriage license to determine when the state should protect interpersonal relationships is increasingly impractical. Society has already recognized this when it comes to children, who can no longer be denied inheritance rights, parental support or legal standing because their parents are not married.

As Nancy Polikoff, an American University law professor, argues, the marriage license no longer draws reasonable dividing lines regarding which adult obligations and rights merit state protection. A woman married to a man for just nine months gets Social Security survivor’s benefits when he dies. But a woman living for 19 years with a man to whom she isn’t married is left without government support, even if her presence helped him hold down a full-time job and pay Social Security taxes. A newly married wife or husband can take leave from work to care for a spouse, or sue for a partner’s wrongful death. But unmarried couples typically cannot, no matter how long they have pooled their resources and how faithfully they have kept their commitments.

Possession of a marriage license is no longer the chief determinant of which obligations a couple must keep, either to their children or to each other. But it still determines which obligations a couple can keep — who gets hospital visitation rights, family leave, health care and survivor’s benefits. This may serve the purpose of some moralists. But it doesn’t serve the public interest of helping individuals meet their care-giving commitments.

Perhaps it’s time to revert to a much older marital tradition. Let churches decide which marriages they deem “licit.” But let couples — gay or straight — decide if they want the legal protections and obligations of a committed relationship.