Marriage is no longer the only, or even the chief, place where people make most of their major personal, occupational, residential and financial decisions, or where they incur obligations to others. More than a third of women who give birth in any given year are now unmarried. And at the other end of the age spectrum, older adults are the fastest growing group of cohabitors in the country.

This is a game-changer, both for our emotional lives and our social policies. As a society, we can no longer act as though married couples are the only people who need support for their caregiving obligations, from employer-provided healthcare for dependents to legal recognition of their interdependencies.