Constitutional law has long assumed that mothers and fathers are fundamentally different. Maternity, that law posits, is certain, obvious, and monolithic - consolidated in an easily identifiable person who is at once a biological, social, and legal parent. Paternity, in contrast, is construed as uncertain, nonobvious, relative, and often unclear. Over time, constitutional law has grown more insistent about the obviousness of motherhood. It also has cemented its idea of maternity into a fundamental principle of sex equality law that applies in settings - like transgender rights - that have nothing to do with certain mothers and uncertain fathers. Constitutional law's logic of maternal certainty and paternal uncertainty invites criticism for many reasons. It channels the notion that pregnant women are presumptive mothers. It perpetuates questionable stereotypes about mothers and fathers. It determines who can be a parent and how he, she, or they ought to parent. It is in serious tension with constitutional law's disestablishment idea. For all of these reasons, constitutional maternity warrants reform, and one promising pathway of reform is family law's less regressive and more multidimensional vision of motherhood. Never as uncomplicated as the Supreme Court has assumed, maternity has become considerably more complex in light of the new forms of kinship enabled by alternative reproduction and its legal accommodation. During the exact time that the Supreme Court has insisted that women and men are inherently different because of maternal certainty and paternal uncertainty, state family law has painted a more complicated picture. Maternity, that picture suggests, often is uncertain and nonobvious. It often is relative. Like paternity, it often is a matter of opinion - judicial opinion. Most remarkably, state family law has shown that maternity is all of these things by relying on the same body of federal constitutional doctrine that insists that mothers and fathers are fundamentally different - and fundamentally different because mothers, unlike fathers, are basic, singular, and monolithic. This Article argues that progressive advances surrounding the new maternity ought to unsettle regressive tendencies surrounding constitutional maternity. These regressive tendencies touch and burden many: from unmarried fathers and transgender individuals to nonbiological and biological mothers. This Article imagines what the new maternity emerging from family law would mean for constitutional law. The idea that the new maternity could unsettle constitutional maternity is not necessarily radical - that project has been unfolding in state courts for years. The consolidation of the new maternity in constitutional law, however, could have meaningful consequences both within and beyond the law of parenthood, destabilizing everything from parentage regimes that rest on the notion of essential biological difference to the argument that transgender discrimination is not illegal because "sex" is not "a stereotype."
