Granted, there is nothing new about granting a class of people with life-or-death power over their families. Such is the original definition of patriarchy. In ancient Rome, for example, a great many political, economic, and religious powers resided in the male heads of tribes, clans, and households. Among these was the power to commit infanticide. If a newborn was deemed healthy and supportable by the paterfamilias, it was initiated into the family with the proper rites. If not, it was smothered or drowned.

In Rome infanticide was not considered murder, any more than abortion is considered murder by the majority of Americans today. But the Romans regarded infanticide as a very grave act, which is why it could be performed only by the paterfamilias. In the sense that our present abortion law vests the pregnant woman with the power to commit a similarly grave act, it's tempting to dub her the "materfamilias." But of course she is nothing of the kind. The stern powers of the paterfamilias were fused with stern duties, such as atoning for crimes committed by the members of his household. In the organic metaphor we've inherited from the Romans (by way of Christian views of natural law), the "members" and the "heads" of families and other social institutions are bound by ties so powerful that they can be severed only by a kind of amputation.

Since the seventeenth century this organic metaphor has been challenged by liberalism's depiction of social institutions not as organisms made up of consanguine parts but as contractual arrangements between consenting individuals. The feminists' complaint against liberalism is that it has never, despite its contractual ethos, stopped conceiving of the family as an organic institution. As the political philosopher Susan Moller Okin has put it, liberalism still takes a "prescriptive view of woman's nature and proper mode of life based on her role and functions in a patriarchal family structure." That is why the chief goal of feminists like Okin is to restructure the family as a totally contractual arrangement from which anyone, but especially any woman, may withdraw at will.

But is this goal morally defensible? There's a very good reason why liberalism has never stopped seeing the family as an organic institution. Beginning with John Locke, liberalism has understood that not all human ties are contractual—most notably the tie between a parent and a child. Locke distinguished between legitimate political power, which may extend to life and death because it derives from the consent of the governed, and parental power, which may extend only to preserving the life of the child, because it does not, and cannot, derive from the consent of the child.

This crucial distinction collapses every time pro-choice arguments flip-flop between the language of individual rights and that of nurturant femininity. Pro-choicers begin by asserting equal rights for women—a line of reasoning that challenges the organic basis of family relationships. But equal rights are not enough when it comes to abortion, a decision that must balance women's rights against those of others, such as fetuses and family members. So pro-choicers define women's rights as more than equal, on the grounds that female decision-making partakes of a special moral wisdom. But what is the source of that wisdom? Not women's character or achievement as individuals but their membership in a class whose nature it is to care for others—a definition of womanhood that is nothing if not organic.