When David H. Petraeus resigned as CIA director because of adultery, he was widely understood to be acknowledging a misdeed but not a crime. Yet in his state of residence, Virginia, as in 22 others, adultery remains a criminal act, a vestige of the way U.S. law has anchored legitimate sexual activity within marriage.
In most of those states, including New York, adultery is a misdemeanor. But in others -- Idaho, Massachusetts, Michigan, Oklahoma and Wisconsin -- it is a felony, though rarely prosecuted. In the armed forces, it can be punished severely although usually in combination with a greater wrongdoing.
This is yet another example of American exceptionalism: In nearly the entire rest of the industrialized world, adultery is not covered by the criminal code.
Like other state laws related to sex -- sodomy, fornication, rape -- adultery laws date to the Old Testament, onetime capital offenses stemming at least partly from a concern about male property. Peter Nicolas of the University of Washington Law School said the term stemmed from the notion of "adulterating" or polluting the bloodline of a family when a married woman had sex with someone other than her husband and ran the risk of having another man's child.
Linda C. McClain, who teaches family law at Boston University, likes to give her students two decisions from New Jersey courts, the first from 1838 and the second from 1992, to demonstrate how things have changed.
In the 1838 decision, the court said that the harm of adultery lay not in "the alienation of the wife's affections, and loss of comfort in her company," but in "its tendency to adulterate the issue of an innocent husband, and to turn the inheritance away from his own blood, to that of a stranger."
In the 1992 ruling, in a civil case, the court said that "adultery exists when one spouse rejects the other by entering into a personal intimate sexual relationship with any other person." It said it was "the rejection of the spouse coupled with out-of-marriage intimacy that constitutes adultery."
Most states have purged their codes of laws regulating cohabitation, homosexual sodomy and fornication -- sex between unmarried adults -- especially after the 2003 Supreme Court decision of Lawrence v. Texas that made sexual activity by consenting adults in private legal across the country. But the question of how that ruling affects adultery remains unanswered because others may be harmed by adultery -- a spouse and children. Several courts have alluded to the constitutionality of adultery laws since the Lawrence decision.
But Melissa Murray, a professor of law at the University of California, Berkeley, said she thought "most courts in light of Lawrence are going to give adultery a wide berth."