The UK and US should take the lead in recognising the limits of law in policing infidelity.

At the state funeral of former French president Francois Mitterrand, his long-time mistress Ann Pingeot appeared alongside his wife and their two sons. Meanwhile, in many Islamic countries women can be stoned for adultery.

As those examples suggest, attitudes toward infidelity vary widely and provide a window into global norms concerning extramarital sex and the law’s role in policing it.

Among developed societies, the percentage of married people who admit to having been unfaithful over the previous year ranges between 2% and 25%. The US and the UK are at the lower end of that range, somewhere between 2% and 4%. Public disapproval, though, is relatively high. The percentage of adults who say that extramarital sex is morally unacceptable is 84% in the US and 76% in the UK.

In the US, the law backs up that disapproval. Twenty-one states still have misdemeanor or felony prohibitions on adultery. Adultery also figures as a basis for job terminations, sanctions or demotions, particularly in the military, and as a factor in allocating property and custody in divorce cases. In the UK, adultery is not a crime but it is a ground for divorce.

In other societies, the penalties are far more substantial. Stoning as punishment for the crime can occur legally or illegally in at least 15 countries. Flogging is also an option in many states. The double standard in enforcement is pervasive in some nations. In some Islamic countries only women have been convicted of adultery and sentenced to death by stoning. And because some of these nations do not recognise coercion as a defence to rape, married women who have been sexually assaulted can be guilty of adultery.

Reform in many nations is long overdue. In western societies like the US, enforcement of criminal prohibitions has been infrequent, intrusive, idiosyncratic and ineffectual. It should be abolished.

In employment cases, courts should not permit dismissals based on private sexual conduct in the absence of some demonstrated impairment of job performance. Nor should courts allow infidelity to influence alimony and custody awards.  

None of these reforms should be seen as diminishing societal respect for marriage as an institution. Rather, they simply recognise the limits of law in policing fidelity, and the excessive costs of attempting to do so. The widespread public ignorance about such prohibitions was well illustrated in the US when New York governor David Paterson acknowledged at a news conference that that he had had several extramarital relationships but ‘didn’t break the law’.

The New York Times followed up with a report that began, ‘Well, actually….’. Adultery is a misdemeanor in New York, punishable by a fine of $500 or 90 days in jail. That needs to change.

Change is also necessary in laws and practices that target military officers and politicians for conduct that is widespread. In the US, the costs of over-enforcement were well illustrated by the forced resignation of David Petraeus, the Director of the Central Intelligence Agency and one of the nation’s most decorated four-star generals. Although, as Petraeus acknowledged, his affair with his biographer showed ‘poor judgement’  and was ‘unacceptable as a husband and a leader’, it had nothing to do with his job performance.  

The international community, too, needs to take a stronger stance in condemning adultery prosecutions as human rights violations. Sustained pressure from broad coalitions of nations as well as prominent non-governmental organisations could help to reform laws and social practices that impose a sexual double standard and barbaric punishments.

Countries like the US and UK could take a leadership role, but only if their own legal policies do not embody outmoded and ineffectual responses to adultery.

Deborah Rhode is McFarland Professor of Law at Stanford University and author of ‘Adultery: infidelity and the law’ (Harvard University Press, 2016)