Lifelong exclusivity asks for a guarantee nobody can honestly give

The argument

A second argument for this position concerns what the promise of lifelong fidelity actually demands. Proponents point out that the commitment is typically made young, under strong social expectation, and about a stretch of life neither partner can foresee. It asks a person to guarantee not only how they will behave but how they will feel across decades in which everything else about them is expected to change. On this view a promise of that scope is not a serious undertaking that can be straightforwardly kept or broken; it is an aspiration dressed as a contract, and treating its failure as an outrage mistakes the kind of thing it was. The argument is strengthened, proponents say, by how common the failure is. Behaviour that occurs across every culture, class and era, among people otherwise scrupulous about their obligations, is better explained as a predictable feature of long partnerships than as a widespread moral collapse. Desire is not chosen, and attraction outside a relationship arrives unbidden; what a person controls is how they handle it. On this reading the honest account is that human beings are imperfectly monogamous, and that an ethic insisting otherwise will be broken routinely, leaving its main practical effect to be shame rather than better conduct. Defenders of the position are careful about what follows. They do not argue that anything goes, but that the appropriate response to infidelity is proportionate rather than absolute: a difficulty in a relationship to be understood and worked through, like other serious disappointments between people who have promised each other a great deal. Condemnation treats a single episode as though it cancels everything else the relationship is made of. On this account adultery is not wrong in itself, because the standard it is said to fail was never a reasonable one to set.

Premises

Counter-arguments

Critics answer that difficulty is not an excuse, and that promises are valuable precisely because they bind people once keeping them becomes hard. Many obligations ask for conduct against strong inclination, and nobody concludes from the frequency of theft that property rules are unreasonable. They also reject the move from feeling to action: the promise governs what a person does rather than what they want, and acting on desire remains a choice. Some add that the argument cuts the other way, since if exclusivity is genuinely too much to ask, the honest course is to say so beforehand rather than to accept the promise and plead its difficulty afterwards.

Rejecting the premises

[Rejecting P1] Critics reply that the promise governs conduct rather than feeling, so the fact that desire is unchosen leaves the obligation untouched. [Rejecting P2] They argue that frequency shows only that a standard is demanding, as many obligations are, not that it is unreasonable. [Rejecting P3] They object that proportionate treatment is perfectly compatible with the act being wrong, so the conclusion does not follow. [Rejecting C] They conclude that if exclusivity really is too much to ask, the honest course is to decline the promise rather than to break it.