Adultery is older than law.
It has outlived empires, outlasted kings, defied religion, and shaped the whispered heartbreaks of every century. But what happens when we set aside morality and look at it through the quiet, sharp lens of economics?
We see something different.
We see a breach of contract.
We see a failed investment.
Marriage, as economists remind us, is not just a romantic bond—it is a joint venture. A partnership built on long-term, specific commitments: shared income, shared parenting, shared futures. When one partner steps outside that agreement—not just emotionally, but physically—they’re not just breaking hearts. They’re breaking terms.
So what does adultery cost?
That’s not a moral question. It’s an economic one. Because the injured party in a marriage often made sacrifices in good faith: career paths paused, earnings forfeited, years invested in domestic or emotional labor. Adultery, especially when it ends the marriage, renders those investments partially or wholly unrecoverable.
In this framing, adultery is an externality—a cost imposed by one party on another without compensation. And like any externality in economics, it raises a central question:
Should the law step in to correct the imbalance?
Historically, many legal systems said yes.
Fault-based divorce regimes treated adultery as grounds for punishment. Some offered compensation. Some affected alimony and custody decisions. In these systems, the unfaithful party bore the legal consequence of their breach—restoring a kind of economic balance to the betrayed spouse.
But then came no-fault divorce.
The shift was seismic. Adultery, once central, became legally irrelevant in many jurisdictions. Now, marriage could end simply because it no longer “worked.” Blame became unspoken. Courtrooms turned away from motive and focused instead on division.
And with that, adultery was decriminalized—not in code alone, but in consequence.
The economic result? The cost of infidelity shifted—from the betrayer to the betrayed.
If a faithful spouse had made deep investments in the relationship, expecting long-term returns—and the marriage suddenly collapsed due to infidelity—the law no longer recognized the asymmetry. Each walked away with “equal” rights, but not with equal losses.
This, the economic approach argues, is inefficient.
Because it undermines trust in the marital contract.
And when trust falls, so do incentives to commit deeply, to specialize in the household, to invest in shared futures.
So what might a better system look like?
Not one of puritanical punishment—but one of contractual accountability.
A regime where couples could choose to include adultery clauses in their prenuptial agreements.
Where courts could consider infidelity in asset division—not out of morality, but equity.
Where the law reflects that betrayal, when it dissolves a partnership, should not be neutral in its economic consequences.
Because betrayal has a cost.
And when the law ignores it, that cost is not erased—it is simply transferred.
Often to the one who kept the promise.
This is not about shame.
It is about justice.
And perhaps the time has come to stop treating adultery as a private mistake—and start seeing it as what it often becomes: a breach of trust with real-world, measurable harm.
Only then can we begin to write laws that don’t just end marriages fairly,
but respect the value of the commitments that once began them.