Contra bonos mores is a Latin phrase meaning “against good morals.” Courts use it as a ground to refuse enforcement of a contract, or to bar a legal claim, when the agreement or the conduct behind it offends moral standards the legal system treats as fundamental. In the United States and other common law countries, the same idea usually travels under the label “public policy,” but the effect is identical: the contract is void, and the courthouse door closes.
The doctrine reaches into contract law first, and from there into tort claims, family law, and immigration proceedings. Civil law countries such as Germany and South Africa still apply it by name. American courts rarely use the Latin, but the principle is alive in every jurisdiction.
What Makes a Contract Against Good Morals
The conflict with good morals can come from any of three places: the subject matter of the contract, the performance one side has to render, or the purpose the parties had in mind. Often it’s a combination of what the contract says and the circumstances surrounding it that pushes the deal across the line.
The classic illustration is Pearce v. Brooks, an 1866 English case. A carriage maker sold a decorative horse-drawn carriage to a woman he knew was a prostitute, understanding she would use it to attract clients. When she didn’t pay, the court refused to let him sue. The carriage itself was a legal product. No statute banned the sale. But the seller knowingly supplied something for an immoral purpose, and the law would not help him collect.
In the United States, the same reasoning shows up as a public policy analysis. The Supreme Court set out the rule in Armstrong v. Toler (1826): “Where a contract grows immediately out of and is connected with an illegal or immoral act, a court of justice will not lend its aid to enforce it.”1Justia. Armstrong v. Toler, 24 U.S. 258 (1826) That principle still governs.
In transnational commercial law, the same idea limits freedom of contract to protect values the international community treats as non-negotiable: prohibitions on bribery, money laundering, drug trafficking, and contracts made in violation of United Nations embargoes.
Illegal Contracts Versus Immoral Contracts
The two categories overlap but are not the same. An illegal contract directly violates a statute. An agreement to sell controlled substances is illegal on its face. An immoral contract does not break any specific law but offends societal standards deeply enough that courts refuse to enforce it.
The carriage in Pearce v. Brooks was legal. What made the sale unenforceable was the seller’s knowledge of what it would be used for. That gap between “legal” and “enforceable” is where contra bonos mores does its work. A judge has to decide what the community considers fundamentally unacceptable without a statute to point to, which is why outcomes are harder to predict here than in most contract disputes.
What Happens When a Court Voids the Contract
If a contract violates good morals, it is void. Not voidable at one side’s option. Void, meaning it produces no enforceable obligations at all. The judge has no discretion to salvage it, and it doesn’t matter whether the parties knew about or intended the moral violation.
The harsher consequence is what happens to money or property already exchanged. A related doctrine, in pari delicto (“in equal fault”), applies. When both parties knowingly took part in the immoral arrangement, courts will not step in to sort out who owes what back to whom. Someone who paid under a contract later voided as contra bonos mores can lose that money entirely, with no legal mechanism to recover it. The doctrine of “unclean hands” reinforces the same result: courts are deliberately reluctant to grant relief to a party whose own conduct is part of the problem.
The practical consequence is that entering a deal that sits near the moral boundary carries a risk larger than losing the deal. You can lose what you already put in.
Contra Bonos Mores in Family Law
Family courts apply the principle mainly through the enforceability of marital agreements. Prenuptial and postnuptial contracts can be struck down when specific provisions violate public policy. Courts have consistently held that provisions encouraging divorce or infidelity are unenforceable. A clause awarding a financial bonus to a spouse who files for divorce is the kind of term a court will refuse to honor, because it creates an incentive that undermines the marriage itself.
Child custody and support face an even stricter rule. Parents cannot bargain these away in advance. A prenuptial clause that tries to predetermine custody or waive child support will be struck regardless of what both parties agreed to, because the child’s welfare is a societal interest that outweighs private agreement.
A parent’s moral conduct can factor into custody decisions, but courts today frame this through the “best interests of the child” standard rather than invoking contra bonos mores by name. Behavior matters only insofar as it affects the child, not as a freestanding moral judgment.
Cohabitation agreements between unmarried partners sit in a delicate spot. Courts have generally held them enforceable when the consideration is independent of the sexual relationship. An agreement based on companionship, housekeeping, or shared finances can survive scrutiny. One that is fundamentally an exchange of financial support for sexual services will not.
The Tort Law Cousin: Ex Turpi Causa
The same moral principle appears in tort claims through ex turpi causa non oritur actio, “from a dishonorable cause, no action arises.” This common law defense prevents a claimant from recovering damages when their own illegal or seriously immoral conduct is connected to the injury. Someone hurt while taking part in a criminal enterprise may find a court unwilling to award compensation.
Severity matters. Serious criminal conduct such as violence or drug trafficking will almost certainly trigger the defense. Minor regulatory violations typically will not. Conduct that is immoral but not criminal gets closer scrutiny, with courts weighing how directly the wrongdoing connects to the harm.
Moral Turpitude in Immigration and Licensing
Moral turpitude is a close cousin of contra bonos mores, and its consequences reach well beyond any criminal sentence. A crime involving moral turpitude generally involves intent to commit fraud, intent to steal with permanent deprivation, or intent to inflict serious bodily harm. Some offenses involving reckless or malicious conduct also qualify.
For noncitizens, the stakes are severe. Under the Immigration and Nationality Act, a conviction for a crime involving moral turpitude can make someone inadmissible to the United States or subject to deportation. Federal regulations tie the determination to “the moral standards generally prevailing in the United States,” which builds a community-based definition into the rule itself.2eCFR. 22 CFR 40.21 – Crimes Involving Moral Turpitude and Controlled Substances Limited exceptions exist for offenses committed before age fifteen and for certain juvenile adjudications, but a person convicted of multiple offenses involving moral turpitude is inadmissible regardless of age at the time of the crime.
Professional licensing is the other area where these determinations bite. Boards regulating attorneys, teachers, physicians, and public notaries have historically treated moral turpitude convictions as grounds to deny or revoke a license. Several states have moved away from that standard, enacting laws that prohibit licensing boards from relying on moral turpitude and requiring instead a direct connection between the specific criminal conduct and the duties of the licensed profession. The change reflects a view that the vagueness of the concept gives licensing boards too much discretion.
The Standard Shifts Over Time
What counts as “against good morals” is not fixed, and that’s the doctrine’s biggest source of unpredictability. Courts apply moral standards as they exist at the time of the decision, not as they existed when the contract was signed or the conduct occurred. Agreements struck down a century ago as immoral may be perfectly enforceable now, and some conduct once treated as ordinary may cross the line today.
The adaptability lets the doctrine keep pace with changing values. It also means that two judges looking at the same facts can reach opposite conclusions about whether a deal is merely aggressive or genuinely repugnant. When financial stakes are meaningful, and especially when in pari delicto could bar any recovery of what was already exchanged, that unpredictability is itself part of the risk.