Capacity and consent to marry are the two things every state requires from each person before a marriage is legally valid. Capacity means you meet the baseline qualifications: sufficient age, mental competence, and no disqualifying relationship like an existing spouse or a close blood tie. Consent means your agreement is voluntary and based on honest information. When either is missing, the marriage can be challenged or treated as if it never existed.
Legal Age
Eighteen is the age of majority for marriage in every state. Once you reach it, you can marry without anyone else’s permission.
Below eighteen, the rules vary and have been tightening quickly. As of 2025, roughly nineteen U.S. jurisdictions have banned marriage under eighteen entirely, with no exceptions. The remaining states still allow minors to marry under certain conditions. Some require parental consent for sixteen- and seventeen-year-olds. Others require a judge to review the petition and decide whether the marriage serves the minor’s best interest. A handful of states still have no statutory minimum age at all, meaning a court could theoretically approve a very young marriage if parental consent and judicial approval both exist.
Where states still permit minor marriages, the trend is toward requiring judicial involvement rather than parental consent alone. A judge typically weighs the minor’s maturity, whether the decision is voluntary, and whether the marriage serves the minor’s welfare rather than someone else’s interests.
A marriage performed without the required age-based authorization is usually voidable, meaning it remains legally effective until someone challenges it. If the underage spouse continues in the marriage after turning eighteen without seeking an annulment, most states treat the original defect as cured.
Mental Competence
Both parties must have the mental ability to understand what marriage means at the moment they exchange vows. Courts don’t demand a sophisticated grasp of family law. The standard is whether a person can comprehend the basic nature of the commitment, the responsibilities it creates, and the consequences of entering it.
Temporary impairment is the scenario people picture first: the Las Vegas wedding after too many drinks. If someone is so intoxicated, whether from alcohol, prescription medication, or other substances, that they genuinely cannot understand they are getting married, the ceremony doesn’t produce valid consent. Proving this later is the hard part. A court wants evidence of how impaired the person was during the actual ceremony, not the night in general. A couple of drinks at dinner won’t cut it; the impairment has to be severe enough that the person couldn’t grasp what was happening.
Long-term conditions can also prevent someone from having capacity: serious mental illness, advanced dementia, severe intellectual disabilities. Courts focus on the person’s state of mind at the time of the ceremony, not their general diagnosis. Someone with a mental health condition who experiences lucid periods may have full capacity during one of them, even if they lack it at other times. Medical evaluations and testimony from people present at the ceremony carry significant weight.
Guardianship Doesn’t Automatically Block Marriage
A common misconception is that being under a court-ordered guardianship means a person cannot marry. It doesn’t. Courts have consistently distinguished the standard for needing a guardian from the standard for capacity to marry. Someone might need help managing finances or daily decisions and still understand what marriage is and choose it freely.
Many states require the guardian’s consent before a ward can marry. But even when that consent is withheld, a marriage performed without it is often presumed valid unless someone can prove the ward lacked the mental capacity to understand the marriage. The test remains the same: could the person grasp the nature, effect, and consequences of the commitment? Because the right to marry is constitutionally protected,1Justia Law. Loving v. Virginia, 388 U.S. 1 (1967) any restriction a guardian imposes on it has to be narrowly justified. In some states, a person who wants to marry someone under guardianship can petition the court to modify the guardianship order to allow the marriage.
Voluntary Consent
Even if both parties have full legal capacity, the marriage still requires genuine consent, meaning a real agreement between two people who actually want to be married. Consent that is coerced or tricked out of someone doesn’t count.
Duress and Coercion
Duress means one party was pressured into the marriage by threats or force severe enough to override their free will. It can include physical violence, threats of harm to the person or their family, or threats of criminal prosecution. The pressure has to be real and present at the time of the marriage, not a vague feeling of family expectation. A parent expressing strong disappointment is not duress. A parent threatening to disown a child and leave them homeless may be, depending on the circumstances.
When duress is proven, the marriage is voidable. The coerced spouse can file for an annulment, and if the court agrees, the marriage is treated as though it never happened. The challenge is almost always evidence: proving what threats were made privately, often months or years before anyone takes legal action.
Fraud Going to the Essentials
Not every lie told before a wedding justifies an annulment. Courts traditionally apply what’s called the “essentials of the marriage” test: the fraud has to involve something fundamental to the marriage itself. Misrepresentations about the ability to have children, willingness to consummate the marriage, or intent to actually live together as spouses have historically been the strongest grounds. Lies about wealth, personal history, or character, however outrageous, have traditionally been harder to use as a basis for annulment, because courts didn’t consider them central to the marriage contract itself.
The modern trend in many courts is toward a broader view. Judges increasingly consider whether the deception was so serious that the other spouse would never have agreed to the marriage if they had known the truth. Hiding an active violent criminal history or a serious communicable disease, for example, might support an annulment even though those facts don’t fit neatly into the traditional categories. The law here is genuinely unsettled and varies significantly by state.
Disqualifying Relationships
Some legal barriers operate as absolute disqualifiers. No amount of consent or capacity can overcome them, and a marriage performed in violation of these rules is typically void from the start.
Close Blood Relatives
Every state prohibits marriage between close blood relatives. Direct ancestors and descendants (parent-child, grandparent-grandchild) and siblings cannot marry under any circumstances. These prohibitions are universal and carry no exceptions.
First cousins are a different story. Roughly nineteen states place no restriction on first cousins marrying. About thirty states ban or limit the practice, with some providing narrow exceptions. Several allow first cousins to marry only if both are over a certain age (typically fifty or older) or can demonstrate they cannot have children. A small number of states criminalize sexual relationships between first cousins under their incest statutes.
Bigamy
You cannot marry someone new while still legally married to someone else. Every state criminalizes bigamy, and any marriage entered while a prior marriage remains undissolved is void. Unlike a voidable marriage, a bigamous union cannot be fixed by the parties’ continued cohabitation or by any other action short of dissolving the first marriage and starting over.
Bigamy is typically treated as a felony, though the severity varies widely. Penalties can range from less than a year in jail in some states to ten years in prison in others, often with substantial fines. People sometimes commit bigamy without realizing it, believing a prior divorce was finalized when it wasn’t, or assuming a long separation is equivalent to a legal divorce. Neither belief provides a defense in most states. If you have any doubt about whether a prior marriage was properly dissolved, confirming it through court records before remarrying is the only safe approach.
Void Versus Voidable Marriages
This distinction matters more than most people realize.
A void marriage has no legal effect from the moment it is performed. It is as though the ceremony never happened. Marriages between close blood relatives, bigamous marriages, and in some states marriages involving minors below a certain age fall into this category. Technically, a void marriage doesn’t even require a court order to be treated as invalid. As a practical matter, getting a court declaration of nullity is almost always necessary to clear up legal records and protect both parties’ rights.
A voidable marriage is legally valid unless and until someone successfully challenges it. Marriages entered under duress, through fraud, or while one party lacked mental capacity are typically voidable. The crucial difference: if no one ever files for an annulment, a voidable marriage remains a real, enforceable marriage with all the usual legal consequences. And if the grounds for challenging it are cured (the underage spouse turns eighteen, the intoxicated spouse sobers up and continues in the marriage, the coerced spouse stays voluntarily after the threat is removed), the right to annul may be lost entirely.
What Happens to Property and Support If a Marriage Is Annulled
When a marriage is annulled, the legal fiction is that it never existed. That creates a real problem for property, debts, and support obligations accumulated during what both parties believed was a valid marriage. In a divorce, courts divide marital property and may award spousal support. In an annulment, there is technically no “marital” property to divide because there was technically no marriage.
The harsh consequences of this rule led to the development of the putative spouse doctrine, which a number of states have adopted. Under this doctrine, a person who entered a marriage in genuine good faith, truly believing it was legally valid, can still receive many of the financial protections a legal spouse would get. That can include rights to property division, wrongful death claims, workers’ compensation benefits, and a share of the other party’s estate. The doctrine exists to prevent the injustice of stripping all marital rights from someone who did nothing wrong and had no reason to know the marriage was defective.
Not every state recognizes the putative spouse doctrine, and the details vary among those that do. If you are facing a potential annulment and acquired significant property or debts during the relationship, your state’s approach could have substantial financial consequences.
Immigration Marriage Fraud Is a Separate Problem
Capacity and consent govern whether a marriage is valid under state law. Immigration law adds a separate layer: a marriage can be technically valid and still produce federal criminal exposure if it was entered to evade immigration law rather than to build a genuine life together. Anyone who knowingly enters a marriage for that purpose faces up to five years in federal prison, a fine of up to $250,000, or both.2Office of the Law Revision Counsel. 8 USC 1325 – Improper Entry by Alien Both the sponsoring citizen and the immigrant spouse can face prosecution.
USCIS evaluates whether a marriage is genuine by looking for concrete evidence that the couple intended to build a life together at the time they married. A valid marriage certificate alone is not enough. The agency looks for documentation like joint property ownership, a shared lease, commingled bank accounts, birth certificates of children born to the couple, and sworn statements from people with personal knowledge of the relationship.3U.S. Citizenship and Immigration Services. Volume 6, Part B, Chapter 6 – Spouses A finding of marriage fraud results in denial of immigration benefits along with potential criminal referral.