Why can a marriage be annulled because one spouse lacked the legal capacity to marry?

In family law, an annulment is a legal decree that declares a marriage invalid, effectively treating it as though it never existed from its inception.1

A marriage may be annulled due to a lack of legal capacity because the marriage contract is considered fundamentally defective. For a marriage to be valid, both parties must be capable of providing meaningful consent. Legal capacity is often challenged on the following grounds:12

• Age: Parties must meet a minimum legal age to ensure they possess the maturity to consent. Marriages involving individuals below these thresholds may be subject to annulment.21
• Mental Capacity: Individuals may be legally disqualified from marrying if they lack the mental ability to understand or provide valid consent to the marriage contract.21
• Prior Obligations: A person lacks the capacity to enter a new marriage if they are already legally bound by a pre-existing marriage.1

Because annulment seeks to restore parties to their status before the marriage, courts generally require clear proof of the defect and may apply the "clean hands" doctrine, which can prevent a party from seeking an annulment if they knowingly entered the marriage despite the lack of capacity.1