Contractual incapacity
Contract Law

The incapacity of one or more of the contracting parties may defeat an otherwise valid contract. Prima facie however, the law presumes that everyone has a capacity to contract; so that, where exemption from liability to fulfil an obligation is claimed by reason of want of capacity, this fact must be strictly established on the part of the person who claims the exemption.

In English law, four classes of individuals are subject to some degree of personal contractual incapacity. These are minors, married women (although little or no vestige of their contractual incapacity remains), mentally disordered persons, and drunk persons. Abnormal weakness of mind short of such mental disorder as prevents a person understanding the nature of the transaction, or immaturity of reason in one who has attained full age, or the mere absence of skill upon the subject of the particular contract, affords per se no ground for relief at law or in equity, although certain cases, undue influence or unconscionable dealing by the other party or inequality of bargaining power may permit the transaction to be set aside as inequitable - that is to say that the contract is deemed never to have been formed.