15. Mental Illness Or Defect


(1) A person incurs only voidable contractual duties by entering into a transaction if by reason of mental illness or defect

(a) he is unable to understand in a reasonable manner the nature and consequences of the transaction, or

(b) he is unable to act in a reasonable manner in relation to the transaction and the other party has reason to know of his condition.

(2) Where the contract is made on fair terms and the other party is without knowledge of the mental illness or defect, the power of avoidance under Subsection (1) terminates to the extent that the contract has been so performed in whole or in part or the circumstances have so changed that avoidance would be unjust. In such a case a court may grant relief as justice requires.


a. Rationale. A contract made by a person who is mentally incompetent requires the reconciliation of two conflicting policies: the protection of justifiable expectations and of the security of transactions, and the protection of persons unable to protect themselves against imposition. Each policy has sometimes prevailed to a greater extent than is stated in this Section. At one extreme, it has been said that a lunatic has no capacity to contract because he has no mind; this view has given way to a better understanding of mental phenomena and to the doctrine that contractual obligation depends on manifestation of assent rather than on mental assent. See 2, 19. At the other extreme, it has been asserted that mental incompetency has no effect on a contract unless other grounds of avoidance are present, such as fraud, undue influence, or gross inadequacy of consideration; it is now widely believed that such a rule gives inadequate protection to the incompetent and his family, particularly where the contract is entirely executory.

b. The standard of competency. It is now recognized that there is a wide variety of types and degrees of mental incompetency. Among them are congenital deficiencies in intelligence, the mental deterioration of old age, the effects of brain damage caused by accident or organic disease, and mental illnesses evidenced by such symptoms as delusions, hallucinations, delirium, confusion and depression. Where no guardian has been appointed, there is full contractual capacity in any case unless the mental illness or defect has affected the particular transaction: a person may be able to understand almost nothing, or only simple or routine transactions, or he may be incompetent only with respect to a particular type of transaction. Even though understanding is complete, he may lack the ability to control his acts in the way that the normal individual can and does control them; in such cases the inability makes the contract voidable only if the other party has reason to know of his condition. Where a person has some understanding of a particular transaction which is affected by mental illness or defect, the controlling consideration is whether the transaction in its result is one which a reasonably competent person might have made.