mental infirmity

if a person is under guardianship (under the care of someone), that individual does not have the capacity to incur contractual duties. More generally, for mental illness or defect, a voidable contract is created. However, an extreme level of incompetence is required. But where the contract was made on fair terms and with the other party without the knowledge of mental illness or defect, a court may grant relief on equitable terms as justice requires.