In general, all persons may enter into contracts; and when a contract is made, the law presumes the competency of the parties. If, therefore, a party rests his action or his defence upon the incompetency or incapacity of himself or of the other party, this must be proved. (a) This incompetency may he absolute and entire, or limited and partial; in some cases a contract is void as to both parties, and in others only as to one; in some cases void, and in others voidable. We shall consider these questions as we proceed.

As the essence of a contract is an assent or agreement of the minds of both parties, where such assent is impossible, from the want, immaturity, or incapacity, of mind, there can be no perfect contract. On this ground rests, originally, the disability of infants. We will first consider this class of disabled persons.