1881. Qualities Necessary in the Parties Contractant.—The parties contractant must have the following qualities:
(a) from natural law it is necessary that they have the use of reason sufficient to understand what they are doing. Incompetent are babies and the insane, and also those who are totally drunk or otherwise temporarily deranged. Less competent are the half-witted and those who need a guardian in important matters;
(b) from positive law it is necessary that they be not legally excluded. In Canon Law administrators of church property and solemnly professed religious are unable to make certain contracts (Canons 1527, 536). In civil law there are restrictions on the contractual powers of minors, wives, aliens, guardians and corporations. Persons not yet conceived are not capable in civil law of receiving a donation, and there are many prohibitions against the tender or acceptance of gifts by those who can reasonably be suspected of exercising undue influence or of being subject to undue influence.
1882. Legal Privileges of Minors.—The law grants certain benefits to minors and the like; for example, in some cases they are not bound by a non-executed agreement, while the other party is bound, or in an executed contract they may recover property without restoring or offering to restore the consideration, if they have nothing with which to replace it.
(a) Minors and other persons who are legally incompetent to contract, may avail themselves of the benefits of the law with a good conscience, if they are in good faith; for it is just that the law should protect those who are unable to protect themselves, and those who make contracts with such persons should know that they (the competent parties) act at their own risk.
(b) Minors and other persons legally incompetent may not avail themselves of the benefit of the law if they have acted in bad faith (e.g., if a minor by deceit induced the other party to sell to him).
1883. Qualities Necessary for Valid Consent.—The agreement or consent of the contracting parties must have the following qualities:
(a) it must be internal, that is, one must accept in will and not merely in words the proposal or consideration offered by the other party. If one consents only to the form of the contract, the contract is null, and the same is probably true if one does not accept internally the obligations of the contract; if one consents to the obligations, but does not intend to fulfill them, the contract is valid, but unlawful. One who contracts invalidly sins, and is bound in the external forum to keep the contract seriously made, and in the internal forum to repair the damage to the other party by giving true consent or making restitution. One who contracts unlawfully also sins, and is bound to the engagement;
(b) it must be external, that is, one must manifest in some sensible way one’s agreement to the proposition contained in an offered contract. Silence gives consent only when the contract is favorable to the party who is silent, or when that party should and easily could manifest his lack of consent, if the proposal did not please him. In the case of contracts between parties who are not in each other’s presence, the intimation to the offerer of the offeree’s acceptance is not necessary for validity, if the contract is gratuitous; but the contrary seems to be true, at least _per se_, if the contract is onerous. We shall speak later (1885) on the legal formalities required in contracts;
(c) it must be mutual, that is, there must be a meeting of minds in the same sense, or agreement of both parties to the same thing. Mutuality requires that consent be contemporaneous, that is, that the acceptance of one be given while the offer of the other still holds good. But it does not require that the parties be in each other’s presence, or that they contract through direct personal communication, or (at least according to natural law) that the knowledge of the accomplishment of mutual agreement be known to the offerer. The law in the United States generally is that an offer may be withdrawn immediately or after a reasonable time, unless it was made on time for a consideration; and that a contract between the absent begins only on receipt by the offerer of the acceptance of the offeree, if the former stipulated for this, or if the offerer uses one means of communication as his agency and the offeree another. In other cases it begins the moment that acceptance is entrusted to the agent of the offerer;