CONSENT. - In its broadest meaning it is the adherence of the will to the idea presented by the intellect: it is a necessary element for the human act to be called free and voluntary and thus able to enter the ethical order (v. ATTO UMANO). Human action is voluntary insofar as it proceeds from the deliberating will, that is, illuminated by the intellect which perceives the relation of the act to its end: all actions performed without deliberation and the consent of the will (in drunkenness, in grave fear that disturbs reason, in violence that constrains a reluctant will, in first movements, in sleep, etc.) are neither voluntary nor free and are therefore not susceptible of moral evaluation. Even actions in which deliberation and consent are not full and perfect are not perfectly free and voluntary and are less responsible (v. PECCATO, mortal and venial).
In law one speaks of consent in two different meanings: in the sense of the meeting of two wills that agree in regulating one or more juridical relationships, and in the sense of the approval, by a person having authority (public or private), of a decision and an act of another.
In the first meaning the notion of consent is relevant in the matter of contracts (v. CONTRATTO). Indeed, in contrast to the Roman principle by which the principal mode of transfer of ownership was the traditio rei, the delivery of the thing, the radical and great innovation of the modern codes, which derive from the Napoleonic one (Albertine, Italian), consists in having fixed the moment and the effect of the transfer of a property or a right in the legitimate manifestation of consent. The innovation is a conquest on the logical line and on the juridical line: indeed the contract is an essentially and juridically bilateral transaction and already exists in the meeting of two wills which, being internal spiritual faculties, cannot be seen, evaluated and have social repercussions except insofar as they are manifested: in manifested consent. One now understands the classic Roman definition of contract: Duorum vel plurium in idem placitum consensu.
The external manifestation of the will or internal consent can occur in different ways and by different means: expressly or tacitly (even silence can manifest a will, when there are such circumstances that to be silent is equivalent to an explicit answer: such equivalence exists, however, only when the one who is silent would in any case have had expressly to consent or dissent).
It may happen that a will different from that actually existing in the subject's consciousness is manifested: this occurs either through mental reservation (v.) or through error (v.), or through simulation (v.).
It has been said that in modern law consent is of itself transferative of rights; but if the contract is made between absent parties, when is consent held to be perfected? The principles of the Italian Civil Code can be summarized thus: the agreement is considered reached and therefore the contract concluded at the moment in which the one who made the proposal has knowledge of the acceptance of the other party (art. 1326). Such knowledge is presumed at the moment in which the acceptance reaches the address of the proposer, unless the latter proves that he was, without fault of his own, unable to have notice of what had reached him (art. 1335). Until the contract is concluded, the proposal and the acceptance may as a rule be revoked, subject to compensation of whoever in good faith has begun performance (art. 1328); when, however, it is a question of contracts with unilateral obligations of the proposer (suretyship, offer of the surety), the proposal is irrevocable when it comes to the knowledge of the recipient (art. 1333).
The defects of consent, listed by jurisprudence, are causes that influence the formation of the act of will so that without them the consent would not have existed or would have been different. In this case there is therefore a will actually formed and manifested, and another neither formed nor manifested, but which would have been formed and manifested if the cause had not influenced it. Such causes are: error, fraud (v.), violence (v.).
As regards particularly consent in custom and in marriage, v. the respective entries.