INCAPACITY. - In moral theology and in law it is the lack of certain conditions necessary for acting, such that a subject finds himself in the impossibility of performing a determinate act. Since the necessity of determinate conditions has its origin in different sources, a distinction is drawn between natural incapacity and positive incapacity. Thus, for example, the incapacity to succeed of one not yet conceived is called natural, as is the incapacity to contract Marriage of one already bound by the bond of a previous Marriage, etc.; on the other hand, the incapacity to succeed of the unworthy is called positive, as is the incapacity to contract Marriage of one who is bound to the other party by a bond of consanguinity in the 2nd or 3rd degree of the collateral line, etc. Natural incapacities must be established with certainty from the natural law; divino-positive incapacities must likewise result with certainty from Revelation through the teaching of the Church; positive human incapacities must result from an unequivocal provision of human law, whether ecclesiastical or civil.
General capacity with regard to rights and obligations is a necessary consequence of being a person (v. CAPACITÀ); by contrast, specific capacity with respect to the rights and obligations deriving from or guaranteed by a determinate juridical order derives normally from the status of citizen. The general causes that serve to modify a person's capacity by creating incapacities are: age, sex, origin, domicile, family relationships, rite, physical health, a penal conviction. Besides these general causes, individual juridical orders consider others of their own. In any case, since incapacity for a determinate action represents a diminution of personality, it must not be presumed, but must be unequivocally established.
As for the consequences of actions performed by an incapable person, it must be seen whether they present themselves as a true inability or only as a prohibition. For example, the impediments to Marriage in canon law are incapacities that present themselves as inability, and consequently the Marriage thus contracted is invalid. On the contrary, prohibitive impediments present themselves only as prohibitions, and consequently the Marriage eventually contracted proves valid. If the incapacity presents itself as a true inability, the act performed does not exist and can have no consequence; otherwise the act exists in a condition of irregularity that can entail various consequences, among them annulment and rescission. Owing to the practical requirements of a system, it may happen that an act which by nature is non-existent (for example, a contract stipulated by a person incapable of understanding and willing: Italian Civil Code, art. 1425) must be held to exist and to be operative at least until it is annulled, which gives rise to a true conflict between the internal forum and the external forum.