INCAPACITY. - In moral theology and in law, it is the lack of certain conditions necessary for acting, so that a subject finds themselves in the impossibility of performing a specific act. Since the necessity of certain conditions arises from different sources, a distinction is made between: 1. natural and 2. positive incapacity. Thus, for example, it is said: natural incapacity to succeed is that of the unborn, to contract marriage that of one already bound by a previous marital bond, etc.; whereas positive incapacity to succeed is that of the unworthy, to contract marriage that of one bound to the other party by a bond of consanguinity in the second or third degree of the collateral line, etc. Natural incapacities must be consistent with the certainty of natural law; divinely-positive incapacities must likewise result with certainty from Revelation through the teaching of the Church; human-positive incapacities must result from an unequivocal provision of human law, whether ecclesiastical or civil.
General capacity in relation to rights and obligations is a necessary consequence of being a person (v. CAPACITY); instead, specific capacity with regard to rights and obligations arising or guaranteed by a particular legal system normally derives from the state of citizenship. The general causes that influence the modification of a person’s capacity, creating incapacities, are: age, sex, origin, domicile, family relationships, rite, physical health, and a criminal conviction. In addition to these general causes, individual legal systems consider other particular ones. In any case, since incapacity for a specific 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 incapacitated person, it is necessary to determine whether they appear as true inability or merely as prohibition. For example, diriment impediments to marriage in canon law are incapacities that appear as inability, and consequently the marriage thus contracted is invalid. On the contrary, prohibitive impediments appear only as prohibitions, and consequently any marriage contracted remains valid. If incapacities appear as true inability, the act performed does not exist and can have no consequences; otherwise, the act exists in a condition of irregularity that may entail various consequences, including annulment and rescission. For the practical exigencies of a system, it may happen that an act which by nature is non-existent (e.g., a contract entered into by a person not of sound mind and will: Cod. civ. it., art. 1425) must be considered as existing and operative until at least it is annulled, which gives rise to a real conflict between the internal forum and the external forum.