§ III. On incest

495. Definition. - Incest is concubitus with a person joined by kinship or affinity within the degrees in which it is not licit to enter Matrimony. But kinship is threefold: natural, namely among blood-relations up to the fourth degree inclusive (the same is valid concerning affines); spiritual, arisen from Baptism or Confirmation; and legal, proceeding from adoption.

Principles. - I. Incest is a special and most grave sin. For it is opposed both to chastity, and to the piety and reverence owed to kin and affines. Hence in Leviticus⁴ it is punished by the penalty of death; and Blessed Paul¹ gravely rebukes the incestuous man, handing him over to Satan that he may be corrected.

II. It is certain that at least four species of incest are given which must be explained in Confession. - For they commonly teach: Incest among blood-relations or affines differs in species, both 1° from incest among spiritual relatives, and 2° from incest among legal relatives, because they arise from a formally diverse root: indeed, according to St. Thomas,² by copula among spiritual relatives, sacrilege is committed in the manner of incest. 3° Likewise incest among blood-relations or affines in the first degree of the direct line differs in species from every incest of an inferior degree; because conjunction between parents and children, and especially between mother and son, is altogether prohibited by the right of nature on account of the reverence owed to parents; likewise from the same motive, says St. Alphonsus, conjunction between father-in-law and daughter-in-law, between stepmother and stepson, is prohibited.³ See the rest in n. 1365. q. 2°.

Note. - A confessor more probably does not commit incest in having intercourse with a penitent; for there is no spiritual kinship between them, since this arises only from Baptism and Confirmation. But a pastor sinning with his parishioner offends against justice, from which he is bound to feed his sheep not only by word, but also by example.⁴ Several say the same of a guardian toward a ward, and of all to whom the care of minors has been committed.⁵