2618. The Morality of Venereal Acts of Marriage.—(a) Non-consummated Acts.—These acts, whether internal or external, are lawful _per se_ when they are used only as accessories to the act of marriage or as means to foster or preserve conjugal love, for the acts are meant by God to serve the purposes mentioned (2510). But _per accidens_ there may be venial sin, on account of inordinateness in the motive (i.e., when only pleasure is intended), or in the manner (i.e., when due decency is not observed). There is mortal sin when these acts are not referred to the lawful conjugal act, but either directly or indirectly to pollution, namely, when there is foreseen proximate danger of pollution and the acts are either solitary or cooperative but performed without sufficient reason (such as expressions of special affection), for pollution is gravely sinful in the married, as well as in the single state (see 2539 sqq.).
(b) Natural Consummated Act.—This act in itself is not only lawful, but meritorious, because it exercises such virtues as obedience (Gen., i. 28), justice (I Cor., vii. 3 sqq.), and love of the common good and religion (Tob., viii. 9). Since marriage intercourse has for its ends not only reproduction, but also the expression of mutual love and the allaying of concupiscence, it is lawful even when conception is impossible or less probable, as when the parties are sterile, or the woman is pregnant, or during the so-called agenesic period, or at the time of lactation. It is a venial sin to exercise the conjugal act when one excludes every motive except that of pleasure (Denziger, n. 1159); and there may be even mortal sin on account of circumstances, such as place (e.g., scandal to others present), manner (e.g., external immoderation, internal desire of another person), evil consequences (e.g., when one of the parties has a contagious or veneral disease, when abortion will likely result, etc.).
(c) Unnatural Consummated Acts.—Pollution is mortally sinful (2535 sqq.), and is worse in married than in single persons, as being an injury to the faith pledged in marriage; and hence it is not lawful to practise it even for the purpose of artificial fecundation. Rectal copulation is also gravely sinful, being unnatural lust (see 2534) and a violation of conjugal faith. The usual forms of unnatural vaginal coition, which are very much practised today, are contraceptive in purpose, and are of two general kinds in the procedure—the physiological or preventive, which uses instruments to keep the semen from the uterus (such as sponges or pessaries for the female, condoms or protectors for the male), or which employs douches or syringes to remove semen from the vagina, or uses chemicals to devitalize it.
2619. Nota.—(a) Non habetur onanismus, nec peccatum, si copula abrumpitur, ex necessitate (v.g., ad vitandum scandalum persona inopinate supervenientis), vel ex utilitate, mutuo dato consensu et periculo pollutionis excluso; nam seminatio extra vas, aut involuntaria est, aut nulla.
(b) Non habetur contraceptio nec peccatum, sed potius actus honestus, si, ob defectum physicum viri vel mulieris, naturae adjuvetur mediis artificialibus ut copula fiat, vel ut semen introducatur in uterum; nam fini matrimonii non obstat, sed obsecundat iste modus agendi.
(c) Artificial Insemination. The subject-matter of the latter part of the preceding paragraph is distinguished from several unlawful practices considered by moralists under the heading of artificial insemination. Pope Pius XII on several occasions has given a clear, accurate and complete statement of Catholic teaching on the subject. We append here his texts:
1) The practice of artificial insemination, when it refers to man, cannot be considered, either exclusively or principally, from the biological and medical point of view, ignoring the moral and legal one.
Artificial insemination, outside of marriage, must be condemned as essentially and strictly immoral.
Natural law and divine positive law establish, in fact, that the procreation of a new life cannot but be the fruit of marriage. Only marriage safeguards the dignity of the spouses (principally of the wife in the present case) and their personal good. It alone provides for the well-being and education of the child.
It follows that no divergence of opinion among Catholics is admitted on the condemnation of artificial insemination outside of marriage. The child conceived in those conditions would be, by that very fact, illegitimate.