Catechism of the Catholic Church

2366 Fecundity is a gift, an end of marriage, for conjugal love naturally tends to be fruitful. A child does not come from outside as something added on to the mutual love of the spouses, but springs from the very heart of that mutual giving, as its fruit and fulfillment. So the Church, which "is on the side of life" ¹⁵¹ teaches that "it is necessary that each and every marriage act must remain ordered per se to the procreation of human life." ¹⁵² "This particular doctrine, expounded on numerous occasions by the Magisterium, is based on the inseparable connection, established by God, which man on his own initiative may not break, between the unitive significance and the procreative significance which are both inherent to the marriage act." ¹⁵³

2367 Called to give life, spouses share in the creative power and fatherhood of God. ¹⁵⁴ "Married couples should regard it as their proper mission to transmit human life and to educate their children; they should realize that they are thereby cooperating with the love of God the Creator and are, in a certain sense, its interpreters. They will fulfill this duty with a sense of human and Christian responsibility." ¹⁵⁵

2368 A particular aspect of this responsibility concerns the regulation of procreation. For just reasons, spouses may wish to space the births of their children. It is their duty to make certain that their desire is not motivated by selfishness but is in conformity with the generosity appropriate to responsible parenthood. Moreover, they should conform their behavior to the objective criteria of morality:

When it is a question of harmonizing married love with the responsible transmission of life, the morality of the behavior does not depend on sincere intention and evaluation of motives alone; but it must be determined by objective criteria, criteria drawn from the nature of the person and his acts, criteria that respect the total meaning of mutual self-giving and human procreation in the context of true love; this is possible only if the virtue of married chastity is practiced with sincerity of heart. ¹⁵⁶

2369 "By safeguarding both these essential aspects, the unitive and the procreative, the conjugal act preserves in its fullness the sense of true mutual love and its orientation toward man's exalted vocation to parenthood." ¹⁵⁷

2370 Periodic continence, that is, the methods of birth regulation based on self- observation and the use of infertile periods, is in conformity with the objective criteria of morality. ¹⁵⁸ These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom. In contrast, "every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" is intrinsically evil: ¹⁵⁹

Thus the innate language that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory language, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality.... The difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle . . . involves in the final analysis two irreconcilable concepts of the human person and of human sexuality. ¹⁶⁰

2371 "Let all be convinced that human life and the duty of transmitting it are not limited by the horizons of this life only: their true evaluation and full significance can be understood only in reference to man's eternal destiny." ¹⁶¹

2372 The state has a responsibility for its citizens' well-being. In this capacity it is legitimate for it to intervene to orient the demography of the population. This can be done by means of objective and respectful information, but certainly not by authoritarian, coercive measures. The state may not legitimately usurp the initiative of spouses, who have the primary responsibility for the procreation and education of their children. ¹⁶² In this area, it is not authorized to employ means contrary to the moral law.