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 fulfilment. So the Church, which is on the side of life teaches that it is necessary that each and every marriage act remain ordered per se to the procreation of human life. 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.So we are given here the two foundational assertions:
- Children are not an optional attachment to a marriage (an add-on, you might say) but rather are a natural result and philosophical aim of marital love.
- God, in designing marriage, established a strong connection between the unitive significance of marriage (a man and a woman coming together as a couple) and the procreative significance of marriage (the capability to produce offspring). In other words, just as it is immoral for us to break that bond between a man and a woman established in marriage, so it is also immoral for us to separate the act of marriage from the possibility of producing new life.
Married couples should regard it as their proper mission to transmit human life and to educate their children. . .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.So, in fact, this view is not opposed to the idea of regulating procreation. That is, provided that 1) the method of regulation is only that which is naturally built in to us (for example, to leverage periods of natural infertility) and 2) the goal is not to avoid having children, but rather to have children in a responsible manner.
But is not birth control a method of regulation? Why then the prohibition?
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. 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:
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.The difference, then, between natural methods of regulation and actually contraception is that the natural methods are not meant to eliminate entirely the possibility of procreation. One might say, the couple that employs contraceptive tools are enjoying the sexual benefits of the marriage, but they are unwilling to cooperate with God and give him the opportunity to create life from that union.
Furthermore, such a couple fails to accept the premise, described earlier, that children are the natural and ultimate fruit of the love exchanged between husband and wife. And so, in a certain sense, they are falling short of the fullest expression of their love for each other.
Now, I believe this view deserves additional biblical and logical scrutiny, both in its foundational premises, and in the conclusions it draws from them. But I hope that I have represented it accurately. This is the highest view of marriage and procreation that I have encountered, and also the most beautiful.

