Responsible parenthood also and above all implies a more profound relationship to the objective moral order established by God, of which a right conscience is the faithful interpreter. The responsible exercise of parenthood implies, therefore, that husband and wife recognize fully their own duties towards God, towards themselves, towards the family and towards society, in a correct hierarchy of values.

In the task of transmitting life, therefore, they are not free to proceed completely at will, as if they could determine in a wholly autonomous way the honest path to follow; but they must conform their activity to the creative intention of God, expressed in the very nature of marriage and of its acts, and manifested by the constant teaching of the Church." (10)
 

Respect for the Nature and Purpose of the Marriage Act

11. These acts, by which husband and wife are united in chaste intimacy, and by means of which human life is transmitted, are, as the council recalled, "noble and worthy," (11) and they do not cease to be lawful if, for causes independent of the will of husband and wife, they are foreseen to be infecund, since they always remain ordained towards expressing and consolidating their union. In fact, as experience bears witness, not every conjugal act is followed by a new life. God has wisely disposed natural laws and rhythms of fecundity which, of themselves, cause a separation in the succession of births. Nonetheless the Church, calling men back to the observance of the norms of the natural law, as interpreted by its constant doctrine teaches that each and every marriage act (quilibet matrimonii usus) must remain open to the transmission of life. (12)
 

Two Inseparable Aspects: Union and Procreation

12. That teaching, often set forth by the magisterium, is founded upon the inseparable connection, willed by God and unable to be broken by man on his own initiative, between the two meanings of the conjugal act: the unitive meaning and the procreative meaning. Indeed, by its intimate structure, the conjugal act, while most closely uniting husband and wife, capacitates them for the generation of new lives, according to laws inscribed in the very being of man and of woman. 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 ordination towards man's most high calling to parenthood. We believe that the men of our day are particularly capable of seizing the deeply reasonable and human character of this fundamental principle.