Humanae Vitae is online at the Vatican site, and the text highlighted below is © Copyright – Libreria Editrice Vaticana.
24. Our next appeal is to (women and) men of science. These can “considerably advance the welfare of marriage and the family and also peace of conscience, if by pooling their efforts they strive to elucidate more thoroughly the conditions favorable to a proper regulation of births.” (See Gaudium et Spes 52) It is supremely desirable, and this was also the mind of Pius XII, that medical science should by the study of natural rhythms succeed in determining a sufficiently secure basis for the chaste limitation of offspring. (Address to Family Campaign and other family associations: AAS 43 (1951), 859) In this way scientists, especially those who are Catholics, will by their research establish the truth of the Church’s claim that “there can be no contradiction between two divine laws—that which governs the transmitting of life and that which governs the fostering of married love.” (See Gaudium et Spes 51)
Medical science does not really explore ways to assess fertility, does it? How much science has been added to NFP in the past half-century? Comments?