11 must be “ rightly understood ” and defines it in a way going far beyond a cursory or reductionist treatment focusing on the regulation of births . 33 First and foremost , responsible parenthood concerns “ an awareness of , and respect for , [ the ] proper functions of the body ’ s biological processes .” 34 Judging from its primacy in the text , it appears that the author wishes to highlight the relationship between the bio-physiological dimension of the human person and its importance as to the goods of marriage . This same emphasis is reiterated later in the document in its appeal to scientists , when it states that it is not only licit , but “ supremely desirable ” that medical science should engage in the study of the natural rhythms of fertility . 35 The text also gives scientific support to the Church ’ s claim regarding marriage as a reflection of the Trinity , in its unitive and procreative dimensions , i . e . that of love and life . Furthermore , the author of Humanae Vitae asserts that man , with the use of his intellect , has a duty and a right to control the biological functions of human fertility , and lauds the use of science — properly directed — in the pursuit of “ an activity in which a rational creature such as man is so closely associated with his Creator . ” 36 Here again , the Church speaks of sexuality and fertility as a united expression of the participation of man in the divine life .
St . John Paul II takes this praise of science to a more definitive level by insisting that knowledge of one ’ s fertility , especially in relation to married couples , is paramount to a proper living out of man ’ s dignity . He asserts :
33 Paul VI , Humanae Vitae , sec . 10 . 34 Ibid . 35 Ibid . sec . 24 . 36 Ibid ., sec . 16 .