In order to be moral, each and every sexual act must be procreative.
The primary end of marriage is the procreation and education of the offspring. This expression in Latin, generatio et educatio prolis, is used by Pope Pius XII in his well-known Address to Midwives.
Sexual acts are inherently ordered toward the good of procreation, for the sexual faculty is given by God to humanity first and foremost for that reason: procreation. The reciprocal gift of the spouses in enjoyment and delight is neither the exclusive nor the first good of the marital act. Whether or not a sexual act is enjoyable does not reveal whether or not that sexual act is moral. To be moral, each and every sexual act must be that type of act which is suitable in itself for the procreation of offspring, in order words, which is inherently directed toward procreation. For marriage, by its very nature, is ordered to the end of procreation as its primary good. Only sexual acts that are inherently ordered toward this end of procreation accomplish the primary good of marriage as the origin and source of new life. Therefore, each and every sexual act in a marriage must be open to the possibility of the procreation of children.
Contraceptive acts are inherently ordered toward the deprivation of the procreative meaning from sexual acts. Therefore, contraception has an evil moral object, and is intrinsically evil and always gravely immoral. Neither a good intention, nor dire circumstances, can transform an intrinsically evil act into an act that is moral or good or justifiable.
In order to be moral, each and every sexual act must be unitive.
God never intends a good end, such as procreation, by an immoral means. For a good end cannot justify an evil means. Therefore, the good end of procreation cannot be sought by artificial procreation, nor by the use of immoral sexual acts. The good end of procreation can only be sought by the good means of the union of husband and wife as one flesh. Both the unitive and procreative meanings must be found in each and every sexual act.
Pope Paul VI: “each and every marital act must of necessity retain its intrinsic relationship to the procreation of human life. This particular doctrine, often expounded by the magisterium of the Church, 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.” (Humanae Vitae, n. 12)
In order to be moral, each and every sexual act must be marital.
The magisterial teaching against procreation always states or implies that moral sexual acts take place only within marriage. For the Church has always definitively taught that sexual acts outside of marriage are intrinsically evil and always gravely immoral, including pre-marital sex, adultery, masturbation, and any other type of non-marital sexual act whatsoever.
Therefore, to be moral, each and every sexual act must retain a threefold good moral object which is marital, unitive, and procreative.
All non-marital sexual acts are intrinsically evil and always gravely immoral. All non-unitive sexual acts are intrinsically evil and always gravely immoral. All non-procreative sexual acts are intrinsically evil and always gravely immoral.
Contraception is intrinsically evil and always gravely immoral due to the deprivation of the procreative meaning in the moral object. Contraception is gravely immoral, regardless of whether or not the man and woman are married, because the presence or absence of the marital meaning does not change the fact that the sexual act is deprived of the procreative meaning. All sexual acts deprived of the procreative meaning are intrinsically evil, including contracepted acts in marriage, contracepted acts outside of marriage, masturbation, and all unnatural sexual acts between any persons, whether married or not.