But sexual pleasure within marriage becomes unnatural, and even harmful to the spouses, when it is used in a way that deliberately excludes the basic purpose of sex, which is procreation. In some centuries, even condoms were used (though made out of animal skin rather than latex).
God’s gift of the sex act, along with its pleasure and intimacy, must not be abused by deliberately frustrating its natural end—procreation. The Bible mentions at least one form of contraception specifically and condemns it.
This teaching is to be held as definitive and irreformable.
Contraception is gravely opposed to marital chastity, it is contrary to the good of the transmission of life (the procreative.aspect of matrimony), and to the reciprocal self-giving of the spouses (the unitive.aspect of matrimony); it harms true love and denies the sovereign role of God in the transmission of human life" (Pope Paul VI predicted grave consequences that would arise from the widespread and unrestrained use of contraception.
Let them consider, first of all, how wide and easy a road would thus be opened up towards conjugal infidelity and the general lowering of morality.In 1968, Pope Paul VI issued his landmark encyclical letter Humanae Vitae (Latin, "Human Life"), which reemphasized the Church’s constant teaching that it is always intrinsically wrong to use contraception to prevent new human beings from coming into existence.Contraception is "any action which, either in anticipation of the conjugal act [sexual intercourse], 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" (Humanae Vitae 14).But, as it is evident that this is said of those who willfully do the thing and presume to castrate themselves, so if any have been made eunuchs by barbarians, or by their masters, and should otherwise be found worthy, such men this canon admits to the clergy" (Canon 1). Observe, the thing which he [Onan] did displeased the Lord—and it is to be feared; thousands, especially of single persons, by this very thing, still displease the Lord, and destroy their own souls." (These passages are quoted in Charles D.Augustine wrote in 419, "I am supposing, then, although you are not lying [with your wife] for the sake of procreating offspring, you are not for the sake of lust obstructing their procreation by an evil prayer or an evil deed. For Onan goes in to her; that is, he lies with her and copulates, and when it comes to the point of insemination, spills the semen, lest the woman conceive. Provan, , Pope Paul VI stated, "[W]e must once again declare that the direct interruption of the generative process already begun, and, above all, directly willed and procured abortion, even if for therapeutic reasons, are to be absolutely excluded as licit means of regulating birth.