*The Church also has affirmed that the illicitness of contraception is an infallible doctrine: “The Church has always taught the intrinsic evil of contraception, that is, of every marital act intentionally rendered unfruitful. 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” *(Vademecum for Confessors 2:4, Feb. 12, 1997).
Some history:
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Apostolic Tradition
The biblical teaching that birth control is wrong is found even more explicitly among the Church Fathers, who recognized the biblical and natural law principles underlying the condemnation… *
You say, “the biblical teaching that birth control is wrong” and still have provided no biblical teaching besides the rather ambiguous story about Onan from Genesis. Surely, such an important teaching which is the subject of countless threads here in CAF and is an area of major disagreement between millions of Catholics and the Church would have merited some mention somewhere in the books of the New Testament in a straightforward manner. And then in early church teaching before Augustine, there are only a handful of equally obscure passages including one by Barnabas about the wickedness of weasels. It’s not a very impressive demonstration of clear, widespread and constant Church teaching on this supposedly important issue.