On the Contrary, the Church finds inerrancy in Her Scriptures, Her Traditions, Her Councils, and the Ex-Cathedra teachings of the Vicar of Christ, the Supreme Pontiff, as they concern faith and morals. The Church, however, concerning these four realms, has been absolutely silent about contraception, so Her teaching on contraception cannot be considered infallible.
I answer that, what is meant by “contraception” is a method invented by man in order to reduce the chances of pregnancy. It is agreed, and could not be denied, that the Church has taught infallibly that sexual acts are intended for the sake of producing children, and that an act divorced from its end is immoral, but though these principles have been established infallibly, the intended conclusion has not. As is shown later, this is because contraception is a matter of discipline. But if it were a matter of faith and morals, it would be considered infallible if declared as such.
The closest any two Church authorities come to declare such infallibility are the Council of Nicea and the document Humanae Vitae. Though the document Humanae Vitae is not an ex-cathedra teaching, its strongest statement concerning inerrancy does not actually make the direct claim that this church teaching is inerrant. “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.” (Vademecum for Confessors 2:4, Feb. 12, 1997). Yet this passage does not say “This teaching is definitively or irreformably held to be definitive and irreformable”, or, more succinctly, “This teaching is definitively and irreformably held”. As such, Humanae Vitae is not claiming an inerrant teaching, but rather claiming the Pontiff’s believe that there exists an inerrant teaching; a belief that should be respected, but is in no wise definitive, or irreformable.
Secondly, we consider the Nicean council’s statement: “If anyone in sound health has castrated himself, it behooves that such a one, if enrolled among the clergy, should cease [from his ministry], and that from henceforth no such person should be promoted.” (Canon 1, Nicea). This is speaking about permanent castration, which would be a clear defilement of the body, and though this is still a disciplinary teaching, as will be shown below, it is in no wise an escapable teaching. However, as this only touches tangentially, to show that contraception as above defined can be used in an immoral way, it has no bearing on the argument.
Reply Obj. 1 has been addressed sufficiently in the answer.
Reply Obj. 2 is ambiguous, as there are different scholars all the way back to Rashi, and the Talmud itself declares that “a man may do with his wife as he wishes” (Nedarim 20a; Pesachim 112b), so long as he fulfills the marriage contract and does not spill his sperm outside the woman’s body. Also, halakhah holds that any sexual act that does not involve sh’chatat zerah (spilling sperm outside the body), including birth control, is permissible. As there are open interpretations of this scripture, and the magesterium has not definitively declared, as a matter of faith, what this scripture is supposed to indicate, it cannot be considered an infallible teaching.
Reply Obj. 3 All teachings of the Church Fathers that are considered definitive within Sacred Tradition are supported by the Magesterium, the supreme authority in interpreting Sacred Tradition. As the Church has not offered a definitive interpretation of this within an Ecumenical Council, or an ex-cathedra statement, we cannot yet completely (infallibly) agree as to what has been shown by Sacred Tradition, concerning the Church Fathers, and dealing with contraception above defined.
Reply Obj. 4 Human reason, however, can at times be true, and at other times untrue, as it depends primarily on the senses. The case of contraception is even more ambiguous, as the physical effects entail effects on the soul. Such an ambiguity involves abstraction, and if such abstraction within reason does not rest on divinely revealed and infallible truths from the Sacred Doctrine, they can only be argued to be likely, and so cannot be considered infallible themselves.