Fairly frequently, one hears the following argument against the orthodox Catholic view that the use of marital[note 1] contraception is wrong: If Catholics were consistent, they would also prohibit Natural Family Planning (NFP), because there is no morally significant difference between NFP and contraception. One reason that this is a bad argument is that, as many authors have argued at length (here is my version), there really are significant differences between NFP and contraception, for instance grounded in the doing/permitting distinction.
But I think there is a simpler reason why this is a bad argument. For what is the conclusion of the argument? It is that if one rejects contraception, one should likewise reject NFP. Suppose that the argument succeeds in establishing this (it doesn't). Now the Catholic has to choose between two views:
- Marital contraception and NFP are both wrong.
- Marital contraception and NFP are both sometimes right.
The argument is a bad one for the following reason. The proponent of contraception believes that (a) marital contraception is sometimes right, and, presumably, that also (b) marital NFP is sometimes right. The well-informed orthodox Catholic denies (a) but accepts (b). But the argument, if it succeeds, will shift the well-informed orthodox Catholic to denying both (a) and (b). Nor will this shift affect much else in the orthodox Catholic's web of beliefs. While the teaching that contraception is wrong is interwoven with significant amounts of other Catholic beliefs, the teaching that NFP is right lacks that sort of interweave, simply because the teaching on NFP is of such recent date. Hence, the argument, if it succeeds, will increase disagreement. And surely that is not what the proponent of contraception wants. Indeed, since the proponent of contraception typically believes that unlimited reproduction is bad for people and the world, by offering the NFP-contraception argument to a well-informed orthodox Catholic, and thus convincing the orthodox Catholic that NFP is wrong, she is apt to contribute to the very problem she is trying to counter.
There is a general structure to this criticism. Suppose A believes p and q, and B believes p and not-q. A wishes to convince B of q. So A offers B the argument that p and not-q are logically inconsistent. This is not going to be a good argument if B's main reasons for holding not-q are much stronger than her main reasons for holding p, and if denying p does not force the denial of much else that B is committed to. If the argument succeeds in showing the inconsistency, it is more likely (at least if we limit ourselves to rational persuasion) to move B to believing not-p and not-q, which A believes is further from the truth.