Theo of the Body Question

The body, and the experience of the body, is the primal revelation of God which we encounter: we realize that there are "other people" out there, not under the control of our subjectivity yet acting very much as we act. From this we conclude that there are other people experiencing a life like that which we ourselves experience. In our relations with these people, we discover--in the experience of embodied sexuality--a hint of what it means to interact with another completely, in a very physical sense. This experience of self-gift to those "others" around us prepares us to understand the nature of a more complete gift of self, a spiritual nuptiality, which naturally arises from sexuality. And, as the Song of Songs shows us, this encounter with nuptiality teaches us about our proper relation to God--one of complete self-gift in body, soul, and spirit. With the advent of uniquely Christian revelation, we see that the lesson of nuptiality in fact describes the very inner relations of God Himself.

That's how it works. But, of course, we keep messing with it. There is marital congress which doesn't give rise to fruitfulness (that fruitful of children which mirrors the procession of Holy Spirit). We can manipulate this temporary infertility through timed abstinence, so as to significantly lessen the possibility of childbirth--NFP. Recently I was asked, "why is it OK to use astronomy to prevent childbirth, but not physics?" Why can we limit family size with calendars but not condoms?

Well, my answer was, essentially, that the good thing about NFP is that it doesn't work: there is always a chance that childbirth will result, and so therefore the parents are still open to life. Loving sacraments as I do, I think I was pre-disposed to think that this position was emminently rational: it's just like using mustum for Mass; the grape juice has almost no alcoholic content, but it's still OK to use because it has't been pastuerized and therefore turned irrevokably into grape juice--it might still be wine.

My audience was not similarly convinced. They pointed out that NFP is often promoted by Catholics as more effective than condoms. Certainly, NFP can be used with a contraceptive mentality alien to the "spirit of the no-contraception law."

Does anyone have a more articulate answer as to why having a big family, but occasionally using condoms (which may fail), is bad, while having a big family and just as frequently using NFP (which some claim is more effective) is OK?