Doctor,I though I'd start thsi by bringing up the relevant passage from Humanae Vitae which deals with the matter in question:
This is off topic, but I want your thoughts on this. You've talked about the purpose of sex before on this blog, and after mulling on it for a while, a thought occurred to me.
If I remember correctly, there are supposed to be two parts to sex, the unitive and the procreative. What if the primary purpose of sex is actually the unitive part,and the procreative part is a secondary purpose?
These are half formed thoughts, but critiques are welcome.
The sexual activity, in which husband and wife are intimately and chastely united with one another, through which human life is transmitted, is, as the recent Council recalled, "noble and worthy.'' It does not, moreover, cease to be legitimate even when, for reasons independent of their will, it is foreseen to be infertile. For its natural adaptation to the expression and strengthening of the union of husband and wife is not thereby suppressed. The fact is, as experience shows, that new life is not the result of each and every act of sexual intercourse. God has wisely ordered laws of nature and the incidence of fertility in such a way that successive births are already naturally spaced through the inherent operation of these laws. The Church, nevertheless, in urging men to the observance of the precepts of the natural law, which it interprets by its constant doctrine, teaches that each and every marital act must of necessity retain its intrinsic relationship to the procreation of human life.[ED]If we look at the female menstrual cycle, we notice that the potential for fertility is not present throughout the cycle but is limited instead to about six days.
In other words, in an "average" 28 day cycle, there is no potential for procreation in roughly 22 of the 28 days present. Sexual activity during this period has no "intrinsic relationship to the procreation of human life." This is not my opinion, it is an empirically observable fact, like the Earth's rotation around the Sun.
The fact that for most of the menstrual cycle sexual activity is intrinsically infertile has several important implications:
Firstly, what exactly is sex for? Clearly that assertion, carried over from Aristotle, that sex is primarily for procreation is wrong given that most sexual acts occur outside the fertility window. As I see it, sex is teleologically ordered towards getting people together, i.e. it is primarily unitive. The generation of life is a second order phenomenon which occurs after union. In fact, this second order phenomenon is completely outside the couple's control. If you look at the above graph, the probability for fertility is only about 35% when sex activity deliberately occurs at the optimal point in the menstrual cycle. Even in healthy people sex at the optimal time is still not "intrinsically" linked to fertility.
Secondly: Given that the unitive meaning seems to be the primary reason for sexual activity does that mean that all acts of infertile sex are legitimate. In my opinion acts which private the sexual act are acts which are contra Caritas and are therefore forbidden. The difficulty here is determining what constitutes a privation.
For instance, does a using a condom during the infertile phase of the cycle constitute a privation?
The old "manualist" theologians, divided the sexual act into voluntary and physiological components.
The sexual act was understood as depositing the sperm into the vagina, the physiological component took care of the fertilisation. Taking a holistic view with regard to Church tradition and the notion of privation, it's my opinion that privation of sexual act consists of measures which aim to frustrate the deposition of live semen into the vagina. That means things like condoms, pessaries, caps, spermicides are morally illicit.
Actions which mutilate the reproductive tract, vasectomy and tubal ligations are likewise illicit.
However, the gravity of the sin in these circumstances needs to be evaluated in the context of weighing the unitive good vs the procreative good should they come into opposition for whatever reason. Suppose a couple are too poor to afford contraception and already have six children and don't want anymore. A U.S. government sponsored program is offering free sterilizations. I know it's wrong but I don't know if it's mortal given the new evaluative context. I don't have a firm position on this.
What's interesting is the Pill and other anovulants. The aim here is to induce a state in the woman that is akin to the infertile phase of the menstrual cycle and therefore such agents should prima facie be licit. The question here does the suppression of ovulation in itself constitute a privation in fertility. Strictly speaking, it does constitute a privation of the periodicity of fertility, though it does not constitute a privation in fertility per se. As women who take the pill return to their previous fertility once stopping it. What the pill does is modulate fertility, not abolish it.
The thing is that the Catholic Church does permit the use of the pill provided that it used for the treatment of a medical condition, once again from HV:
On the other hand, the Church does not consider at all illicit the use of those therapeutic means necessary to cure bodily diseases, even if a foreseeable impediment to procreation should result there from—provided such impediment is not directly intended for any motive whatsoever.This bit of text is actually quite problematic. Here the Church is permitting the use of Pill based on the principle of double effect. But the whole point of double effect doctrine is that the benefit of the intended effect is greater that privation of the unintended one. What that means is that, as a treating physician, I have to "weigh" the benefit of the therapeutic affect against the trade off in fertility. The Pill, for instance, is quite effective at dysfunctional uterine bleeding. Is the treatment of heavy periods worth the loss of fertility? The Church seems to think it's OK. It also works well for acne. I mean is the treatment of it of more gravity than the loss of fertility. Clearly, according to the Church, acne seems to be a more serious condition than the loss of fertility. Go figure? This is one of the reasons why I reckon the document is a mess and it's why I started thinking that maybe the laity's rejection of it may have had deeper origins than just simple rebellion to Church teaching.
However, what most people don't know is that the Church actually does permit the suppression of ovulation for the regulation of fertility through the Lactation Amenorrhea Method. The Church is quite OK with the use of an endogenous anovulant, though it's not happy with an exogenous one. Once again, go figure? However, all things considered, it would appear that the Church has unintentionally permitted the regulation of fertility provided there is a good reason.
Summing up, I think an evaluation of coitus in the the light of empirically demonstrable data leads to the conclusion the primary end of coitus is unitive with procreation being a secondary end. This view is much more in alignment with human nature and common sense than the traditional view. A view which I feel was strongly influenced by a Manichean bias in early Christianity which saw no good in Eros, even within marriage.
The Teleology of Coitus.
A Slow Toxin. Natural Law and Tradition
A slightly bigger if less accurate study on the fertility window.