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In the article “Making Babies: A Very Different Look at Natural Family Planning” H.W. Crocker defends Natural Family Planning as “the method which doesn’t work.”  He does have a point. Perhaps we Catholics place too much emphasis on how effective NFP is. Between the two, it is far better for us to “rejoice in the fallibility of NFP (that is, in the children who sneak past it)” than to forget that those very children are blessings from a generous God.
But we need not choose: there is an alternative more in line with God’s plan for rational creatures than either of these.
Practicing NFP is much like suspending judgment. There is a continence in the intellectual order which corresponds to continence in the physical order. For example, a young couple may find that repeated overdrafts have slowly brought them to the brink of financial ruin. If they are to avoid this, they cannot, must not, make another purchase beyond their means. Prudence requires that they now begin to scrutinize each purchase carefully, avoiding (withholding assent to) anything which will bring about the feared result. The principles governing such decisions apply also in decisions to have or not to have children.
One unfortunate by-product of NFP methods is that they focus much of our attention upon when to abstain. Yet, from a moral perspective, given a sufficient reason to use NFP, it is not abstaining from intercourse that requires justification, but intercourse itself. Much as the above couple must now justify each purchase, so a couple rightly using NFP must justify each marital act. In the order of prudence, abstention is the moral default. Assuming that “we must not now become a mother and father”, prudence demands that a couple refrain from sexual relations until they can be sure that having intercourse would be the right course of action for them.
In this light, the fallibility of NFP refers not so much to the failure of a method as to the weakness of moral persons. Given good reasons not to have one, a child’s “sneaking past” NFP practices, however much of a blessing it most certainly is in itself, may very well be evidence of human folly, imprudence, or moral weakness.
Someone might reply that we cannot be sure what will or will not happen. In particular, a couple can never be sure that a particular marital act will not result in new life, and so would be permitted under the circumstances.
Descartes, the mathematician-turned-philosopher, demanded a mathematical certitude for truth. Need a couple faced with this decision be that sure they will not conceive? That would set an impossibly high standard for human actions. For his part, Aristotle allowed for different degrees of certitude, mathematical and otherwise. If being sure can mean more than being mathematically sure, we ought to expect only that degree of certitude which is possible in our situation. We should not (and cannot) expect the certitude of mathematics when we draw conclusions about human actions, which are variable and subject to change.
To return to the couple practicing NFP, then, it comes down to the question: should we have relations on a given day? Given serious reasons to avoid a child at this time, prudence demands that we justify life-giving acts in the light of what we know. This cannot mean know in Descartes’ sense (for the conditions affecting fertility are many and varied), but in Aristotle’s sense: with a reasonable certainty. We should do all we can to justify marital acts before we decide to engage in them. Said negatively, if we are not sure, we ought, for now, to avoid an act which brings us out-of-line with God’s plan for us as rational creatures. (Again, abstention is the moral default.)
Someone may persist, asking whether even this lesser degree of certitude is possible: perhaps human sexuality is far too variable to allow for it. Perhaps we ought simply to admit the inadequacy of reason and rejoice in any children who “sneak past” our efforts to avoid conceiving them.
The problem with this account is that it misplaces blame. If prudence requires a couple to avoid having a child, their only moral recourse is abstention, unless they are sure that intercourse would have the same outcome (that they would not conceive). Without that assurance, however much they should rejoice in the child who “slips through”, they cannot, should not, rejoice in their own weakness. The fallibility of NFP thus turns out to be their own.
But further, and after all, human sexuality is not as variable as all that. Natural events are mostly regular: that’s what makes them natural. It is only reasonable to rely upon what commonly occurs, and our experience of the natural order is of something which happens in predictable ways. This is why proponents of NFP have good reason to speak of its effectiveness. The method is based upon nature, after all, and nature is nearly uniform. Women are not so different that they exhibit symptoms of fertility in altogether different (or even unique) ways. They tend to exhibit such things in the same way, and couples act reasonably in using such signs as a basis for prudent actions in married life.
What, then, of the exceptional cases? Even if we were to allow that symptoms of fertility occur with great regularity, surely there are women who cannot determine their fertility without even much ambiguity and imprecision?
First, admitting these as exceptions, we still would not rightly characterize NFP itself as a method which does not work. Second, even in such instances, it is not NFP which fails. Couples facing recourse to periodic abstinence must have serious reasons to do so. Prudence demands that they not have a child at this time. As we concluded above, then, it is not abstinence that requires justification, but intercourse. Absent sure signs that a child will not result, the couple must avoid relations. To do otherwise would be unreasonable. Ambiguities (in their case) arising from other sources notwithstanding, their positive duty in this regard is the same as anyone’s. In the language of suspending judgment, as they cannot reasonably expect to avoid conception, they should not consent to the act.
What, then, of couples who have “done everything right”? Who have judged the symptoms and acted as prudence requires, yet find themselves blessed with another child? Surely NFP has failed at least here.
Faced with this outcome, some have come to regard man’s judgment as being God’s judgment: they will not rejoice in the child that has “slipped through” their careful plans. They forget that God’s reason for things may very well exceed our ability to discover it. To such, NFP must have failed, for the result is a mistake, something contrary to human reason. Others, in an effort to avoid such presumption, end up by allowing reason no part whatsoever in these affairs. They will simply “let go, and let God”, forgetting that rational beings necessarily have a share in bringing God’s will about. And while reason itself acknowledges that we do not always discern God’s purpose, it is He who made us rational. This means we should rejoice in the great gift of a child, despite the possible inadequacies of our reason: for God Himself is not unreasonable, yet we may fail to see His purpose in things.
Focusing upon the fallibility or infallibility of NFP may distract us from a deeper issue: given our capacity to act against our better judgment, much of this problem may lie with us. Some may ignore what reason can know of the signs of human fertility, leaving them to rejoice in their children (as they most certainly ought) and in the “fallibility” of NFP (as they ought not). Others may have good reason to avoid conception yet fail to do so through simple weakness. It would be odd to rejoice in that weakness, however, as if it were the source of the goodness of God’s gift. While it is beyond dispute that children are God’s blessings howsoever they come to be, let us take care not to use that fact to justify what may very well be our own failings.
 Crisis, December 1, 2004
 Crisis, Letters to the Editor: H. W. Crocker III responds, February 3, 2005.
 Anyone familiar with contemporary Catholic family life knows that this is a highly contentious issue in itself. For example, see Thomas Storck’s article “NFP: A Defense and an Explanation” in the July 2006 edition of the Homiletic and Pastoral Review.
 A difficulty arises here, as a couple’s concluding that “we must not become a mother and father” appears to conflict with the requirement that sexual acts remain open to conception (“we may become a mother and father”). Karol Wojtyla noted and resolved this difficulty in Love and Responsibility, Chapter 4, “Periodic Continence: Method and Interpretation”.
 “From the point of view of the family, periodic continence as a method of regulating conception is permissible in so far as it does not conflict with a sincere disposition to procreate. There are, however, circumstances in which this disposition itself demands renunciation of procreation, and any further increase in the size of the family would be incompatible with parental duty. A man and a woman moved by true concern for the good of their family and a mature sense of responsibility for the birth, maintenance, and upbringing of their children, will then limit intercourse, and abstain from it in periods in which this might result in another pregnancy undesirable in the particular conditions of their married and family life.”” Karol Wojtyla, Love and Responsibility, trans. H.T. Willetts, San Francisco: Ignatius Press, 1981. Chapter 4, “Periodic Continence: Method and Interpretation”, p. 243.
 Failure in the use of NFP cannot be likened, say, to a torn condom, or to an ineffectively low dosage of contraceptive hormones. Here there is no technical fault, rather, conceiving a child can be directly traced back to the couple’s choice to have intercourse.
 Absent complete certainty, it is one thing to suspend one’s judgment utterly and another to do so within reason. René Descartes’ way of doing philosophy, for example, requires that one refrain from assenting to what he has not clearly and distinctly seen to be so. This insistence upon withholding assent famously leads Descartes down strange paths. Since he cannot prove that sensation is real, he must withhold his assent to what his senses have to say. In the end, Descartes is left with himself: I think, therefore I am, and it questionable whether he ever gets any further than this. An insistence upon such a standard for reason, then, seems to lead to an unreasonable outcome.
 To his credit, Descartes seems to have allowed for a less than a mathematical certitude in ethical matters, though it is difficult to see that this fits within his overall account of human knowledge and suspension of judgment. For Aristotle’s account, see Nicomachean Ethics, I.3.
 Prudence, which is numbered among the gifts God has given to married couples, is an intellectual as well as a moral virtue. To act imprudently is to act unreasonably, then, and so contrary to what God wills for his rational creatures.
 As Robert Bolt’s Thomas More observes: “God made the angels to show Him splendor—as he made animals for innocence and plants for their simplicity. But Man He made to serve him wittily, in the tangle of his mind.” St. Thomas Aquinas speaks of this peculiar distinction in his Treatise on Law, saying “among all others, the rational creature is subject to Divine providence in the most excellent way, in so far as it partakes of a share of providence, by being provident both for itself and for others.” Summa Theologiae, I-II, 91, 3, body.[/style]