In this post, a Catholic blogger attempts to define the "serious reasons" which allow for the use of periodic continence (NFP) within marriage.
My comment follows:
Because the "Church" never defined "serious reasons", it was left to us to fill in the blank, and apparently this is an attempt to fill in the blank. And even with this attempt, the author implies that our attempt to fill in said blanks will fall short without the guidance of a "solid spiritual director versed in these matters." Well good luck finding one of those. But beyond that, let's examine a few things:
The author says that artificial contraception is "intrinsically evil because they (condoms, pills) intervene in the natural process", but periodic continence is "morally neutral." I would argue that condoms and pills are not intrinsically evil things because they are things. Their use becomes problematic when they are employed with an evil intent: to prevent conception.
Likewise, periodic continence becomes problematic when it is employed with an evil intent: to prevent conception without "serious reason.". In fact, periodic continence, since it is an act of the will (I will not have sex with my spouse), is NEVER morally neutral. It can be morally good or morally evil, but it is never neutral.
I also find it curious that the central moral dilemma of modern man - the control of procreation (let's face it) was addressed by our Church via a pope in what appears to be a sidebar to an already obscure address to an even more obscure group (Italian midwives).
One could argue that the moral application of periodic continence had been addressed earlier in more prominent addresses by Pius XI (Casti Connubii) and later by Paul VI (Humanae Vitae), but both encyclicals do not enumerate the "reasons", as does Pius XII, who in fact provides the grounds for the morality of the method.
JPII gets into it in his Theology of the Body, but TOB is way down there on the scale of authoritative pronouncements.
Thus, we are apparently left with a scramble to unpack the four reasons left us by Pius XII in a tiny address that carries relatively little magisterial weight.
Actually, the Catechism rescues us by its use of the word "just" as in "just cause". However, I've yet to read or hear any attempt to unpack this, so let me give it a go.
When the Church uses "just" relative to moral issues it generally does not mean "just figure it out for yourself". The best parallel would be the use of the word "just" in defining "just war".
There are several key provisions which must be in place for a war effort to be considered "just" and therefore morally "inbounds". One of the key provisions for a Just War is "proportionality": the benefits must equal the damage.
Denying God souls to love (children) - by whatever means - is serious business and demands proportionate (just) cause. And when it comes to marital relations the discernment of that cause cannot be reliant on a list, or anyone's attempt to define that list - which is probably why no pope ever has.
Personal holiness is your only aid in this regard. Total submission to the Holy Spirit and union with God in and through his sacraments is all there is. Throw away your charts and get out your rosaries.
Disclaimer: Father of eleven who thought one was enough and is so glad things did not go as I planned.