• NFP merely observes natural cycles, unlike artificial contraception which actively obstructs them. Therefore, it works with nature.
• The Sacred Penitentiary in the 1800s and Pius XII in the 1950s allegedly allow NFP – therefore, it is a traditional practice, with evidence of long-standing acceptance.
• The „unitive‟ and „procreative‟ meanings or significances of the marital act are inseparable, according to modern theology. NFP supposedly respects both, allowing couples to express unity even when avoiding procreation.
• NFP requires communication and discipline, which are virtues strengthening the marriage.
• Couples should „discern‟ their family size based on their conditions, using NFP as the tool for this discernment.

These arguments, however well-intentioned or widely repeated, fail to withstand scrutiny when measured against the immutable truths articulated in Casti Connubii and the broader Tradition.

All other goods are secondary and must be subordinated.

The Apostle himself is therefore a witness that marriage is for the sake of generation: „I wish,‟ he says, „young girls to marry.‟ And, as if someone said to him, „Why?‟, he immediately adds: „To bear children, to be mothers of families‟.

St. Augustine  — De bono coniug., cap. 24 n. 32

There is no co-equal „unitive‟ end in the essential structure of marriage according to this perennial teaching. Love is the context and ideal manner, but procreation is the defining purpose of the institution and the conjugal act itself.

Now, the sedevacantist Bishop Pivarunas (CMRI) argues that ‚NFP is not a deliberate frustration, as the timing of NFP cannot be perfect.’ While this statement holds partial truth, he makes no distinction between unintentional and intentional NFP. He completely ignores that it was definitely seen as sinful by the Sacred Penitentiary in the 1880s:

Q1: Whether married couples may have intercourse during such sterile periods without committing mortal or venial sin?

Q2: Whether the confessor may suggest such a procedure (NFP) either to the wife who detests the onanism of her husband but cannot correct him, or to either spouse who shrinks from having numerous children?

Fr. Le Conte, 1880

A: Married couples who use their marriage right in the aforesaid manner (note: regarding Q1) are not to be disturbed, and the confessor may suggest the opinion in question, cautiously, however, to those married people whom he has tried in vain by other means to dissuade from the detestable crime of onanism (note: regarding Q2).

Sacred Penitentiary, June 16, 1880

Note that the distinction here is the intention between Q1 and Q2: Intercourse during sterile periods in itself is not a sin, but intercourse during sterile periods specifically for the shrinking of the family, that is, to avoid conception (which equals contra-ception), is only tolerated (not approved) to avoid onanism, that is, masturbation.

If NFP was truly without sinfulness, why would the answer from the S.P. include terms such as „cautiously‟ and „to dissuade from onanism‟? There is absolutely zero „endorsement‟ here, only a toleration to prevent the worse sin of onanism, which Bishop Pivarunas completely misinterprets. He then cites the modernist Fr. Halligan (1917–1997) to support the claim that ‚NFP is lawful given sufficient reason,’ who in turn cites ‚common teaching of theologians’ for his justification:

Deliberately to limit the use of marital relations exclusively to the sterile periods in order to avoid conception (i.e., to practice periodic continence or rhythm) is, according to the common teaching of theologians, morally lawful in actual practice if there is mutual consent, sufficient reason and due safeguards against attendant dangers.

Fr. Halligan, cited by Bp. Pivarunas

Fr. Halligan is simply wrong here, as his teaching directly contradicts the answer given by the Sacred Penitentiary in 1853:

Q: Certain married couples, relying on the opinion of learned physicians, are convinced that there are several days each month in which conception cannot occur. Are those who do not use the marriage right except on such days to be disturbed, especially if they have legitimate reasons for abstaining from the conjugal act?”

A: Those spoken of in the request are not to be disturbed,

Sacred Apostolic Penitentiary, 1853

The latter half is the crucial distinction: Whether NFP done by accident or with the intention of limiting family size. Only the first one is not a sin: this is advised to calm the conscience of scrupulous couples who worry whether they’re sinning on certain days and not on others. However, it is not an endorsement of NFP and, even if it were considered one, it was superseded by the teaching of Pius XI later on.

Such wholesome instruction and religious training in regard to Christian marriage will be quite different from that exaggerated physiological education by means of which, in these times of ours, some reformers of married life make pretense of helping those joined in wedlock, laying much stress on these physiological matters, in which is learned rather the art of sinning in a subtle way than the virtue of living chastely.

Casti Conubii, 108

This „exaggerated physiological education‟ addresses intentional NFP directly: with its various methods, trackers, apps, etc. – all done with the intention of lust without consequences. Therefore, it is definitely a „subtle sin‟ to act as this modernist „Catholic‟ woman does – recalling her sadness about not being able to use contraception, but having to use NFP instead:

NFP (for avoiding pregnancy) is the complete opposite of a woman’s natural sex drive cycle. Basically I would not be able to have sex when I most want it [editorial note: on fertile days, women usually have a higher sex drive] and only be able to when I least want it.

[…]

After starting to track my cervical mucus, I felt a genuine wave of sadness come over me, like I am accepting a death sentence (to my sexuality), like I am pretending to want to do something I truly don’t.

„nfp‟ topic on r/Catholicism

Now, obviously she here complains from the modernist perspective, lamenting her inability to use regular contraception – but even she recognizes that it goes directly against her nature as a woman to only have relations on non-fertile days (in order to contracept).

This is the result of what you eventually end up with when practicing NFP: tracking mucus, Marquette method, temperatures, ovulation cycles, etc. – all of that effort in order to intentionally prevent God’s will – and Bishop Pivarunas still argues that this elaborate scheme is not a „deliberate frustration‟ and does not „impede contraception‟?

This simply flies in the face of Pius XI’s warning: whether the frustration is achieved chemically, mechanically, or chronologically is irrelevant to the intrinsic disordering of the act from its God-given end. Intentional NFP, as practiced above, is most definitely intentional contra-ception.

The softness on NFP by Pius XII (with his „grave reasons‟ justification) later on led to his successor Paul VI Paul VI facing great difficulty in justifying his teaching against contraception: if chronological contraception is allowed, then there is absolutely no moral difference to artificial contraception, since the intention is the same.

NFP substitutes scientific knowledge and technique for the virtue of chastity and trust in God’s Providence, it subtly shifts the focus from openness to God’s will regarding life to human control and calculation.

If such were their character from the beginning, they have not come together by wedlock but by debauchery. But if the two are not alike in such sin, I boldly declare either that the woman is, so to say, the husband’s harlot; or the man the wife’s adulterer.

St. Augustine  — De nupt. et concupisc., 17. cap. XV.

Prioritizing the physical union while actively thwarting its primary natural end is a form of „idolatry of the flesh‟ (CC, 107). The conjugal act is only „honest wedlock‟ when ordered primarily to offspring.

St. Augustine had already condemned the Manicheans for the same practice centuries earlier, although their reasoning was only slightly different (wanting to contracept since they saw the „Divine Light‟ being trapped in human flesh, which they taught, was imprisonment and inherently evil) - still, he foresaw their practice of observing cycles being rooted in passions:

Is it not you who hold that begetting children, by which souls are confined in flesh, is a greater sin than cohabitation? Is it not you who used to counsel us to observe as much as possible the time when a woman, after her purification, is most likely to conceive, and to abstain from cohabitation at that time, lest the soul should be entangled in flesh? This proves that you approve of having a wife, not for the procreation of children, but for the gratification of passion.

St. Augustine  — On the Morals of the Manicheans, ch. 18, p. 65

The idea that „using the Marquette method to avoid conception is traditional Catholic teaching‟ is simply untenable, at least since 388 AD – if Augustine and Pius XI would truly „allow NFP‟, why do they both write about continence as an alternative – and not : if a couple cannot contain themselves, they should simply „watch the days of the menses?‟ It is obvious that only licit and Catholic option is continence, not calculated avoidance, justified by out-of-context quotes from the 20th century that distort their original meaning.

Wherefore, let the faithful also be on their guard against the overrated independence of private judgment and that false autonomy of human reason. For it is quite foreign to everyone bearing the name of a Christian to trust his own mental powers with such pride as to agree only with those things which he can examine from their inner nature, […]

Casti Conubii, 104

Couples are told to „discern‟ based on subjective factors, effectively judging God’s revealed will („Increase and multiply‟) by their own circumstances and desires. This replaces trust in God’s „farseeing providence‟ (CC, 80) with human planning and control, a hallmark of modern pride.

„Love‟ or „unity‟ (undefined, subjective concepts) had to therefore be elevated to co-equal status, shifting marriage from an objective contract for rights ordered to a specific end (CC, 59) to a subjective covenant based on feelings:

These enemies of marriage go further, however, when they substitute for that true and solid love, which is the basis of conjugal happiness, a certain vague compatibility of temperament. This they call sympathy and assert that, since it is the only bond by which husband and wife are linked together, when it ceases the marriage is completely dissolved. What else is this than to build a house upon sand?

Pius XI  — Casti Conubii, 78

Notably, this heretical teaching is even espoused by the Eastern „Orthodox‟, see Are Annulments Catholic?.

Augustine goes even further, after condemning the Manicheans for their mistress-wives:

In marriage, as the marriage law declares, the man and woman come together for the procreation of children. Therefore whoever makes the procreation of children a greater sin than copulation, forbids marriage, and makes the woman not a wife, but a mistress, who for some gifts presented to her is joined to the man to gratify his passion.

Where there is a wife there must be marriage. But there is no marriage where motherhood is not in view; therefore neither is there a wife. In this way you forbid marriage.

St. Augustine  — On the Morals of the Manicheans, ch. 18, p. 65

If the essence of marriage is a subjective state of love or psychological compatibility, then its absence (or perceived absence) logically implies the marriage never truly existed in its essence. This subjective standard, enshrined in Canon 1095’s „lack of due discretion‟ (often interpreted as psychological incapacity for this ill-defined „union‟), is the direct cause of the annulment crisis.

The 338 annulments in the US in 1968 ballooning to over 27,000 by 2006 isn’t due to sudden mass psychological incompetence; it’s due to changing the legal definition of marriage to accommodate the NFP mindset. It creates the „disastrous ease of obtaining divorce‟ (or its functional equivalent, easy annulment) which Pius XI lamented:

Much more ought you, Venerable Brethren, […] by every fitting means, oppose […] that disastrous ease in obtaining divorce by an enduring love in the bond of marriage and by the inviolate pledge of fidelity given even to death.

Casti Conubii, 106

For if the man is the head, the woman is the heart, and as he occupies the chief place in ruling, so she may and ought to claim for herself the chief place in love.

Casti Conubii, 27

By making procreation optional and secondary, NFP provides the theological underpinning for the feminist rejection of traditional family roles. Whenever lust becomes primary, the woman, usually having less sexual drive and being in the „chief place of love‟, now holds the keys over the entire marriage, until it slowly erodes to a lustful debate about „rendering the obligation‟ and „living out one’s sexuality‟.

NFP facilitates this „false liberty and unnatural equality‟ that ultimately debases womanhood and destroys family order:

This, however, is not the true emancipation of woman, nor that rational and exalted liberty which belongs to the noble office of a Christian woman and wife […]

More than this, this false liberty and unnatural equality with the husband is to the detriment of the woman herself, for if the woman descends from her truly regal throne to which she has been raised within the walls of the home by means of the Gospel, she will soon be reduced to the old state of slavery (if not in appearance, certainly in reality) and become as amongst the pagans the mere instrument of man.

Casti Conubii, 75

But no reason, however grave, may be put forward by which anything intrinsically against nature may become conformable to nature and morally good.

Casti Conubii, 54

This single sentence obliterates the entire „grave reasons‟ framework introduced later by Pius XII (a framework itself problematic, shifting the basis from nature to a questionable „duty‟). If frustrating the act’s primary end is intrinsically against nature, no reason can make it morally licit.

The encyclical explicitly affirms that grace is always sufficient for spouses to remain chaste when necessary (CC 61):

There is no possible circumstance in which husband and wife cannot, strengthened by the grace of God, fulfill faithfully their duties and preserve in wedlock their chastity unspotted.

Casti Conubii, 61

Ironically, the idea that „we have to use NFP, it is not possible to contain ourselves otherwise‟ is put under anathema by the Council of Trent:

Let no one be so rash as to assert that which the Fathers of the Council have placed under anathema, namely, that there are precepts of God impossible for the just to observe. God does not ask the impossible, but by His commands, instructs you to do what you are able, to pray for what you are not able that He may help you.

Casti Conubii, 61

They will, in a great measure, turn and be turned away from these abominable opinions which to the dishonor of man’s dignity are now spread about in speech and in writing and collected under the title of „perfect marriage‟ and which indeed would make that perfect marriage nothing better than „depraved marriage‟, as it has been rightly and truly called.

Casti Conubii, 107

The widespread acceptance of NFP represents a profound crisis in the Church’s understanding of marriage. It is not a legitimate application of natural law but a subtle subversion of it, rooted in a modernist desire to accommodate worldly pressures and elevate subjective experience over divine ordinance. Casti Connubii remains the authoritative benchmark, exposing NFP as intrinsically disordered, historically unfounded in Church approval, and corrosive to the very fabric of marriage and family life.