Pope Celestine’s error was due to a misinterpretation of the Pauline Privilege (1 Cor. 7:15), which permits the bond of a natural marriage – i.e., a true marriage by spouses who are not baptized – to be dissolved if one of the spouses becomes a believer and is then abandoned by the unbeliever. By failing to properly distinguish between a natural vis-à-vis a sacramental marriage, Celestine misinterpreted these words of Scripture as meaning that a valid sacramental marriage – i.e., one entered into by two persons who were both baptized – will be dissolved if one of the spouses falls into heresy. Celestine’s immediate successor, Pope Innocent III, corrected the error in the letter Quanto te Magis, addressed to the bishop of Ferrara. Wrote Pope Innocent:
Your brotherhood has announced that with one of the spouses passing over to heresy the one who is left desires to rush into second vows and to procreate children, and you have thought that we ought to be consulted through your letter as to whether this can be done under the law. We, therefore, responding to your inquiry regarding the common advice of our brothers make a distinction, although indeed our predecessor [Celestine III] seems to have thought otherwise, [the distinction being] whether of two unbelievers one is converted to the Catholic Faith, or of two believers one lapses into heresy or falls into the error of paganism.
If one of the unbelieving spouses is converted to the Catholic faith, while the other either is by no means willing to live with him or at least not without blaspheming the divine name, or so as to drag him into mortal sin, the one who is left, if he wishes, will pass over to second vows. And in this case we understand what the Apostle [Paul] says: "If the unbeliever depart, let him depart: for the brother or sister is not subject to servitude in (cases) of this kind" (1 Cor. 7:15). And likewise (we understand) the canon in which it is said that "insult to the Creator dissolves the law of marriage for him who is left” (Contumelia creatoris solvit jus matrimonii circa eum qui relinquitur).
But if one of the believing spouses either slips into heresy or lapse into the error of paganism, we do not believe that in this case he who is left, as long as the other is living, can enter into a second marriage. (…) Although indeed true matrimony exists between unbelievers [i.e. a natural marriage], yet it is not ratified; between believers, however, a true and ratified marriage exists, because the sacrament of faith [i.e., baptism], which once was admitted, is never lost, but makes the sacrament of marriage ratified so that it itself lasts between married persons as long as the sacrament of faith endures.
Pope Innocent correctly interpreted the words of St. Paul (1 Cor. 7:15) as being applicable to a natural marriage bond of two unbelievers (which can be dissolved in certain circumstances), rather than a sacramental marriage bond which remains until death do them part.
The erroneous judgment of Pope Celestine highlights the limitations of papal infallibility by showing that a true Pope can, as part of his teaching office (Magisterium), render a judgment that contradicts divine revelation and confirms a person in objective mortal sin. Such a thing is possible provided the Pope is not exercising his Magisterium in an extraordinary manner by (1) issuing a final and definitive judgment (2) concerning a matter of faith or morals (3) to be held by the universal Church. If these conditions are not met, error – even serious error – is possible. And if anyone believes that all non-infallible judgments of a Pope must at least be “infallibly safe” (even if not infallibly true), they will have a difficult time explaining this one, since this non-infallible papal judgment confirmed a woman in the objective state of adultery.
But there is more to this case, which further demonstrates the limits of infallibility and shows us what God can permit in his Church.
Celestine’s Error Incorporated into Canon Law
The limitations of Papal Infallibility is further highlighted by the fact that the error of Pope Celestine was later included in the Decretals of Pope Gregory IX (known as Quinque Libri Decretalium), which was the first collection of Canon Law promulgated by a Pope for the universal Church.
In his well-known commentary on the 1917 Code, Fr. Charles Augustine, O.S.B., explains that the Papal Bull of Gregory IX, Rex Pacificus, which promulgated the Decretals, gave “full juridical value as a law text” to “each and every chapter in its dispositive part” which obviously includes the erroneous teaching of Pope Celestine. The Decretals of Gregory were later included in the Corpus Iuris Canonici (“Body of Canon Law”), which remained in force until the promulgation of the 1917 Code.
Here is the text containing Pope Celestine’s error, taken from the Decretals of Pope Gregory as found in the Corpus Iuris Canonici:
Decretals of Gregory IX, Lib. III, Tit. XXXII, Laudabilem, ‘On the conversion of the infidels,’ by Pope Celestine III:
A Christian man denied Christ out of hatred for his wife and united himself to pagan woman, with whom he procreated children. The Christian woman, who had been abandoned unto the dishonor of Jesus Christ, went into a second marriage with the assent of the Archdeacon and had children. It does not seem to us that if the first husband returns to the unity of the Church she ought to depart from the second and go back to the first, especially since she was seen to have departed from him by the judgment of the Church. And, as St. Gregory [the Great] testifies, ‘the affront to the Creator dissolves the right of marriage (solvat ius matrimonii) for the one who is left out of hatred of the Christian faith’. (…) [Concerning this question we have] the rule and the doctrine of the Apostle, by which it is said "if the infidel depart, let him depart. For a brother or sister is not under servitude in such cases" (1 Cor. 7:15 – i.e., the Pauline Privilege), as well as the famous decree of Gregory [found in the Decretum of Gratian]: ‘it is not a sin if [the spouse], having been dismissed for God's sake, joins another; the departing infidel [however], has sinned and against God and against matrimony’.”
Commenting on the case of Celestine and the above citations specifically, Bellarmine wrote:
The thirty-third [Pope accused of heresy] is Celestine III, whom Alphonsus de Castro asserted could not be excused of heresy in any way because he taught that Matrimony could be dissolved by heresy, and that it would be lawful for one to enter into another marriage when his prior spouse had fallen into heresy. Even if this decree of Celestine were not extant, still it was formally in ancient Decretals, the chapter, Laudabilem, ‘On the conversion of infidels,’ which is the decree Aphonsus says that he saw. Moreover, that this teaching of Celestine is heretical is clear, because Innocent III (Cap. “Quanto,” c. 3) taught the contrary on Divorce and the Council of Trent also defined the same thing.
Bellarmine goes on to defend Pope Celestine from the accusation of heresy by essentially arguing that the matter had not yet been solemnly defined (“the whole matter was still being thought out”) and by noting that Celestine did not intend for his erroneous judgment to be an ex-cathedra definition (he “responded with what seemed more probable”). While that may excuse Celestine from heresy properly so-called, and demonstrate that he did not violate Papal infallibility, what this historical case does show is that a Pope can commit a serious error in judgment concerning a moral issue (one that should have been clear) as long as he does not intend for his judgment to be a solemn definition. This case also shows that a very serious papal error, contrary to divine law, can be incorporated into Canon Law and promulgated by a Pope, with the force of law,  for the universal Church.
Now, for those Sedevacantists who say it is “impossible” for errors to come from the Church (“the Church cannot give evil”), I ask: Do you deny that the error of Pope Celestine is evil, or do you deny that the evil teaching, which originated from one Pope and was promulgated into Canon Law by another, came from the Church? And if it didn’t come from the Church, from whence did it come?
This historical case serves as important precedent for our day by showing us several things:
1. The Church’s infallibility is limited to dogmatic definitions, or to revealed truths that have been definitively proposed by the force of the ordinary and universal Magisterium, with the latter requiring both a synchronic universality (universality in space) and also diachronic universality (universality in time).
2. If a doctrine has not been solemnly defined, or if the teaching in question is novel (not consistent with what the Church has always taught), there is no divine guarantee that it will be free from serious error.
3. It is possible for a Pope to render an erroneous judgment, based on a misinterpretation of Scripture, which confirms a person in the state of objective mortal sin.
4. Not all judgments of the Pope concerning Faith or morals are infallibly true, nor are they always infallibly safe - unless one’s definition of “infallibly safe” covers teachings that are contrary to divine law and lead to objective mortal sinThis historical case also shows us that it is within the realm of possibility for a serious error to be incorporated into Canon Law and promulgated for the universal Church by a true Pope.
All four of these points are important to keep in mind during our day, lest we err in our own judgment by believing that certain things which God, in His Wisdom, has chosen to permit (for a greater good) are “impossible” and end by losing the Faith in the Church Herself.
This article appeared in a recent Print/E-edition of The Remnant. To see what else you missed:
 Alphonsus de Castro, First Book Against the Heresies (1565), ch. 4.
 Decretum of Gratian, Secunda Pars. Causa XXVIII. Quaet. II, c. 2
 Pope Innocent III, Quanto te Magi, to Hugo, Bishop of Ferrara, May 1, 1199, Denz. 405-406.
 “From its promulgation by Pope Gregory IX in September 1234, until the Pio-Benedictine Code came into full force in May 1918, the Quinque Libri Decretalium was the basic canon law of the Catholic Church. An authoritative collection—not a code—of canons, the … books were divided into 185 ‘titles’, themselves made up of 1,871 ‘chapters’.” (Dr. Edward Peters, Resources on Ius Decretalium, Friedberg Edition, January 3, 2013. Source: www.canonlaw.info).
 “The next important phase of canonistic development began in 1234 when Gregory IX promulgated a systematic collection of all the decretals and canons … which he wished to be preserved as laws of universal validity” (Tierney, Brian, The Foundations of the Conciliar Theory, Catholic University of America, Washington, DC, 1955, p. 17). “The reason for this collection [i.e., Decretals of Gregory IX] is stated in the Bull ‘Rex pacificus’ [in which the Pope promulgated the laws] as follows: Some decretals, on account of their length and resemblance to each other, appeared to cause confusion and uncertainty in the schools as well as courts, and to remedy this evil, the present collection is issued as an authentic one, to be employed in schools and ecclesiastic courts exclusively of all others. This meant that (a) the former five compilations were henceforward destitute of juridical value, and therefore could not be alleged as law-texts by the ecclesiastical judges; (b) each and every chapter in its dispositive part, no matter what its source or authority, was to have full juridical value as a law-text; (c) the collection was to be considered the Code of Law for the universal (Latin) Church, to the exclusion of all others of a general character.” (Augustine, Charles, OSB Commentary on the New Code of Canon Law, vol I, 2nd ed, (Herder Book Co, St. Louis Mo., London, 1918) Pp. 36-37.
 “Sometime in the year 1230, (St.) Raymond Peñafort began compiling the texts that would eventually comprise Pope Gregory IX's famous Quinque Libri Decretalium. Upon its promulgation in September of 1234 as the Church's first authentic collection of canon law (not yet a Code, but a binding collection nonetheless), the Liber Extra (as the QLD was also known) was the mechanism by which the canon law of the Catholic Church functioned for nearly 685 years, that is, until the Pio-Benedictine Code went into full effect in 1918” (Dr. Edward Peters blog, In The Light of the Law, January 21, 2010).
 "Si infidelis discedit odio Christianae fidei, discedat. Non est enim frater aut soror subiectus seruituti in huiusmodi. Non est enim peccatum dimisso propter Deum, si alii se copulauerit. Contumelia quippe creatoris soluit ius matrimonii circa eum, qui relinquitur. Infidelis autem discedens et in Deum peccat, et in matrimonium…” (Gratiana, Secunda Pars. Causa XXVIII. Quaet. II, c. 2).
 Corpus Iuris Canonici - Volume 2, Decretal. Gregory IX, Lib. III, Tit. XXXII, “Concerning the Conversion of the infidels,” Cap. 1, pp. 587-588
 Bellarmine, De Romano Pontifice, bk. 4, ch XIV.
 “In 1230 Gregory IX ordered St. Raymund of Peñafort to make a new collection, which is called the "Decretals of Gregory IX". To this collection he gave force of law by the Bull "Rex Pacificus", 5 Sept., 1234” (Original Catholic Encyclopedia, 1913, Vol. IX, p. 393).
 For a revealed truth to be proposed infallibly by the force of the ordinary and universal Magisterium, the doctrine must possess a definitive character, which is known, not by a single definitive act, but by a multitude of non-definitive acts. A doctrine, for example, which has always been taught and practiced (e.g., that only men can be ordained to the priesthood) I a doctrine that is considered to possess a definitive character, even though it has never been solemnly defined. The doctrine must also be universal in the full sense of the word, which requires that it be taught by the entire body of bishops (universal in space), and it must extend back to Apostolic Age, at least implicitly (universal in time). This latter point is clear from the letter of Pius IX, Tuas Labentur, in which he says “Even in the matter of that subjection which must be given in the act of divine faith, it should still not be restricted to those things that have been [solemnly] defined in the obvious degrees of the Oecumenical Councils or by the Roman Pontiffs of this See, but must also be extended to that which is taught as divinely revealed by the ordinary Magisterium of the entire Church spread throughout the world [universally in space], and which, as a result, is presented as belonging to the faith according to the universal and constant consensus (universali et constanti consensus) [universally in time] of the Catholic theologians.” (Tuas Libenter, English translation published in The Catholic Church and Salvation, by J. Fenton, Seminary Press, New York, 2006, p. 4). The Sedevacantist apologists who reject the diachronic universality almost always cut the above quotation short immediately after the words “spread throughout the world”, thereby eliminating the portion of Pius IX’s teaching that reject. See, for example, John Daly’s Article, “Did Vatican II Teach Infallibly” in which the quotation form Tuas Libentur is cut short each and every time he cites it.