This page has now an interesting history. If you read down, you will see the sequence of scholarly discovery, first in 1997 when a colleague brought new material to me, then in 2010, when a kindly and learned web-stranger brought still new material. The story grows more interesting and is well worth reading to the end.

The quotation seems to have gotten into circulation as something attributed to Augustine, and so I am asked the source. I cannot find the text in Augustine's own texts, nor does it sound Augustinian to me, but it is clearly popular. So I went on a web-crawl. To my surprise, delight, and then bemusement, I found that this quotation is a pan-denominational maxim, quoted as authoritative in a dizzying variety of incompatible Christian traditions. The closest I came to a source was Wesley, until I found a specific reference to John XXIII's first encyclical, Ad Petri cathedram of 1959. I cannot find the Latin text on-line, but the English translation is available, whence this quotation, its paragraph 72:

But the common saying, expressed in various ways and attributed to various authors, must be recalled with approval: in essentials, unity; in doubtful matters, liberty; in all things, charity.

I take that as suggesting that the Vatican's own scribes and scholars cannot find a sure attribution.

8 September 1997: Thanks to Prof. Gerald Schlabach of Bluffton College, I now have the following report, more than a century old, which gives the saying a seventeenth-century date:

Philip Schaff, History of the Christian Church, vol. 7, pp. 650-653 (repr. Eerdmans, Grand Rapids, 1965)

It was during the fiercest dogmatic controversies and the horrors of the Thirty Years' War, that a prophetic voice whispered to future generations tile watchword of Christian peacemakers, which was unheeded in a century of intolerance, and forgotten in a century of indifference, but resounds with increased force in a century of revival and re-union:

"IN ESSENTIALS UNITY, IN NON-ESSENTIALS LIBERTY, IN ALL THINGS CHARITY.

NOTE

On the Origin of the Sentence: "In necessariis unitas, in non-necessariis (or, dubiis) libertas, in utrisque (or, omnibus) caritas."

This famous motto of Christian Irenics, which I have slightly modified in the text, is often falsely attributed to St. Augustin (whose creed would not allow it, though his heart might have approved of it), but is of much later origin. It appears for the first time in Germany, A.D. 1627 and 1628, among peaceful divines of the Lutheran and German Reformed churches, and found a hearty welcome among moderate divines In England.

The authorship has recently been traced to RUPERTUS MELDENIUS an otherwise unknown divine, and author of a remarkable tract in which the sentence first occurs. He gave classical expression to the irenic sentiments of such divines as Calixtus of Helmstadt, David Pareus of Heidelberg, Crocius of Marburg, John Valentin Andreae of Wuerttemberg, John Arnd of Zelle, Georg Frank of Francfort-on-the-Oder, the brothers Bergius in Brandenburg, and of the indefatigable traveling evangelist of Christian union, John Dury, and Richard Baxter. The tract of Meldenius bears the title, Paraenesis votiva pro Pace Ecclesiae ad Theologos Augustanae Confessionis, Auctore Ruperto Meldenio Theologo, 62 pp. in 4to, without date and place of publication. It probably appeared in 1627 at Francfort-on-the-Oder, which was at that time the seat of theological moderation. Mr. C. R. Gillett (librarian of the Union Theological Seminary) informs me that the original copy, which he saw in Berlin, came from the University of Francfort-on-the-Oder after its transfer to Breslau.

Dr. Luecke republished the tract, in 1860, from a reprint in Pfeiffer's Variorum Auctorum Miscellanea Theologiae (Leipzig, 1736, pp. 136-258), as an appendix to his monograph on the subject (pp. 87-145). He afterwards compared it with a copy of the original edition in the Electoral library at Cassel. Another original copy was discovered by Dr. Klose in the city library of Hamburg (1858), and a third one by Dr. Briggs and Mr. Gillett in the royal library of Berlin (1887).

The author of this tract is an orthodox Lutheran, who was far from the idea of ecclesiastical union, but anxious for the peace of the church and zealous for practical scriptural piety in place of the dry and barren scholasticism of his time. He belongs, as Luecke says ("Stud. und Kritiken," 1851, p. 906), to the circle of "those noble, genial, and hearty evangelical divines, like John Arnd, Valentin Andrea,, and others, who deeply felt the awful misery of the fatherland, and especially the inner distractions of the church in their age, but who knew also and pointed out the way of salvation and peace." He was evidently a highly cultivated scholar, at home in Hebrew, Greek, and Latin, and in controversial theology. He excels in taste and style the forbidding literature of his age. He condemns the pharisaical hypocrisy, the philodoxia, philargia, and philoneikia of the theologians, and exhorts them first of all to humility and love. By too much controversy about the truth, we are in danger of losing the truth itself. Nimium altercando amittitur Veritas. "Many," he says, "contend for the corporal presence of Christ who have not Christ in their hearts." He sees no other way to concord than by rallying around the living Christ as the source of spiritual life. He dwells on the nature of God as love, and the prime duty of Christians to love one another, and comments on the seraphic chapter of Paul on charity (1 Cor. 13). He discusses the difference between necessaria and nonnecessaria. Necessary dogmas are, (1) articles of faith necessary to salvation; (2) articles derived from clear testimonies of the Bible; (3) articles decided by the whole church in a synod or symbol; (4) articles held by all orthodox divines as necessary. Not necessary, are dogmas (1) not contained in the Bible; (2) not belonging to the common inheritance of faith; (3) not unanimously taught by theologians; (4) left doubtful by grave divines; (5) not tending to piety, charity, and edification. He concludes with a defense of John Arnd (1555-1621), the famous author of "True Christianity," against the attacks of orthodox fanatics, and with a fervent and touching prayer to Christ to come to the rescue of his troubled church (Rev. 22: 17).

The golden sentence occurs in the later half of the tract (p. 128 in Luecke's edition), incidentally and in hypothetical form, as follows:-

"Verbo dicam: Si nos servaremus IN necesariis Unitatem, IN non-necessariis Libertatem, IN UTRISQUE Charitatem, optimo certe loco essent res nostrae." [In a word, I'll say it: if we preserve unity in essentials, liberty in non-essentials, and charity in both, our affairs will be in the best position.]

The same sentiment, but in a shorter sententious and hortative form, occurs in a book of Gregor Frank, entitled Consideratio theologica de gravibus necessitatibus dogmatum Christianorum quibus fidei, spei et charitatis officia reguntur [Theological discussion on the most serious essentials in Christian doctrine governing the duties of faith, hope and charity], Francf. ad Oderam, 1628. Frank (1585-1661) was first a Lutheran, then a Reformed theologian, and professor at Francfort. He distinguishes three kinds of dogmas: (1) dogmas necessary for salvation: the clearly revealed truths of the Bible; (2) dogmas which are derived by clear and necessary inference from the Scriptures and held by common consent of orthodox Christendom; (3) the specific and controverted dogmas of the several confessions. He concludes the discussion with this exhortation:-

"Summa est.: Servemus IN necessariis unitatem, IN non-necessariis libertatem, IN utrisque charitatem."

He adds, "Vincat veritas, vivat charitas, maneat libertas per Jesum Christum qui est veritas ipsa, charitas ipsa, libertas ipsa." [Let truth prevail, let charity prevail, let liberty abide through Jesus Christ who is truth itself, charity itself, freedom itself.]

Bertheau deems it uncertain whether Meldenius or Frank was the author. But the question is decided by the express testimony of Conrad Berg, who was a colleague of Frank in the same university between 1627 and 1628, and ascribes the sentence to Meldenius.

Fifty years dater Richard Baxter, the Puritan pacificator In England, refers to the sentence, Nov. 15, 1679, In the preface to The True and Only Way of Concord of All the Christian Churches, London, 1680, In a slightly different form: "I once more repeat to you the pacificator's old despised words, 'Si in necessariis sit [esset] unitas, in non necessariis libertas, in charitas, optimo certo loco essent rcs nostrae." Luecke was the first to quote this passage, but overlooked a direct reference of Baxter to Meldenius in the same tract on p. 25. This Dr. Briggs discovered, and quotes as follows:-

"Were there no more said of all this subject, but that of Rupertus Meldenius, cited by Conradus Bergius, it might end all schism if well understood and used, viz." Then follows the sentence. Baxter also refers to Meldenius on the preceding page. This strengthens the conclusion that Meldenius was the "pacificator." For we are referred here to the testimony of a contemporary of Meldenius. Samuel Werenfels, a distinguished irenical divine of Basel, likewise mentions Meldenius and Conrad Bergius together as ironical divines, and testes veritatis, and quotes several passages from the Paraenesis votiva.

Conrad Bergius (Berg), from whom Baxter derived his knowledge of the sentence, was professor in the university of Frankfurt-an-der-Oder, and then a preacher at Bremen. He and his brother John Berg (1587-1658), court chaplain of Brandenburg, were irenical divines of tile German Reformed Church, anti moderate Calvinists. John Berg attended the Leipzig Colloquy of March, 1631, where Lutheran and Reformed divines agreed on the basis of the revised Confession of 1540 in every article of doctrine, except the corporal presence and oral manducation. The colloquy "as ill advance of the spirit of the age, and had no permanent effect See Schaff, Creeds of Christendom I. 558 sqq., and Niemeyer, Collectio Confessionum in Eclesiis Reformatis publicatarum, p. LXXV. and 653-668

Dr. Briggs has investigated tile writings of Conrad Bergius and his associates in the royal library of Berlin. In his "Praxis Catholica divini canonis contra quasuis haereses et schismata," [Catholic practice of the divine canon against whatever heresies and schisms] etc., which appeared at Bremen in 1639, Bergius concludes with the classical word of "Rupertus Meldenius Theologus," and a brief comment on it. is quoted by Baxter in the form just given. In the autumn of 1627 Bergius preached two discourses at Frankfurt on the subject of Christian union, which accord d with the sentence, and appeared in 1628 with tile consent of the theological fatuity. They were afterwards incorporated in his Praxis Catholica. He was thoroughly at home in the polemics anti irenics of his age, anti can be relied on as to tile authorship of the sentence.

But who was Meldenius? This is still an unsolved question. Possibly he took his name from Melden, a little village on the borders of and Silesia. His voice was drowned, and his name forgotten, for two centuries, but is now again heard with increased force. I subscribe to the concluding words of my esteemed colleague, Dr. Briggs: "Like a mountain stream that disappears at times under tile rocks of its bed, and re-appears deeper down in the valley, so these long-buried principles of peace have reappeared after two centuries of oblivion, and these irenical theologians w ill be honored by those who live in a better age of the world, when Protestant irenics have well-nigh displaced tile old Protestant polemics end scholastics."

The origin of the sentence was first discussed by a Dutch divine, Dr. Van der Hoeven of Amsterdam, in 1847; then by Dr. Luecke of Goettingen Ueber das Alter, den Verfasser, die urspruengliche Form und den wahren Sinn des kirchlichen Friedenspruchs 'In necessariis unites,' etc., Goettingen 1850 (XXII. and 146 pages); with supplementary remarks in the "Studien und Kritiken " for 1851, p. 905-938. Luecke first proved the authorship of Meldenius. The next steps were taken by Dr. Klose, in the first edition of Herzog's "Theol. Encycl." sub vol. IX. (1858), p. 304 sq., and by Dr. Carl Bertheau, in the second edition of Herzog, IX. (1881), p. 528-530. Dr. Briggs has furnished additional information in two articles in the "Presbyterian Review," vol. VIII., New York, 1887, pp. 496-499, and 743-746.

From Steve Perisho, http://liberlocorumcommunium.blogspot.com/2010/03/in-necessariis-unitas-in-non.html (an interesting blog indeed), forwarded to me by Perisho. I quote/copy here in order to be sure of preserving the information, but the blog posting link may lead to comments and will assuredly lead to other interesting material on his site.

The earliest known occurrence of this so far is to my knowledge once again "Catholic", if somewhat dubiously so, given that the Dictionnaire de théologie catholique calls the De republica ecclesiastica "a very interesting blend of theses Anglican and Gallican" (vol. 4, col. 1670), and the 2nd edition of the New Catholic encyclopedia, De Dominis himself an "apostate":

In preparing vol. XVII of the Briefwisseling van Hugo Grotius I came across a letter which the French scholar Jean de Cordes addressed to Grotius on 9 November 1634 (Bodleian Library, Oxford, MS. D'Orville 51). In this letter the source of the adage is mentioned, be it rather vaguely: the works of Marc' Antonio de Dominis (1560-1624), archbishop of Split (Spalato). After some research I have found the device in book 4, chapter 8 of De republica ecclesiastica libri X, London/Hannover 1617-1622) i.e. “on p. 676 of the first volume published in London in 1617, at the end of chapter 8 of book 4, which treats of the papacy” (H. J. M. Nellen, "De zinspreuk 'In necessariis unitas, in non necessariis libertas, in utrisque caritas,'" Nederlands archief voor kerkgeschidenis 79, no. 1 (1999): 106, 104 (99-106)). Cf. http://spu.worldcat.org/title/marci-antonii-de-dominis-de-republica-ecclesiastica-libri-x/oclc/476586221. There (and on p. 104 of this article) it appears as follows:

Quod si in ipsa radice, hoc est sede, vel potius solio Romani pontificis haec abominationis lues purgaretur et ex communi ecclesiae consilio consensuque auferretur hic metus, depressa scilicet hac petra scandali ac ad normae canonicae iustitiam complanata, haberemus ecclesiae atrium aequabile levigatum ac pulcherrimis sanctuarii gemmis splendidissimum. Omnesque mutuam amplecteremur unitatem in necessariis, in non necessariis libertatem, in omnibus caritatem. Ita sentio, ita opto, ita plane spero, in eo qui est spes nostra et non confundemur.

Now if this plague of an abomination [were to] be cleared away at the root—i.e. see or rather throne of the Roman pontiff—itself, and [if] that fear hanging over the common counsel and consent of the Church (suppressed, of course, by this stone that makes men stumble [(cf. 1 Pet 2:8 in the Vulgate)], and reduced to the ‘equity’ of canon law) [were to] be removed, we would have an equitable atrium of the Church polished and [rendered] surpassingly brilliant by the beautiful gems of the sanctuary. And we would all embrace a mutual unity in things necessary; in things non necessary liberty; in all things charity. This I feel, this I desire, this I do indeed hope for, in him who is our hope and we are not confounded.

I would welcome any suggestions for the refinement of this translation.

This was quoted by De Cordes (who claimed to "ay trouvé [it] dans les oeuvres de Dominis") in his letter to Grotius dated 9 November 1634 (above) as follows:

in necessariis unitas, in non necessariis libertas et in omnibus charitas

(Nellen, 102). Grotius knew De Dominis personally, and, indeed, was in possession of this first volume of the De republica ecclesiastica by 1619 (Nellen, 103). But he wouldn't have been able to track the maxim down on the strength of this vague reference alone (Nellen, 104).

For additional passages in De Dominis' De republica ecclesiastica that give voice to similar sentiments, see Nellen, 104n20: bk. 7, chap. 6, sec. 21 (p. 104); bk. 7, chap. 9, sec. 18 (p. 130); bk. 7, chap. 9, sec. 27 (p. 132); bk. 7, chap. 9, sec. 204 (p. 197); bk. 7, chap. 12, sec. 113 (p. 316).

Would the presence of De Dominis in England go some way towards accounting for the major role played by Richard Baxter (1615-1691) in the dissemination of the maxim several decades later? "The apostacy [(geloofsafval)] of the Archbishop and his flirtation with Anglicanism made him for representatives of the Reformation an important trump card in the religious controversy with Rome" (Nellen, 105)—for as long, at least, as that flirtation lasted. And quite probably longer.

Prior to this ground-breaking article by Nellen (which, he admits, may well be superceded by "the definitive answer" published "in 2065—or perhaps much earlier" (Nellen, 101)), the consensus of more than a century had been that it was the work of Peter Meiderlin (1582-1651) (anagrammatico-pseudonymously Rupertus Meldenius), and appeared for the very first time in the first (i.e. 1626) printing of his Paraenesis votiva pro pace ecclesiae ad theologos Augustanae Confessionis (http://spu.worldcat.org/title/paraenesis-votiva-pro-pace-ecclesiae-ad-theologos-augustanae-confessionis/oclc/34765422):

Verbo dicam: si nos servaremus in necessariis unitatem, in non necessariis libertatem, in utrisque caritatem, optimo certe loco essent res nostrae.

(Meiderlin's Paraenesis was so rare that Friedrich Lücke reproduced it in an appendix to his Über das Alter, den Verfasser, die ursprüngliche Form und den wahren Sinn des kirchlichen Friedenssprüches "In necessariis unitas, in non necessariis libertas, in utrisque caritas": eine literar-historische theologische Studie (Göttingen: Dieterich, 1850).)

"Meiderlin is [therefore] a disciple of Johann Arndt, but he seeks less to defend the ideas of his master (in whom one can see a precursor of 'Pietism') than to bring an end to the dogmatic rivalries of the theologians of the Augsburg Confession" (Joseph Lecler, "À propos d'une maxime citée par le Pape Jean XXIII: In necessariis unitas, in dubiis libertas, in omnibus caritas," Recherches de science religieuse 49 (1961): 552 (549-560)).

In Catholic (but also some Protestant) hands, dubiis was substituted for non necessaries [(note also the presence of omnibus rather than, as in Meiderlin, utrisque)], and this had supposedly the effect of extending "the rule of Meldenius . . . to much more than just the necessaria [(for salvation)] and the non necessaria [(for salvation)]", much more than just the "fundamental articles": "the tripartite maxim. . . . [thus] lost its original Protestant nuance, in order to extend liberty to the entire domain of questions debated, doubtful, and undefined [(non définies par l'Église)]" (Lecler, 559-560). There are many helpful references to the literature (but most notably Krüger and Eekhof) in Lecler, who isn't doing much in the way of original scholarship, but mostly summarizing the work of others (Eekhof and Krüger, and, for more than a century total behind them, Bauer, Lücke, and Morin).

But the 1999 article by Nellen has, for now at least, returned this once again to (a dubious) "Catholicism".

Here is a bit more in the way of 20th- and 21-century bibliography, thrown in quite willy nilly as encountered. I do not claim to have read what follows, nor that this list is anything even close to exhaustive.

Burr, Viktor. "Zur Geschichte des Wahlspruches: In necessariis unitas, in dubiis libertas, in omnibus caritas." In 110 Jahre Unitas-Salia zu Bonn/1847 bis 1957 - Festschrift zum 110. Stiftungsfest des W.K.St.V. Unitas-Salia, der Mutterkorporation des Unitas-Verbandes, edited by Anton Brenig, 7-24. Bonn, 1957.

Posted by Steve Perisho at 8:12 PM