The recent promulgation of the motu proprio Traditionis Custodes by the Most Holy Lord Francis has sparked renewed interest in the question of the limits of papal power, especially as it relates to liturgical tradition.
Any such discussions must take into account the Indiculum Pontificis (“The Pontiff’s Attestation”), an oath that popes seem to have sworn between the 7th and 11th centuries. In it, the pontiff-elect solemnly vows to St. Peter that he shall preserve inviolate the doctrinal and liturgical tradition handed down to him by his predecessors and by the holy œcumenical councils and that he will act as a remora against the introduction of any novelties.
This papal oath is preserved in the Liber Diurnus Pontificum Romanum, a collection of formulæ used by the pontifical chancellery which survives today in three MSS.: Vatican City, Archivio Segreto Vaticano, Misc. Arm. XI.19; Milan, Biblioteca Ambrosiana I.2 sup.; and the Codex Claramontanus now kept in the Abbey of Egmond-Binnen. A modern edition was published by the Jesuit Jean Garnier in 1680, reprinted in the Patrologia Latina (vol. 105, cols. 21-118). In 1869, Marie Louis Thomas Eugène de Rozière published an improved edition, followed by Theodor E. von Sickel’s critical edition in 1889. Finally, in 1958 Hans Foerster published diplomatic editions of all three MSS. The Indiculum Pontificis appears as formula 83 in the Vatican MS., 59 in the Ambrosian, and 64 in the Codex Claramontanus.
Sickel concluded that the texts of the Liber Diurnus developed over time and that the MSS. that survive to-day represent its state during the reign of the Most Holy Lord Hadrian I, between the end of the 8th and the beginning of the 9th centuries. Some have argued, withal, that some of its formulæ date back as early as the pontificate of St. Gregory the Great. Gottfried Buschbell argued in 1896 that it stopped being used after 787, in his 1948 book on the Photian schism Francis Dvornik makes an excellent case for its continued use in the 11th century, when Cardinal Deusdedit wrote a compilation of canon law and included the papal oath therein. It is tempting to connect its fall into desuetude with the expansive views of papal power adopted by St. Gregory VII and his reformist successors.
What is known is that in 1352 the cardinals forced the Lord Innocent VI to swear an oath, but it is entirely different from the one in the Liber Diurnus and only concerned with tithes and administrative procedures. Sometime in the 14th century, an oath based on the one in the Liber Diurnus was forged with the addition of a statement precluding the possibility of papal abdication, and it was used by the Lord Boniface VIII’s enemies to argue that his predecessor’s abdication had been null and void.
In the early 15th century, another papal oath was forged, again based on the authentic oath from the Liber Diurnus, and falsely presented as the text sworn by the Lord Boniface VIII at his coronation. The reformist party in the Council of Constance used this forged oath to compose a new oath for popes to swear during their coronation (session 39), but this legislation does not seem to have received papal approval.
We reproduce below the text of the Indiculum from the Vatican MS. as it appears in Foerster’s edition, together with the first full English translation thereof.
The Pontiff’s Attestation [of Faith]
In the name of our Lord God and Saviour Jesus Christ, and so forth, on (such) indiction, (such) month, (such) day.
I, (name), by the mercy of God deacon, elect and future bishop, by the grace of God, of this Apostolic See, swear to you, blessed Peter, prince of the Apostles—to whom the Lord Jesus Christ, Creator and Redeemer of all, gave the keys of the kingdom of heaven to bind and loose in heaven and on earth saying, “Whatsoever thou shalt bind upon earth, shall be bound also in heaven, and whatsoever thou shalt loose upon earth, shall be loosed also in heaven”—and to your Holy Church, which today I have taken up to rule under your protection, that I shall guard with all my strength, even unto giving up the ghost or shedding my blood, the right and true faith which, having been handed down by Christ its author and transmitted by your successors and disciples unto my smallness, I found in your Holy Church; and with your help I shall patiently bear the difficulties of the times; I shall preserve the the mystery of the holy and individual Trinity which is one God, as well as the dispensation according to the flesh of the only-begotten Son of God, Our Lord Jesus Christ, and the other dogmas of God’s Church, just as they are deposited by the universal councils and constitutions of the apostolic pontiffs and the writings of the most approved doctors of the Church, that is, all that concerns the rightness of your and our orthodox faith handed down by you; I, too, shall guard unaltered even by a tittle the holy and universal councils—of Nicæa, of Constantinople, the first of Ephesus, of Chalcedon, and the second of Constantinople which was celebrated in the time of the prince Justinian of happy memory—and together with them I shall fully and entirely keep with equal honour and veneration the holy sixth council which recently assembled under prince Constantine of happy memory and the apostolic lord Agatho my predecessor, and I shall preach whatsoever they preached and condemn in heart and word whatsoever they condemned; I shall moreover diligently and heartily confirm and safeguard undiminished all the decrees of the apostolic pontiffs my predecessors, and whatever they promulgated and confirmed in synod and individually, and maintain them in unwavering vigor just as my predecessors established them, and condemn with a sentence of equal authority whatever things and persons they condemned and rejected; I shall keep inviolate the discipline and ritual of the Church just as I found and received it handed down by my predecessors, and I shall preserve the Church’s property undiminished and take care it is kept undiminished; I shall neither subtract nor change anything from the tradition my most esteemed predecessors have safeguarded and I have received, nor shall I admit any novelty, but shall fervently keep and venerate with all my strength all that I find handed down as, forsooth, my predecessors’ disciple and follower; but if anything should come about contrary to canonical discipline, I shall correct it, and guard the sacred canons and constitutions of our pontiffs as divine and heavenly mandates, knowing that at the divine Judgment I shall render a strict account of all that I profess to you whose place I occupy by divine condescension and whose role I fulfill by the aid of your intercession. If I should presume or allow anyone else to presume to do anything that exceeds these, then on that terrible day of God’s judgment be propitius to me in my sincere attempt to guard them and lend your aid, I pray, to me who am set in this corruptible life, that I might appear blameless before the sight of our Lord Jesus Christ, the Judge of all, when he shall come fearfully to judge our sins, that he might make me to stand on the Father’s right hand among his faithful disciples and successors. I have signed this my profession with my own hand, as contained above—put into writing by (name), notary and secretary, at my command—and with a pure mind and devout conscience I have sincerely offered it to you, blessed Peter, apostle and prince of all the apostles, by this bodily oath.
I, the aforestated (name), unworthy deacon and by the grace of God bishop-elect of this apostolic see of the Roman Church, made this my profession, as contained above, presented this bodily oath, and offered it to you, blessed Peter, prince of the apostles, with a pure mind and conscience.
In nomine Domini Dei Saluatoris nostri Iesu Christi et cetera, indictione ill. mense ill. die ill.
Ill. misericordia Dei diaconus et electus futurusque per Dei gratiam huius apostolicae sedis antistis tibi profiteor, beate Petre apostolorum princeps, cui claues regni caelorum ad ligandum atque soluendum in caelo et in terra creator atque redemptor omnium Dominus Iesus Christus tradidit, inquiens: «Quaecumque ligaueris super terram, erunt ligata et in caelo, et quaecumque solueris super terram, erunt soluta et in caelis», sanctaeque tue Ecclesiae quam hodie tuo praesidio regendam suscepi, quod uere fidei rectitudine, Christo auctore tradente, per successores tuos atque discipulos usque ad exiguitatem meam perlatam in tua sancta Ecclesia repperi, totis conatibus meis usque ad animam et sanguinem custodire; temporumque difficultate cum tuo adiutorio tolleranter sufferre; tam de sanctae et indiuidue Trinitatis misterio quae unus est Deus, quamque de dispensatione quae secundum carnem facta est unigeniti Filii Dei Domini nostri Iesu Christi et de ceteris Ecclesiae Dei dogmatibus, sicut uniuersalibus conciliis et constitutis apostolicorum pontificum probatissimorumque doctorum Ecclesiae scriptis sunt commendata, id est queque ad rectitudinem uestrae nostraeque orthodoxe fidei a te traditionem respiciunt, conseruare; sancta quoque uniuersalia concilia: Nicenum, Constantinopolitanum, Efesenum primum, Calcedonensem et secundum Constantinopolitanum quod Iustiniani piae memoriae principis temporibus celebratum est, usque ad unum apicem inmutilata seruare, et unam cum eis pari honore et ueneratione sanctum sextum concilium quod nuper sub Constantino piae memoriae principe et Agathone apostolico praecessore meo conuenit, medullitus et plenius conseruare, quaeque uero praedicauerunt, praedicare, queque condemnauerunt, ore et corde condemnare; diligentius autem et uiuacius omnia decreta predecessorum apostolicorum nostrorum pontificum, queque uel synodaliter uel specialiter statuerunt et probata sunt, confirmare et indiminute seruare, et sicut ab eis statuta sunt, in sua uigoris stabilitate custodire, quaeque uel quosque condemnauerunt uel abdicauerunt, simili auctoritatis sententia condemnare; disciplinam et ritum Ecclesiae, sicut inueni et a sanctis predecessoribus meis traditum repperi, inlibatum custodire, et indiminutas res Ecclesiae conseruare et ut indiminute custodiantur operam dare; nihil de traditione quae a probatissimis praedecessoribus meis seruatum repperi, diminuere uel mutare aut aliquam nouitatem admittere, sed feruenter, ut uere eorum discipulus et sequipeda, totis meae conatibus quae tradita comperio, conseruare ac uenerare; si qua uero emerserint contra disciplinam canonicam, emendare, sacrosque canones et constituta pontificum nostrorum ut diuina et celestia mandata custodire, utpote tibi redditurum me sciens de omnibus quae profiteor districtam in diuino iudicio rationem, cuius locum diuina dignatione perago et uicem intercessionibus tuis adiutus impleo. Si preter haec aliquod agere presumpsero uel ut presumatur permisero, eris autem mihi in illa terribili die diuina iudicii Dei, propitius haec conanti et diligenter seruare curanti adiutorium quoque ut prebeas obsecro in hac uita corruptibili constituto, ut inreprehensibilis appaream ante conspectum iudicis omnium Domini nostri Iesu Christi, dum tertibiliter de commissis aduenerit iudicare, ut faciat me dextre partis compotem et inter fideles discipulos ac successores esse consortem. Quam professionem meam, ut supra continet, per ill. notarium et scriniarium me mandante conscriptam propria manu subscripsi et tibi, beate Petre apostole et apostolorum omnium princeps, pura mente et conscientia deuota corporali iureiurando sinceriter optuli.
Ego qui supra ill. indignus diaconus et Dei gratia electus huius apostolicae sedis Romane Ecclesiae hanc professionem meam, sicut supra continet, faciens et iusiurandum corporaliter offerens tibi, beate Petre apostolorum princeps, pura mente et conscientia optuli.
 Cf. John Monaco, “Was the Sacred Liturgy made for the pope, or the pope for the Sacred Liturgy?”, Catholic World Report; Martin Mosebach, “Mass and Memory,” First Things; Peter Kwasnewski, “The Pope’s Boundedness to Tradition as Legislative Limit: Replying to Ultramontanist Apologetics” (upcoming)
 The reading of the MS is here corrupt. Sickel suggests traditae for traditionem.
 Sickel suggests adding mentis.