First Vatican Council
1869 to 1870 A.D. under Pope Blessed Pius IX
The 20th of 21 Ecumenical Councils
POSTULATUM OF THE BISHOPS
FOR THE DEFINITION OF INFALLIBILITY:
To The Holy Ecumenical Vatican Council
The undersigned Fathers humbly and earnestly beg the holy Ecumenical Council of the Vatican to define clearly, and in words that cannot be mistaken, that the authority of the Roman Pontiff is supreme, and, therefore, exempt from error, when in matters of faith and morals he declares and defines what is to be believed and held, and what is to be rejected and condemned, by all the faithful.
Reasons For Which The Definition Is Thought Opportune And Necessary
The Sacred Scriptures plainly teach the Primacy of jurisdiction of the Roman Pontiff, the Successor of St. Peter, over the whole Church of Christ, and, therefore, also his Primacy of supreme teaching authority.
The universal and constant tradition of the Church, as seen both in facts and in the teaching of the Fathers, as well as in the manner of acting and speaking adopted by many Councils, some of which were Ecumenical, teaches us that the judgments of the Roman Pontiff in matters of faith and morals are irreformable.
In the Second Council of Lyons, with the consent of both Greeks and Latins, a profession of faith was agreed upon, which declares: "When controversies in matters of faith arise, they must be settled by the decision of the Roman Pontiff." Moreover, in the Ecumenical Synod of Florence, it was defined that "the Roman Pontiff is Christ's true Vicar, the Head of the whole Church, and Father and Teacher of all Christians; and that to him, in blessed Peter, was given by Jesus Christ the plenitude of power to rule and govern the universal Church." Sound reason, too, teaches us that no one can remain in communion of faith with the Catholic Church who is not of one mind with its head, since the Church cannot be separated from its head, even in thought.
Yet some have been found, and are even now to be found, who, boasting of the name of Catholic, and using that name to the ruin of those weak in faith, are bold enough to teach, that sufficient submission is yielded to the authority of the Roman Pontiff, if we receive his decrees in matters of faith and morals with an obsequious silence, as it is termed, without yielding internal assent, or, at most, with a provisional assent, until the approval or disapproval of the Church has been made known. Anyone can see that by this perverse doctrine the authority of the Roman Pontiff is overturned, all unity of faith dissolved, a wide field open to errors, and leisure afforded for spreading them far and wide.
Therefore, the Bishops, the guardians and protectors of Catholic truth, have endeavored, especially nowadays, to defend in their Synodal decrees, and by their united testimony, the supreme authority of the Apostolic See. 
But the more clearly Catholic truth has been declared, the more vehemently has it been attacked both in books and in newspapers, for the purpose of exciting Catholics against sound doctrine, and preventing the Council of the Vatican from defining it.
And even if, in times past, many may have doubted the opportuneness of declaring this doctrine in the present Ecumenical Council, it would seem now to be absolutely necessary to define it. For Catholic doctrine is now once more assailed by those same arguments which men, condemned by their own conscience, used against it in past times -- arguments which, if carried to their ultimate consequences, would bring to the ground the very Primacy of the Roman Pontiff and the infallibility of the Church herself; and to which, also, is frequently added the most violent abuse of the Apostolic See. Nay, more; the most bitter assailants of Catholic doctrine, though calling themselves Catholics, are not ashamed to assert that the Synod of Florence, which so clearly declares the supreme authority of the Roman Pontiff, was not Ecumenical.
If then, the Council of the Vatican, being thus challenged, were to be silent, and omit to give testimony to Catholic doctrine on this point, then Catholics would, in fact, begin to doubt the true doctrine, and the novelty-mongers [Lat. neoterici, from Gr. neotericoi, lit. "new poets"] would triumphantly assert that the Council had been silenced by the arguments brought forward by them. They would, moreover, abuse this silence on every occasion, and openly deny the obedience due to the judgments and decrees of the Apostolic See in matters of faith and morals, under pretext that the judgment of the Roman Pontiff is fallible on such points.
Therefore the public good of Christianity seems to require that the holy Council of the Vatican, professing once again, and explaining more fully, the Florentine decree, should define clearly, and in words that can admit of no doubt, that the authority of the Roman Pontiff is supreme, and, therefore, exempt from error, when in matters of faith and morals he decrees and ordains what is to be believed and held by all the faithful of Christ, and what is to be rejected and condemned by them.
There are, indeed, some who think that this Catholic truth should not be defined, lest schismatics and heretics should be repelled yet further from the Church. But, above all other considerations, Catholics have a right to be taught by the Ecumenical Council what they are to believe in so weighty a matter, and one which has been of late so iniquitously attacked; lest this pernicious error should in the end infect simple minds, and the masses of people unawares. Hence it was that the Fathers of Lyons and of Trent deemed themselves bound to establish the doctrine of the truth, notwithstanding the offence that might be taken by schismatics and heretics.
For if these seek the truth in sincerity, they will not be repelled, but, on the contrary, drawn towards us, when they see on what foundations the unity and strength of the Catholic Church chiefly repose. But, should any leave the Church in consequence of the
true doctrine being defined by the Ecumenical Council, these will be few in number, and such as have already suffered shipwreck in the faith; such as are only seeking a pretext to abandon that Church by an overt act, which they plainly show they have deserted already in heart. These are they who have never shrunk from disturbing our Catholic people; and from the snares of such men the Council of the Vatican ought to protect the faithful children of the Church. For all true Catholics, taught and accustomed to render the fullest obedience both of thought and word to the Apostolic decrees of the Roman Pontiff, will receive with joyful and devoted hearts the definition of the Council of the Vatican concerning his supreme and infallible authority.
 Many specimens of this testimony are collected in the following Appendix to the Postulatum.
APPENDIX TO THE POSTULATUM
Decisions Of Provisional Synods Recently Held, Showing The Common Opinion Of Bishops Concerning The Supreme And
Infallible Authority Of The Roman Pontiff In Matters Of Faith And Morals.
1. The Provincial Council held at Cologne in 1860, to which, in addition to his Eminence Cardinal Geissel, Archbishop of Cologne, five Bishops subscribed, expressly declared: "He (the Roman Pontiff) is the father and teacher of all Christians, whose judgment in questions of faith is 'per se' unalterable."
2. The Bishops assembled in the Provincial Council, held at Utrecht in 1865, most openly assert: "We unhesitatingly hold that the judgment of the Roman Pontiff in matters which refer to faith and morals is infallible."
3. The Provincial Council of Prague,  in 1860, to which his Eminence Cardinal Archbishop Frederic de Schwarzenberg and four other Bishops subscribed, under the heading, "On the Primacy of the Roman Pontiff," decreed as follows : "We reject, moreover, the error of those who pretend that the Church can exist anywhere without being joined in bonds of union with the Church of Rome, in which the tradition which has been handed down by the Apostles, has been preserved by those who are in every part." (S. Irenaeus, Adv. Hoer. 1. 3, c. 3, n. 2.)
"We know that no one who is not joined to the Head can be considered as a member of the Body of the Church which Christ founded on Peter, and established on his authority. Let all then prefer to confess with us and with the multitude of orthodox believers spread over the whole world, the Headship of the Roman Church and the Primacy of the Roman Pontiff; let them, as is fitting, with us, reverence and honor with dutiful affection our Most Holy Father Pius IX, by God's Providence Pope, the lawful Successor of the Prince of the Apostles, the Vicar of Christ on earth, the Chief Teacher of Faith, and Pilot of the Ship of Christ, to whom the most exact obedience and internal assent is due from all who wish to belong to the fold of Christ.
We declare and teach, that this authority of the Roman Pontiff comes from Christ our Lord, and that consequently it is dependent upon no power or favor of men, and remains unimpaired in all times, even in the most bitter persecutions which the Church of Rome has suffered, as was the case during the imprisonment and martyrdom of blessed Peter."
4. The Provincial Council of Kalocza, held in 1860, declared: "That as Peter was ... the irrefutable teacher of the doctrines of faith, for whom the Lord Himself prayed that his faith might not fail; so his legitimate successors seated aloft on the Chair of Rome ... preserve the deposit of faith with Supreme and irrefutable powers of declaring the truth.... Therefore we also reject, proscribe, and forbid all the faithful of this Province, to read or maintain, and much more to teach, the propositions published by the Gallican Clergy in 1682, which have already been censured this same year by the Archbishop of Gran, of pious memory, and by the other Bishops of Hungary."
5. The Plenary Council of Baltimore, which met in 1866, and to which 44 Archbishops and Bishops subscribed, says: "The living and infallible authority flourishes in that Church alone which was built by Christ upon Peter, who is the Head, Leader, and Pastor of the whole Church, whose faith Christ promised should never fail -- which has always had legitimate Pontiffs, dating their origin in unbroken line from Peter himself, being seated in his Chair, and being the inheritors and defenders of the like doctrine, dignity, office, and power.
And because, where Peter is, there also is the Church, and because Peter speaks in the person of the Roman Pontiff and ever lives in his successors, passes judgment, and makes known the truths of faith to those who seek them, therefore the Divine declarations are to be received in that sense in which they have been and are held by this Roman See of blessed Peter, that mother and teacher of all Churches, which has always preserved whole and entire the teaching delivered by Christ, and which has taught it to the faithful, showing to all men the paths of salvation and the doctrine of everlasting truth."
6. The first Provincial Council of Westminster, held in 1852, states: "When our Blessed Lord exhorts us, saying, 'Look to the rock whence you are hewn ... look to Abraham your father' (Isaiah 51:1-2), it is fitting that we who have received our faith, our priesthood, and the true religion, directly from the Apostolic See, should more than others be attached to it by the bonds of love and fidelity.
Therefore do we maintain that foundation of truth and orthodoxy which Jesus Christ willed should be maintained unshaken; namely, the See of Peter, the teacher and mother of the whole world, the Holy Roman Church. Whatever is once defined by it, for that very reason alone, we consider to be fixed and certain; when we look at its traditions, rites, pious customs, discipline, and all its Apostolic Constitutions, we follow and cherish them with all the affection of our hearts. In fine, we of set purpose publicly declare our obedience and respect for the Pope as Christ's Vicar, and we remain united to him in the closest bonds of Catholic unity."
7. Nearly five hundred of the Bishops assembled in Rome to celebrate the Centenary of the Martyrdom of SS. Peter and Paul, in the year 1867, had no hesitation in addressing Pius IX in the following terms: "Believing that Peter has spoken by the mouth of Pius, whatever has been said, confirmed, and decreed by You to preserve the deposit of faith, we also repeat, confirm, and profess, and with one mind and heart we reject all that You have judged it necessary to reprove and condemn as contrary to Divine faith, to the salvation of souls, and to the good of society. For what the Fathers of Florence defined in their Decree of Union, is firmly and deeply impressed in our minds; that the Roman Pontiff is the Vicar of Christ, the Head of the whole Church, the Father and Teacher of all Christians."
 The Provincial Council of Prague (1860) was not included in the original draft from which the Latin is taken.
[Translation by Cardinal Henry Edward Manning, Roman Catholic Archbishop of Westminster, from his book 'The Vatican Council and Its Definitions', (New York: D. & J. Sadlier, 1871). This text is out of copyright and in the public domain; edited by Ronald L. Conte Jr.]