His Holiness St. Pius X issued the Anti-Modernist oath on September 1, 1910, and intended that "all clergy, pastors, confessors, preachers, religious superiors, and professors in philosophical-theological seminaries" should subscribe to it. The oath continued in use until the mid 1960s.

Pius X instituted the oath to stop modernist ideas, and to explicitly clarify Catholic teaching to those who taught it. This requirement arose because Modernism, though it did not heretically tend towards schism, nevertheless caused people to believe they were true Catholics while having a different idea of what that meant.

The full text of the Anti-Modernist oath appears here. The discussion below analyses its key points.

"I N. firmly embrace and accept each and every definition that has been set forth and declared by the unerring teaching authority of the Church, especially those principal truths which are directly opposed to the errors of this day."

Even in the wording of this first line one can see a contradiction of the Modernist Catholic standpoint. The use of the word "definition" is very important in the Catholic Church's view of what it teaches. Namely, all that it teaches it has really always taught, but it is called to define more precisely due to changing circumstances. One of the main tenets of Modernism is that what the Church believes changes over time and one of the mechanisms for this are those definitions.

"And first of all, I profess that God, the origin and end of all things, can be known with certainty by the natural light of reason from the created world (cf. Rom. 1:90), that is, from the visible works of creation, as a cause from its effects, and that, therefore, his existence can also be demonstrated:"

This means that that the Catholic teaching is that anyone, even without being told by other people about God, or by hearing it from the Catholic Church, can figure out that God really does exist based on observation and reasoning. While the Catholic Church believes some things can not be known about him without him telling us that, it does not believe God is completely uknowable in any way by our human mind. Basically in the same way that we can use our mind and observation to figure out the world is round, the Catholic Church believes that the existence of God can be known in that same manner. This and the next statements in the anti modernist oath are to counter the general idea God can't be really known for sure, and that faith is a feeling.

"Secondly, I accept and acknowledge the external proofs of revelation, that is, divine acts and especially miracles and prophecies as the surest signs of the divine origin of the Christian religion and I hold that these same proofs are well adapted to the understanding of all eras and all men, even of this time."

It is not the Catholic Church's position that they learned about God and the ultimate fate of man by a sort of intuition, feeling, or fantasy; but that a man called Jesus said he was God, and proved it by doing miracles (which are things only God could do). This concept of divine revelation proved by miracles is the crux of the reasoning of the Catholic Church. According to the Church, the Apostles did not follow Jesus simply because he seemed nice, but because did things in front of their very eyes which proved he was God. These Apostles then spread that news and his teaching, and this is what the Catholic Church is.

"Thirdly, I believe with equally firm faith that the Church, the guardian and teacher of the revealed word, was personally instituted by the real and historical Christ when he lived among us, and that the Church was built upon Peter, the prince of the apostolic hierarchy, and his successors for the duration of time."

A note on the use of the world "real" in this line. One can deny that Jesus did not really exist and was not "real" and "historical", and therefore not follow the Catholic religion. But the Catholic Modernist would agree that Jesus was not "real" and "historical" but still follow the Catholic Religion anyway, saying that it was good for it to exist because it made people happy, fed the poor, etc. It is to contradict this mentality that the word "real" was used here.

"Fourthly, I sincerely hold that the doctrine of faith was handed down to us from the apostles through the orthodox Fathers in exactly the same meaning and always in the same purport. Therefore, I entirely reject the heretical' misrepresentation that dogmas evolve and change from one meaning to another different from the one which the Church held previously."

This idea of the evolution of dogmas is central to the Modernist thinking. This allows them to believe something different and not be contradicted by older writings, documents, etc. that state the contrary. This makes them unique in the history of heresies: previously heretics would either state that they had maintained the true teaching from time immemorial, or that the present teachers had turned wrong. Modernism allowed for the past teachers to be right and the Modernists to be right as well, because "right" itself changes.

"Furthermore, with due reverence, I submit and adhere with my whole heart to the condemnations, declarations, and all the prescripts contained in the encyclical Pascendi and in the decree Lamentabili, especially those concerning what is known as the history of dogmas."

This is the same point made again, to be as explicit as possible.

"Likewise, I reject that method of judging and interpreting Sacred Scripture which, departing from the tradition of the Church, the analogy of faith, and the norms of the Apostolic See, embraces the misrepresentations of the rationalists and with no prudence or restraint adopts textual criticism as the one and supreme norm."

This passage makes reference to textual criticism of the Bible. The idea of trying to understand the Bible by reading it without any regard to any external information known or that can be known about it.

"The purpose of this is, then, not that dogma may be tailored according to what seems better and more suited to the culture of each age;"

Central to the Modernist idea of the evolution of dogmas was that the dogmas be tailored to the current times. For example, if everyone presently wants women to be priests, then the dogma concerning the priesthood should change.

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