For those who rightly believe that the Catholic Faith is the true Faith, there are four levels of Catholic teaching that a person must assent to, each having a different level of authority.

1) Solemn Magisterium
2) Ordinary and Universal Magisterium
3) Ordinary Magisterium.
4) Teachings of Saints, Doctors, etc.

[First[/b], the Solemn or Extraordinary Magisterium is any infallibly defined (divinely revealed) dogma. Here are the criteria for infallibility, there are four of them.

Pope Pius IX, Vatican Council, 1870 Session 4, Chapter 4, Paragraph 9: "Therefore, faithfully adhering to the tradition received from the beginning of the Christian faith, to the glory of God our savior, for the exaltation of the Catholic religion and for the salvation of the Christian people, with the approval of the Sacred Council, we teach and define as a divinely revealed dogma that when the Roman Pontiff speaks EX CATHEDRA, that is, when, in the exercise of his office as shepherd and teacher of all Christians [number 3 below], in virtue of his supreme apostolic authority [number 2 below], he defines a doctrine concerning faith or morals to be held by the whole Church [number 1 below], he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith or morals. Therefore, such definitions of the Roman Pontiff are of themselves, and not by the consent of the Church, irreformable."

To paraphrase, what this means is that the pope cannot err when:

1) Teaching on faith and morals
2) In virtue of his apostolic authority
3) With the intent of binding all Christians to belief/obedience

There is one more thing that pertains to infallibility, from the same Council:

Pope Pius IX, Vatican Council, 1870 Session 4, Chapter 4, Paragraph 6: "For the Holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles."

4) Something that is already contained in the deposit of faith handed down by the Apostles and not a new doctrine.

Any Papal statement that meets the previous 4 points is infallible and God the Holy Ghost has spoken through the lips of the Pontiff. To willingly deny any such teaching severs one immediately from the Body of Christ; such a person is a heretic. Any Catholic who unwittingly believes a material heresy, that is accidentally and unknowingly believes contrary to such a teaching is generally understood to be still Catholic, unless their heretical understanding contradicts the divine or natural law or unless they reject the truth when they are presented with evidence of it (ie, the relevant Papal decree, etc...), or unless the heretical belief they hold is contrary to a necessary dogma of the Catholic Faith contained in the basic Christian Creed (such as the Trinity or the Incarnation). Such infallible teachings are Ecuмenical Councils approved by the Pope, any papal teaching with an anathema attached, some encyclicals or PORTIONS of encyclicals reaching the criteria of infallibility, and some Papal bulls. Also, the opposite statement of any proposition condemned by the pope as heretical, is also an infallible dogma.

This is where many people often get hung up. They proclaim with their lips that they believe in the dogmas, when in reality they deny them. Just how is a person to believe a dogma? Are we to wait for some theologian or priest to explain it to us? Not at all. We simply need to read these precious words of God the Holy Ghost, very, very carefully, and believe and obey their objective sense, as evidenced by the following teachings:

Pope Pius IX, Vatican Council, Session 3, Chapter 4, ex cathedra: "Hence, too, that meaning of the sacred dogmas is ever to be maintained which has once been declared by Holy mother Church, and there must never be any abandonment of this sense under the pretext or in the name of a more profound understanding."

As is clear, the meaning of a dogma is to be maintained as it has been declared, not as it has been explained by this or that saint or theologian. This is why wise Catholics read the ecuмenical Councils and other ex cathedra statements and believe them in all simplicity, exactly as they are written.

Second, adhere to all the teachings of the Ordinary and Universal Magisterium. The Ordinary and Universal Magisterium consists of teachings that have been held by unanimous consent of the Fathers of the Church, but have not been solemnly declared as above.

Pope Paul III, Council of Trent, Session 4, AD 1546: "Furthermore, in order to restrain petulant spirits, It decrees, that no one, relying on his own skill, shall,--in matters of faith, and of morals pertaining to the edification of Christian doctrine, --wresting the sacred Scripture to his own senses, presume to interpret the said sacred Scripture contrary to that sense which holy mother Church,--whose it is to judge of the true sense and interpretation of the holy Scriptures,--hath held and doth hold; or even contrary to the unanimous consent of the Fathers; even though such interpretations were never (intended) to be at any time published. Contraveners shall be made known by their Ordinaries, and be punished with the penalties by law established."

This means that if many of the fathers held different opinions on interpreting the Scriptures on such and such a doctrine, while other Fathers interpreted it otherwise, then we are not bound to believe either interpretation as divinely revealed. Only if the Church Fathers was unanimous when they taught concerning the point of revelation, can we say that their teachings on the matter are to be held as a divinely revealed dogma.

Teachings of the Ordinary and Universal Magisterium are to be believed by Divine and Catholic Faith, that is to say they are Divinely revealed, inerrant dogmas, as Pope Pius IX defined:

Pope Pius IX, Vatican Council, Session 3, Chapter 3: "Wherefore, by divine and Catholic faith all those things are to be believed which are contained in the word of God as found in Scripture and tradition, and which are proposed by the Church as matters to be believed as divinely revealed, whether by her solemn judgment or in her Ordinary and Universal Magisterium.[/b]"

Further proof that these interpretations are to be understood as dogmas of the Ordinary and Universal Magisterium comes from the Profession of Faith uttered by the same pope:

Pope Pius IX, Vatican Council, Session 2, #1, #3, ex cathedra: "I, Pius, bishop of the Catholic Church, with firm faith... accept Sacred Scripture according to that sense which Holy mother Church held and holds, since it is her right to judge of the true sense and interpretation of the Holy Scriptures; nor will I ever receive and interpret them except according to the unanimous consent of the Fathers."

If it is forbidden even to the pope, the one who is given the power, by God Himself, of defining the dogmas of faith, to interpret Scripture in a sense contrary to the unanimous consent of the Fathers, then it logically follows that such interpretations of the Scriptures are indeed dogmas of the Ordinary and Universal Magisterium.

This Magisterium, by the fact that is consists of divinely revealed dogmas, can and will never be contrary to the Extraordinary (Solemn) Magisterium, which consists of the same, and vice versa.

Pope Leo X, Apostolici Regiminis, 1513: "As truth cannot contradict truth, we declare every assertion contrary to the truth of Divine faith to be absolutely false, and strictly forbid any one to teach differently; we command that those who adhere to such assertions shall be avoided and punished, as men who seek to disseminate damnable heresies."

To willfully reject a teaching of the Ordinary and Universal Magisterium is the mortal sin of heresy.

Third, consent to the teachings of the Ordinary Magisterium, understanding that these teachings, while reliable, are not guaranteed by God the Holy Ghost to be free of error. The Ordinary Magisterium is any teaching issued by the pope while exercising his Ordinary teaching capacity, such as some encyclicals, sermons, addresses to different groups, etc... While these demand assent of intellect and will and our obedience, they are fallible, liable to error, and thus are subject to future correction. If a later ex cathedra (infallible) decree contradicts a previous pope's ordinary (fallible) teaching, we must assent to the ex cathedra decree.

Fourth, follow the examples and teachings of our great Church Fathers, Doctors, and Saints, realizing too that while these great men and women led extraordinary lives, they are not protected by infallibility either, and often taught on matters that the Church would not solemnly define until years or centuries later, and in some cases, may even have appeared to err greatly in matters that were already defined. Since the Ordinary Magisterium, Fathers, Doctors and Saints are able to and have erred, the faithful should, when deciding whether or not to adhere to one of their teachings, always cross-reference the higher authorities of Church, the dogmas, to make sure that it does not contradict them.

Pope Benedict XIV, Apostolica Constitutio, (# 6), June 26, 1749: "The Church’s judgment is preferable even to that of a Doctor renowned for his holiness and teaching."

This is especially important, since the devil has means at his disposal, whereby he might make his own doctrines appear to have come from the friends of God.

Revelations of St. Birgitta of Sweden, Book 2, Chapter 14 (on the words of God, spoken through His saints): "My enemy's second method is to use deception in order to make my gold look like clay. For this reason, when any of my words are being transcribed, the transcriber should bring two trusty witnesses or one man of proven conscience to certify that he has examined the docuмent. Only then may it be transmitted to whomever he wants, in order not to come uncertified into the hands of enemies who could add something false, which could lead to the words of truth being denigrated among simple folk."

http://www.catholic-saints.net/saints/st-bridget/st-bridget-of-sweden.php