Let me see if I can cover the idea of Sacred Tradition a little more thoroughly, since it is one of the more misunderstood aspects of the Catholic faith. Catholics DO hold the Bible to be the inspired Word of God and above all other writings, of course. However, for much of the early Church, Christians did not have access to the Bible. Much was taught through oral tradition. In fact, large parts of the Bible are simply oral traditions written down. There was much disagreement in the early church as to what actually constituted Holy Scripture. Some documents, like the Didache, Epistle of Barnabas, the Letters of Clement, and even the Gospel of Thomas were considered for inclusion and used in some regions by early Christians. Others, like 2 Peter and Revelation, were almost not included. This disagreement continued until a decision was made by the Catholic Church to finally determine which scriptures could definitively be considered inspired. The Councils of Carthage and Hippo in the late 300s AD, later reinforced by statements made by the pope, finally settled the matter. But up until that point, communities did not have complete access to ALL of the scriptures in all places. Even if they did, the Old Testament was in Hebrew, and the New Testament was in Greek and Aramaic. Few could read both languages. People still needed to learn about Christianity through oral tradition. The first widespread version of the Bible in a single language was the Latin Vulgate penned by St. Jerome in the mid 400s. So, for over 20% of Christianity, there WAS no Bible, per say. Even once the Vulgate was completed, Rome fell soon after, and for several hundred years, the literacy rate in Europe remained under 1%. This is also why Catholic Churches tended to have statues and stained glass windows, so that parishoners could learn about Christianity orally and pictorally.
With regards to the beliefs of the Catholic Church, the Church will ALWAYS look to the Bible first. However, we also know that there are concepts that were believed and followed by early Christians that are not included in the Bible. (For example, the scriptural evidence for the Trinity is not very explicit. Sacred Tradition fills in much of the gaps in our understanding there.) The Catholic Church also looks to what the consensus of belief was in the early Church, as spelled out by the Early Church Fathers in their writings. If a belief has been held by the Early Church, and has remained constant over time, then it cannot be changed by the Catholic Church. Those things that cannot be changed by the Church are called Dogmas (a theological point that is also shared by the Orthodox Church, I might add). Now, some traditions can be changed, and these are generally called disciplines. An example of a discipline would be priestly celibacy. Although celibacy is a tradition of the Latin west, at times in the past married priests were permitted, and they still are among ministers of some other faiths that convert to Catholicism, and in Eastern Catholic Churches. Dogmas do NOT have to be proclaimed as such. Dogmas are usually only specifically defined if they are challenged by outside groups. The Council of Trent defined dogmas that were challenged during the Protestant Reformation, and the dogmas of the Immaculate Conception and Assumption were proclaimed by special ex-cathedra statements of the pope in the nineteenth and twentieth centuries. (Neither of which are to be found explicitly in the Bible, I might add.)
So, dogmas are the very things that minimally define Catholicism. Once they are proclaimed, they cannot be changed, even by the pope. For example, no pope could ever un-proclaim the Trinity. If any dogma were to change, it would throw into question every other dogma of the Catholic Church, and the Church would fall. The Catholic Church believes, as a dogma, that for the miracle of transubstantiation to occur, it requires real wheat bread and real grape wine, even if the wheat content is minute. It also requires the valid words of institution (i.e., This is my Body, This is my Blood…). The unfortunate consequence of this is that there is nothing that even the pope can do to change this belief. The Catholic Church considers it a sign that it’s belief is protected by the Holy Spirit that its dogmas have remained utterly unchanged since the time of the Apostles.
