The Catholic Church bases her teaching upon one source: The word of God. This divine revelation is transmitted in two ways: through Scripture and apostolic tradition. Many assume that only the writings of the apostles are the word of God. However, their oral transmission of the faith is also considered the word of God (1 Thess. 2:13). Few Protestant groups today accept the validity, let alone the authority, of tradition. In fact, many believe that Scripture is the only definitive source of divine truth.
"I protest that I do not intend to assert or determine anything that has not been manifestly determined by Sacred Scripture or by the authority of the Church. Wherefore I submit all I have said or shall say to the correction of Holy Mother Church and of all learned men."