Tradition

"Sacred Scripture is the speech of God as it is put down in writing under the breath of the Holy Spirit."

"And [Holy] Tradition transmits in its entirety the Word of God which has been entrusted to the apostles by Christ the Lord and the Holy Spirit. It transmits it to the successors of the apostles so that, enlightened by the Spirit of truth, they may faithfully reserve, expound and spread it abroad by their preaching."

As a result the Church, to whom the transmission and interpretation of Revelation is entrusted, "does not derive her certainty about all revealed truths from the holy Scriptures alone. Both Scripture and Tradition must be accepted and honored with equal sentiments of devotion and reverence." (Catechism of the Catholic Church, second edition)

Roman Catholics will often claim that the 'Early Church Fathers' back them up on absolutely every doctrine they hold (see here), but this is simply not true. They also claim that the traditions of the apostles have been passed down orally and have been preserved among their clergy (church leadership). However, if these traditions definitely contradict the Bible, any Christian must acknowledge that they are false.

By way of example, when the Pharasies' traditions contradicted scripture, Jesus rejected their traditions and clearly showed that they were serving the devil, rather than God (Matthew 15:1–9; Matthew 23:13–30; Mark 7:1–22).