This question is a little like asking, "To whom must I listen: my mother or my father?" For those who view scripture and tradition to be separate—or even in opposition, the answer may be surprising. “Sacred tradition, sacred scripture, and the teaching authority of the church,” says Dei Verbum, the Second Vatican Council’s document on divine revelation, “are so linked and joined together that one cannot stand without the others.”

Let me ask the question in another way: Which came first, scripture or tradition? Our impulse is to answer, "Scripture, of course!" But in reality, tradition did. Where did scripture come from, after all? Centuries of prophets, sages, and evangelists wrote down the community's experience of God as it unfolded through revelation, ritual, and history. Lots of things got recorded, many of which are not included in our Bible today.

Which brings us to the second level of tradition: Some group of people had to sift through piles of traditions to determine which would be included in the "canon" of scripture (authoritative texts) and which would not be binding on the community for the future. Jewish teachers made that determination for the documents known as the Hebrew Bible or Old Testament. A later group of Christian leaders made that decision for what would become the New Testament. As Dei Verbum puts it, “Through . . . tradition the church's full canon of the sacred books is known.”

So in a nutshell, teachings became traditions and were later selected by leaders whose authority itself was determined by tradition. These leaders in turn shaped the scriptures we have today. In the most meaningful sense, then, scripture is the very heart of tradition.

To separate scripture from tradition as if they were alien concepts is to misunderstand the origin of scripture. If the Bible had dropped from the sky as is, cover to cover, you could talk about scripture as your sole authority. But without tradition, there would be no scripture, and the reading of scripture itself has contributed to ongoing development of tradition.

Scripture
Luke 4:16-21; John 1:1-5, 14; 1 Thessalonians 5:19-21; Hebrews 1:1-3; 4:12

Church document
The Dogmatic Constitution on Divine Revelation (Dei Verbum) of the Second Vatican Council

Book
Scripture in the Tradition: Milestones in Catholic Theology by Henri de Lubac (Crossroad)