“Ask a thoughtful Protestant about where Protestantism and Catholicism most significantly diverge, and it is likely that he will mention the closely related areas of tradition and authority. Now, Protestants tend to be very suspicious of any talk of tradition as playing a role in theology, as it would seem to stand somewhat in tension with the Reformation’s view of Scripture alone as the authoritative basis for theological reflection. In fact, the Reformation itself represented a struggle over two types of tradition, that which scholars call T1, tradition based on Scripture as the sole source of revelation (the position of Protestants such as Luther and Calvin, and some pre-Tridentine Catholics), and that which they term T2, tradition based on two sources, namely, Scripture and an oral tradition mediated through the teaching magisterium of the church. This latter was arguably the position codified at the Council of Trent, although it would seem that the boundary between T1 and T2 is in practice often blurred, and very difficult to define in any formal or precise sense; nevertheless, as a heuristic device the distinction is useful, and it is really only as Protestants come to understand exactly what is the Catholic view of tradition (i.e., T1 plus T2) that they can come to properly understand how tradition (T1) does not subvert the notion of Scripture alone.
A moment’s reflection on Protestant practice should demonstrate the truth of this. Every time a Protestant minister takes a commentary off his shelf to help with sermon preparation, or opens a volume of systematic theology, or attends a lecture on a theological topic, he practically acknowledges the importance of T1, whether he cares to admit it or no. A belief in Scripture as a unique and all-sufficient cognitive foundation for theology does not, indeed, cannot, preclude the use of extrabiblical and thus traditional sources for help. Protestantism and Catholicism both value tradition; the difference lies in the source and authority of this tradition: Protestant tradition is justified by, and is ultimately only binding insofar as it represents a synthesis of the teaching of the one normative source of revelation, holy Scripture.”
– Carl Trueman, Fools Rush In where Monkeys Fear to Tread: Taking Aim at Everyone, p. 151-153