We evangelicals are proud of how we eschew tradition, bragging that we find our rule of faith in "sola scriptura" -- the Bible alone.
I love the way this sounds, the certainty with which I can mouth these sentiments. Until I remember that the specific books that make up the Bible were argued about for the first 2 centuries of the church's existence, and not finally agreed upon until into an ecumenical church council. And the books those church fathers determined we take from granted as Scripture, as God-breathed, inerrant, inspired.
In other words, it's our tradition to accept these books as canon.