Perhaps one of the most common challenges raised by Roman Catholic and Orthodox apologists is this:
“How do you know that you have the correct canon of Scripture?” or “Who canonized the Bible, and when?”
These questions are often presented in debates, taken as though they expose a fundamental weakness in Protestant Bibliology. Roman Catholic and Orthodox proponents often assert that Protestants have borrowed or “piggybacked” off of tradition in order to establish their canon of Scripture. They assert that unless an infallible Church or Holy Tradition declares which books belong in the Bible, Protestants have no basis for knowing what Scripture actually is.