Which Canon?

 "Canon" is a measuring rod. In the context of Christian literature, the Canon is the core set of writings by which all other writings and teachings are to be measured, AKA the Bible, and different sects of Christianity consider slightly different sets of books to be valid canon.

So, it seems like a valid question for skeptics to ask "Which canon?" when you talk about the reliability of the Christian Canon. But let's think that through... If Canon 1 contains 66 books, Canon 2 contains the same plus 5, and Canon 3 contains the same plus 10, the only sure, reliable canon among the three sets is the first and smallest. Everyone agrees on the contents of Canon 1, while many people believe that the extra books in Canons 2 and 3 contradict the contents of Canon 1. Of course, whether they do contradict or not can be a matter of opinion, but you won't go wrong by sticking with Canon 1. That doesn't mean that the books included in Canons 2 and 3 aren't inspired or valuable. It just means that Canon 1 is a universally recognized rod for measuring the reliability of extra-Biblical works, even those other books included in some sectarian Bibles.