a belief or a way of thinking that is accepted as true or correct
I also thought of tacit assumptions and presuppositions if orthodoxy is a word too strong for what you're seeking.
The mild connotation of orthodox would be the antonym of unorthodox. That is, orthodoxy is the usual beliefs, while anything unorthodox is an unusual belief. I say that orthodox may seem too strong because it carries a meaning akin to fundamentalist in some regards.
Similar is canon/canonical.
