Some answers here suggest I'm not getting my question across. This statement in another thread prompted this thread:
in a world with concrete alignment and a guaranteed afterlife
. . .
you know for a fact that when killed an evil creature heads off to one of the evil planes to become anything from sustenance for demons to a demon itself
I've seen this concept mentioned many times over the years, around here.
This idea that people in a D&D world "know" as "fact" that there is an afterlife, there are other planes to which their souls go for reward or punishment. That the gods are real and active.
My question was not based on how do people believe this stuff, but how can they know it for fact?
The discussions on how raise dead-type spells would change a world -- politically, religiously, etc. -- always start with the basic concept of "everyone knows for a fact" how the game rules [spells] work. My point on this is that only the Players sitting around the table know these "facts" because they've read the rule books. The normal people in the game world don't have the mechanics of the universe written down and published for all to read.
Considering how truly rare high-level clerics are (compared to the general population, not compared to PC demographics), and how much such magics cost, the vast majority of people have never had any direct experience with the "realness" of gods, planes, afterlife, and return to life.
I'd even say that the average person doesn't even have an understanding of the alignments. If someone said, "Old Man Jed is Chaotic Neutral," no one would understand what that meant.
So, how can the existance of gods, planes, afterlife, (and alignment, among other things) be commonly known facts in a D&D world? The high-level cleric comes around to town and offers to cast planeshift for the gathered folks? "I can take you to my god right now!"
Yeah, how many folks are gonna take that trip?
Bullgrit