But this creates no reason not to change if across books. I can pick up the MM and go whether or not it says the same thing as an earlier (or later) versions says.
For me the main reason it shouldn't generally change across books is if I run a game of D&D in 2017 and find that trolls in D&D are tall, lanky green things with pointy noses and powerful regeneration who hate fire and acid, and then I run a game of D&D in 2027 and trolls in D&D are warty, fleshy giants who turn to stone in sunlight and lurk under bridges, I can't use the new trolls in the same way I used the old trolls.
I can't, say, run this fun adventure I've had in mind for the last few years where a low-level party must cleverly use torches and bonfires to scare away a group of trolls that is far too powerful for them to fight directly. The old trolls don't exist in the new game anymore. I could
make 'em, but that's burden and grist and trouble and time and effort and there's still be some confusion to muddle through when I mention that the old sage knows that fire scares trolls away (a player who has read the 2027 MM is like "What? Trolls? Surely, the old sage is lying to us...perhaps he's a doppelganger!").
Why isn't that a fun story that D&D wants to help me tell anymore in 2027? What was wrong with the old story? Why are they telling me through their design that I shouldn't use the old story? Is there some problem with regeneration in 2027? Why should that story be harder to tell now than it was 10 years ago?
If I read LotR in 2027, it's gonna be the same text it was in 1997. The story of Sam and Frodo remain the same and be just as good as ever, but the story of Trolls in D&D must change and be entirely different now because someone in Renton figured this was a better story? Clearly, they didn't know about - or care about - the cool stories that you could tell with trolls in 2017!
TwoSix said:
The more interesting question, to me, is if 6e trolls are 9' tall, green, ride giant bats, and have innate regeneration that can only be stopped by freezing them, is that a good or bad change? It it bad purely because it is a change?
I mean, by all means, add in these trolls. You could even call 'em trolls, if you really wanted to (you know, Bridge Trolls, Mountain Trolls , Bat Trolls! Being completely different creatures haven't stopped Ogres and Ogre Magi from being smooshed together!). But, you don't have to get rid of the old trolls in the process. That negation is what gives the change most of its problems.
Because you don't have to obliterate that old story, to do so anyway can seem at the very least like pointless change for the sake of change. Even
spiteful if you're feeling especially wronged by it - like they went out of their way to destroy a perfectly good story just because they only want people to use the new one (like, if they described these new trolls as DRINKING AND SWIMMING IN ACID, because they love it so much!). Or like the 2027 designers just don't want you playing this new game, since they're not interested in supporting the stories you want to tell with it anymore. Why even bother to get invested in the game, if it doesn't want to support what
you want to do with it?