Thanks for bringing the conversation here.
Originally Posted by 1337 b4k4
In that case, your DM should be providing the information. It's no different than the DM describing the smell of the room, or the dampness of the air. The DM's job is to provide the information to the players that they need to know and should know to make informed choices. Besides, if the players don't know to ask for the knowledge, having a knowledge roll isn't going to help them at all, since they won't know to roll for it.
There is a point to this, such as Knowledge Arcana. Making the roll could be considered just an excuse for the DM to tell the player what some magical effect is. However, Knowledge checks serve two important functions:
1) It was common, at least in my experience over several DMs and years of playing, pre-3E for the DM to often say "You just don't know" whenever the player asks about something. DMs flat-out refused to give information until they see fit at their convenience. Knowledge checks became the game mechanic method for arbitrarily saying this PC knows something, tell him already DM. Years of post-3E play of DM telling players stuff because of rolls has diminished this problem. "You just don't know" has become an honest true legitimate "You don't know" instead of its former condescension with "just".
2) On the DM side, DMs often complain about PCs metagaming combat because they've read the Monster Manual. DMs had to fight back by changing monsters, such as trolls wearing rings of fire resistance or be a variant troll that's vulnerable to cold and electricity instead of fire and acid. Knowledge checks became the game mechanic method for arbitrarily saying this PC knows about this monster and the player is permitted to use his personal knowledge for the combat. Fail the check, the PC does not know and the DM is in his rights to metaphorically slap the hand of a player using metagame knowledge in the combat. The complaint of 3E warrior/spellcaster differences on being able to make this check is a fault against the mechanics of the concept, not the concept itself. Knowledge Devotion is an important feat to some. This metagame issue is not going away. Some method is needed.
As for players not knowing to ask, that is when the DM should either fiat tell the player his character knows this or ask for the Knowledge check if there's a chance the PC doesn't. That's DM-style issue, but I would like the 5E DMG to recommend it.