D&D 5E How to Handle Monster Knowledge Checks

[AaronOfBarbaria]

I kinda agree with you in principle. However.

As DM how would you react to a character with no background on the subject, pulling out a crossbow bolt and blessing it in order to kill a rakshasa*, a creature they had done no research on, or had never encountered?

(in the contex of when rakshasa could be instantly killed that way)

I'm with iserith and Brad on this, but I have a further questions because this is one of those instances I frequently mention happening as a result of the DM being concerned about the wrong thing:

Does the character need to know that the creature before them is a rakshasha in order to choose to bless something?
Does the character need to know that the creature before them is a rakshasha in order to choose to use a crossbow?
Does any character need to be certain of the outcome of any action in order to choose to attempt it?

Because if the answer to all 3 of those questions are not "Yes, unquestionably" then you have (even if unintentionally) stepped into the territory of trying to police the thoughts of your player - Because if this is a guess or a whim for them, like it clearly is for the character because they have no background on the subject, the action would be acceptable, but if they know even though their character is making a guess or following a whim the action suddenly becomes unacceptable.

 

[Ilbranteloth]

I'm sure you see it differently, but the thought I'm having is that you aren't requiring enough of your players from my perspective. As much as I usually think it's my job to make the play experience enjoyable for them, examples like that just make me think that players need to accept some responsibility for the overall experience (not just their character). Part of that, in my opinion, is playing the game by established parameters (and keeping player knowledge and character knowledge separate ought to be a perfectly acceptable parameter if it enhances the game for the players (including the DM)).

Using obscure lore that the character doesn't have any way of knowing is just childish and unacceptable behavior. It is literally the kind of crap you expect from a child. But with a child I would be more patient and help them learn that's not how we do it because of such and so. If an adult did that, I would explain the issue once and not be patient if it happened a second time.

I'm not sure I would consider it childish and unacceptable unless you had explicitly told them before that it is lore they would not know.

Is the rule at your table that they don't know any unique vulnerabilities of a monster they've never met. I've seen those tables and they make even less sense to me. If humans have been fighting trolls for thousands of years, wouldn't every human culture in a region where trolls are a threat know what is needed to defeat them?

So if the answer is that the PCs will know the vulnerabilities of some of the monsters, then someplace you need to make it known that there are guidelines to which vulnerabilities your characters don't know. Unless this is made clear to start, it's hard to fault somebody for stepping over a line.

Simply declaring player knowledge and character knowledge is not an acceptable parameter. It's too broad. Otherwise the players will spend an inordinate amount of the session trying to determine what their character knows or not.

Coming out the woods you see 6 goblins and 3 wolves.
Do I know what a wolf is?
Of course, they are common in this world.
Do I know what a goblin is?
Of course, they are common in this world.
OK, I'll go see if the goblin would like to join us on our quest. Or do I know that goblins are evil monsters?

Sure, it's absurd. But you have to establish the line before you can condemn somebody from crossing it. If you determine that they don't know certain things, I think it's also helpful for some guidelines on how to handle it when you know something your character doesn't. Because roleplaying experimentation when you already know the answer can get a little weird.

Hmm. My sword didn't seem to bother that rat-man very much.
Ouch.
Maybe it wasn't as good a shot as I thought.
Ouch.
Hmm. What about my mace?
Ouch.
Run away. Those aren't working, how about my bow, at least it can't reach me then.
It's still coming?
Well, I've got these crappy arrows I found with the silver tips. Not very sharp, but maybe I can slow it down if it thinks they're nice and shiny.

 

[Sword of Spirit]

I think it would be more reasonable to say that I require more of the DM. And, as the DM in this discussion, requiring more of myself is likely to get better results since I cannot control other people. I can control whether or not I alter monsters when playing with veterans. And if I don't, I hardly have any room to complain in my view when the players reduce the difficulty of a challenge by applying their hard-won knowledge to the situation.

Knowledge gained through out of character means isn't hard won in character knowledge. It also trivializes the in character stats that might allow a less knowledgeable player to have a more knowledgeable character. IA new player trying to play a loremaster who knew little more than what the DM provided (either automatically or as a result of rolls) might validly feel slighted when the rest of the party are playing characters who should have much less knowledge than his, but end up implementing a lot more because of the players' knowledge.

Also, for myself and every other GM I know, we put more (often way more) work into the experience than any of the players. Asking them to keep their player lore-knowledge separate from character-lore knowledge isn't really asking for much.

To you. To me, it's unacceptable to demand other people play a certain way when I could have fixed this issue myself with the stroke of a pen prior to it becoming a problem.

Sure, if your setting is mutable and lacks a set history. If it does, it is an imposition on the DM's world to change rakshasa's (etc) function just because a player can't be bothered to role-play in character--and that is what we are talking about. We aren't talking about a player having a valid difference of opinion from the DM on what his character would know. We are talking about a player knowing his character reasonably shouldn't know something and choosing to implement it anyway.

I'm going to bring up something that I think talk on ENWorld often fails to present the reality on. Maybe I'm misinterpreting what people are presenting, but here is what I see:

Disagreements about many of these sorts of things often come down to an assumption that players want narrative world control. That acting within parameters that keep their area of control firmly on their character with that character's attributes is a chain binding them down that they are chafing against because it doesn't let them do cool things and play the way they really want to play.

Hogwash.

Sure, I have no doubt that some players feel exactly that way. And I don't fault them for it. I don't even think it's necessarily about immaturity. It can also simply be a playstyle they are going for, a collaborative, narrative-focused style where they want a hand in shaping the world, and they as a player want some control over what happens outside of control that their character would have. I run that sort of stuff outside of D&D, and I even have a defined mechanic (and expansion of the Inspiration system) that I use to allow that in D&D in a limited sense.

But that is by no means the only attitude for players to have. I know that often when I am a player, I actually feel cheated if the DM is running the world that way! I want to interact with a "living world", and in order to interact the world has to have an independent existence (in this case that is in the DM's head and in his notes/books/etc). If I am creating a world I am not interacting with it--at least not in the same way. Do you get the same experience reading a story you wrote yourself as reading one that someone else wrote? Nope. It feels quite different. And a lot of time when I'm playing an RPG (and D&D in particular) I want the feeling of playing in something I had no hand in creating and have no ability to affect other than through the avatar with which I am interacting with it--my character. I'm not the only one who enjoys playing that way.

So while I'm not accusing any individuals in particular of this, I just want to make it clear that the idea that players are going to feel bad if they aren't given control over things outside their character isn't necessarily true. Some players feel bad if the DM doesn't hold his world consistent and unaffected by player narrative control or out of character interests.

I'm not sure some people have ever considered that possibility. If you've only ever played with narrative control-desiring players, then maybe it's a foreign idea, but it's a real thing. This isn't some sort of mean controlling no fun DM power trip thing.

I'm with iserith and Brad on this, but I have a further questions because this is one of those instances I frequently mention happening as a result of the DM being concerned about the wrong thing:

Does the character need to know that the creature before them is a rakshasha in order to choose to bless something?
Does the character need to know that the creature before them is a rakshasha in order to choose to use a crossbow?
Does any character need to be certain of the outcome of any action in order to choose to attempt it?

Because if the answer to all 3 of those questions are not "Yes, unquestionably" then you have (even if unintentionally) stepped into the territory of trying to police the thoughts of your player - Because if this is a guess or a whim for them, like it clearly is for the character because they have no background on the subject, the action would be acceptable, but if they know even though their character is making a guess or following a whim the action suddenly becomes unacceptable.

I see nothing wrong with a character making an appropriate guess. When I'm a player, I will often make an Intelligence check by myself just to decide it my character would know something I'm unsure of.

"Dang it, nothing seems to be working against this fiendish monster! Priest, try casting bless on the rogue's crossbow or something, while we try to grapple and tie up the thing." It would be a stretch, and we'd all know that out of character knowledge is involved, but once in a blue moon it would be worth a laugh.

I'm not sure I would consider it childish and unacceptable unless you had explicitly told them before that it is lore they would not know.

Is the rule at your table that they don't know any unique vulnerabilities of a monster they've never met. I've seen those tables and they make even less sense to me. If humans have been fighting trolls for thousands of years, wouldn't every human culture in a region where trolls are a threat know what is needed to defeat them?

I assume things like fire for trolls and silver for lycanthropes is pretty common knowledge in a typical D&D culture. I'm also negotiable on those things. If a player brings up something that they OOC think should be common IC knowledge, I usually end up agreeing with them (maybe it helps that my players generally provide solid justifications).

So if the answer is that the PCs will know the vulnerabilities of some of the monsters, then someplace you need to make it known that there are guidelines to which vulnerabilities your characters don't know. Unless this is made clear to start, it's hard to fault somebody for stepping over a line.

I wouldn't fault someone for incorrectly guessing where a line is. I would fault them for intentionally flaunting my generous interpretations by using something they themselves don't believe that their character would know. Fortunately, with my group it's probably more likely that I would tell them, "your character would know X" when they didn't think they would than the reverse.

Simply declaring player knowledge and character knowledge is not an acceptable parameter. It's too broad. Otherwise the players will spend an inordinate amount of the session trying to determine what their character knows or not.

Each player gets a brief document telling them what their character knows in general terms.

Here's an example paragraph from one character's primer: "You are familiar with certain types of monstrous creatures that roam the world. You understand the nature of the undead. You also are aware of the existence of elemental creatures and magical constructs, as well as knowing that more bizarre creatures dwell out there."

From another character: "You also have a basic understanding of various other races of the world, dwarves, orcs, etc, as well as monstrous species such as dragons or giants. You know the difference between good and evil dragons, and that their breath's vary, and you have heard of the five types of true giants. You understand the changing of the seasons, and can identify all common plants and beasts. In addition, you are familiar with basic truths about the fey. You know about those who have come back from the grave—the undead. A variety of types exist, and you have a better chance than most of knowing the difference..."

While it's nice to role-play the elf telling the human something new about a creature they have just spotted, we don't really have the time to play out the character's lives in real time. So much of that is glossed over as knowledge that is shared at a meal at a campfire, or over an ale at a tavern.

I like this thought. Sometimes my players like playing out in-character discussions about their past and the things they know, so assuming more of those have happened is a great idea.

The thing that I'm being critical of, and feel that it is ill-advised for DM's to encourage, is players actively using knowledge that they themselves do not believe that their characters would know.

 

[iserith]

Knowledge gained through out of character means isn't hard won in character knowledge.

It's hard-won by the players. They earned it in my view and, just like in any other game, I think they should be free to use it, if they so choose. It's not for me to tell them they can't.

It also trivializes the in character stats that might allow a less knowledgeable player to have a more knowledgeable character. IA new player trying to play a loremaster who knew little more than what the DM provided (either automatically or as a result of rolls) might validly feel slighted when the rest of the party are playing characters who should have much less knowledge than his, but end up implementing a lot more because of the players' knowledge.

I don't think there's any particular reason to believe a character "should" know less than the "loremaster." It's very easy to imagine, for me at least, why someone might know more about a particular subject that this learned scholar. And, again, if you want to make sure the player of the loremaster gets to dominate that particular niche, you can just change the monsters instead of asking or demanding players change how they play. That is a way more reliable strategy in my view then relying on others to adhere to a pretty arbitrary standard of what a given character knows.

Also, for myself and every other GM I know, we put more (often way more) work into the experience than any of the players. Asking them to keep their player lore-knowledge separate from character-lore knowledge isn't really asking for much.

I don't think however much work I put into my game justifies asking the players to do that. That seems like a rather entitled attitude to have and I just can't share it. But it's very enlightening as it could well be the root cause for why it appears to stick in your craw to have to change your monsters. "Why should I have to do that on top of all the other 'work' I'm doing for these ingrates?"

Sure, if your setting is mutable and lacks a set history. If it does, it is an imposition on the DM's world to change rakshasa's (etc) function just because a player can't be bothered to role-play in character--and that is what we are talking about. We aren't talking about a player having a valid difference of opinion from the DM on what his character would know. We are talking about a player knowing his character reasonably shouldn't know something and choosing to implement it anyway.

I've given examples about how easy it is to justify how a character knows something. It might even be easier than justifying why they don't since we're talking about a fictional world and fictional characters.

Further, if you really must keep the monsters the same (you don't, but whatever), then here's another option: Make having the knowledge be useful, but implementing strategies based on it hard, costly, complicated, or dangerous. Sure, go ahead and use fire on those trolls - but their lair is in a swamp filled with pockets of explosive gas. Strike that match at your own risk.

I'm going to bring up something that I think talk on ENWorld often fails to present the reality on. Maybe I'm misinterpreting what people are presenting, but here is what I see:

Disagreements about many of these sorts of things often come down to an assumption that players want narrative world control. That acting within parameters that keep their area of control firmly on their character with that character's attributes is a chain binding them down that they are chafing against because it doesn't let them do cool things and play the way they really want to play.

Hogwash.

Sure, I have no doubt that some players feel exactly that way. And I don't fault them for it. I don't even think it's necessarily about immaturity. It can also simply be a playstyle they are going for, a collaborative, narrative-focused style where they want a hand in shaping the world, and they as a player want some control over what happens outside of control that their character would have. I run that sort of stuff outside of D&D, and I even have a defined mechanic (and expansion of the Inspiration system) that I use to allow that in D&D in a limited sense.

But that is by no means the only attitude for players to have. I know that often when I am a player, I actually feel cheated if the DM is running the world that way! I want to interact with a "living world", and in order to interact the world has to have an independent existence (in this case that is in the DM's head and in his notes/books/etc). If I am creating a world I am not interacting with it--at least not in the same way. Do you get the same experience reading a story you wrote yourself as reading one that someone else wrote? Nope. It feels quite different. And a lot of time when I'm playing an RPG (and D&D in particular) I want the feeling of playing in something I had no hand in creating and have no ability to affect other than through the avatar with which I am interacting with it--my character. I'm not the only one who enjoys playing that way.

So while I'm not accusing any individuals in particular of this, I just want to make it clear that the idea that players are going to feel bad if they aren't given control over things outside their character isn't necessarily true. Some players feel bad if the DM doesn't hold his world consistent and unaffected by player narrative control or out of character interests.

I'm not sure some people have ever considered that possibility. If you've only ever played with narrative control-desiring players, then maybe it's a foreign idea, but it's a real thing. This isn't some sort of mean controlling no fun DM power trip thing.

It isn't about narrative control. It's about a player declaring actions for his or her character and nothing more which is their only role in the game. You appear to want to say certain actions are simply invalid because a character couldn't possibly attempt it due to a lack of knowledge established by some arbitrary standard. I don't agree with that and whatever bad outcomes you think may come from allowing them to do as they wish is easily mitigated with a couple of techniques that I've mentioned in this post.

 

[SkidAce]

It isn't about narrative control. It's about a player declaring actions for his or her character and nothing more which is their only role in the game. You appear to want to say certain actions are simply invalid because a character couldn't possibly attempt it due to a lack of knowledge established by some arbitrary standard. I don't agree with that and whatever bad outcomes you think may come from allowing them to do as they wish is easily mitigated with a couple of techniques that I've mentioned in this post.

What if a player declares actions for his character that leads him past all the traps and straight to the goal of the dungeon?

If I'm following ya'll that would be just as okay as the rakshasa example. (The PLAYER had knowledge of the monster the CHARACTER didn't/The PLAYER had knowledge of the module/dungeon that the character didn't).

Either way, thanks for the discussion, like I said this is not a current/nor past problem for any groups I've been in, so it was more of a "hmmmmm" thing after reading the thread.

GAME ON!

 

[AaronOfBarbaria]

...new player trying to play a loremaster who knew little more than what the DM provided (either automatically or as a result of rolls) might validly feel slighted when the rest of the party are playing characters who should have much less knowledge than his, but end up implementing a lot more because of the players' knowledge.

There is an easy fix for that problem, which is actually a player etiquette problem, not one of using knowledge inappropriately.

The fix being that the more knowledgeable players could be making the new player feel included, rather than slighted, by feeding the knowledge they want to act upon to the new player, along the lines of "Ooh, maybe your character would be able to tell us all how BLAH these BLIBBITY BLAH creatures BLAH?" Because the actual problem is that the established players are playing despite the new player, rather than playing with the new player.

Also, for myself and every other GM I know, we put more (often way more) work into the experience than any of the players.

Have you tried scaling it back and just having some off the cuff fun? Most of my campaigns that my players have given stellar reviews to were run with me putting equal, or even less, "work" into the experience than the players. Maybe it'd work for you too.

This isn't some sort of mean controlling no fun DM power trip thing.

It isn't, but it can easily, even accidentally, become a controlling no fun DM power trip thing. As soon as it goes to that point where a player is being denied the ability to role-play their character as making a guess or acting on a whim because the DM knows the player isn't guessing or acting on a whim, it's become a controlling no fun DM power trip thing as it has prevented the player from playing their character as they choose to.

I see nothing wrong with a character making an appropriate guess. When I'm a player, I will often make an Intelligence check by myself just to decide it my character would know something I'm unsure of.

I'm fine with player-elective rolls like that; it's the player choosing to let a die decide between actions they have thought of in the moment.

What I'm not fine with is a DM stepping in and telling a player how they must play their character, including doing so by questioning why I as a player chose an action rather than asking for the reason why the character chose that action.

It would be a stretch, and we'd all know that out of character knowledge is involved, but once in a blue moon it would be worth a laugh.

I don't think that I have ever heard of a campaign in which these types of situations could possibly come up more frequently than "once in a blue moon" that was not a campaign wherein the DM was deliberately attempting to trick their players with "Gotcha!" challenges or was attempting to make the game basically unplayable on purpose by using challenges that could not be defeated without certain knowledge that was intentionally withheld from the player characters. So I don't think there is actually a problem with frequency of this kind of "my character guessed correctly the information I clearly already knew" moment in a typical campaign.

The thing that I'm being critical of, and feel that it is ill-advised for DM's to encourage, is players actively using knowledge that they themselves do not believe that their characters would know.

I think the easiest thing to do is convince the players that it is okay for them to not even think about whether their character does or doesn't know something - just do what feels right and fun at the moment, and nobody is going to question you.

But then, that's because I think the hesitation that is "I'm don't think my character would know..." is primarily caused by belief that they are going to figuratively get their knuckles wrapped with a ruler for stepping out of line, by way of the DM demanding an explanation for why their adventurer just did something adventurous. And I find that making it clear to all involve that the environment is not hostile in that way, it's a safe place to unwind and have some fun with some friends, no judgements, no hurt feelings (at least not so hurt that another tasty beverage or scrumptious snack won't make it all better) is a significant tool in a DM's fun-experience-building tool kit.

 

[Ilbranteloth]

Knowledge gained through out of character means isn't hard won in character knowledge. It also trivializes the in character stats that might allow a less knowledgeable player to have a more knowledgeable character. IA new player trying to play a loremaster who knew little more than what the DM provided (either automatically or as a result of rolls) might validly feel slighted when the rest of the party are playing characters who should have much less knowledge than his, but end up implementing a lot more because of the players' knowledge.

I get what you're saying here, but, much like 5e, why not approach it as a baseline with bonuses, instead of a baseline that has both penalties and bonuses.

For example, there used to be a non-proficiency penalty. Now you gain a bonus if you have proficiency, not bonus if not. And it goes up from there.

In which case the baseline is what's in the MM and what all the players know, and as the DM you add additional goodies for the loremaster. That way the loremaster character and player both feel the benefit of having a better skill. You can even go beyond this, so that your loremaster not only has the opportunity to use their skill to gain more information within the game, but you can provide them actual lore that they can have access to outside of the game so they player actually knows lore about your campaign that only you and they know.

 

[iserith]

What if a player declares actions for his character that leads him past all the traps and straight to the goal of the dungeon?

Isn't that what the players try to do all the time whether they have the knowledge or not?

 

[AaronOfBarbaria]

What if a player declares actions for his character that leads him past all the traps and straight to the goal of the dungeon?

Unless it is literally impossible for his character to have done just that, why should I be bothered that a dungeon which obviously could have its threats bypassed has done just that?

Where I might be concerned is if the group playing is not enjoying that they keep moving toward their goal without setback, but that has nothing to do with what the players do or don't know, and is easily fixed by improvising a setback in a form they can't simply bypass.

And for what it is worth, I have run published adventures multiple times and as a result had some of the players in some of the groups going through them have played them before, and still had the groups all have fun. The key being that I didn't try to police what the repeat players did or didn't do, and none of the players were actively trying to ruin the fun for anybody, them selves included.

 

[Ilbranteloth]

Also, for myself and every other GM I know, we put more (often way more) work into the experience than any of the players. Asking them to keep their player lore-knowledge separate from character-lore knowledge isn't really asking for much.

So I agree that there are times where this is quite important (such as somebody who might have read, played, or even run a published adventure that you are using). And i would totally agree that if you are selecting a published adventure, and somebody goes out and reads it, that's just plain wrong. It really ruins their fun more than anything, but it can impact the fun of others.

Sure, if your setting is mutable and lacks a set history. If it does, it is an imposition on the DM's world to change rakshasa's (etc) function just because a player can't be bothered to role-play in character--and that is what we are talking about. We aren't talking about a player having a valid difference of opinion from the DM on what his character would know. We are talking about a player knowing his character reasonably shouldn't know something and choosing to implement it anyway.

I used to think that the MM lore was as sacrosanct as the adventure I was running, right down to trolls and fire. I was wrong. I've mentioned the main reason why I think that several times. People who live where real trolls exist will know what trolls are vulnerable to. More importantly, what is the benefit from a game perspective? A single encounter where they don't know the secret and then learn it? Usually that's all it amounts to. And for that 15 minutes acting like you don't know the answer.

I'm going to bring up something that I think talk on ENWorld often fails to present the reality on. Maybe I'm misinterpreting what people are presenting, but here is what I see:

Disagreements about many of these sorts of things often come down to an assumption that players want narrative world control. That acting within parameters that keep their area of control firmly on their character with that character's attributes is a chain binding them down that they are chafing against because it doesn't let them do cool things and play the way they really want to play.

Hogwash.

Sure, I have no doubt that some players feel exactly that way. And I don't fault them for it. I don't even think it's necessarily about immaturity. It can also simply be a playstyle they are going for, a collaborative, narrative-focused style where they want a hand in shaping the world, and they as a player want some control over what happens outside of control that their character would have. I run that sort of stuff outside of D&D, and I even have a defined mechanic (and expansion of the Inspiration system) that I use to allow that in D&D in a limited sense.

But that is by no means the only attitude for players to have. I know that often when I am a player, I actually feel cheated if the DM is running the world that way! I want to interact with a "living world", and in order to interact the world has to have an independent existence (in this case that is in the DM's head and in his notes/books/etc). If I am creating a world I am not interacting with it--at least not in the same way. Do you get the same experience reading a story you wrote yourself as reading one that someone else wrote? Nope. It feels quite different. And a lot of time when I'm playing an RPG (and D&D in particular) I want the feeling of playing in something I had no hand in creating and have no ability to affect other than through the avatar with which I am interacting with it--my character. I'm not the only one who enjoys playing that way.

So while I'm not accusing any individuals in particular of this, I just want to make it clear that the idea that players are going to feel bad if they aren't given control over things outside their character isn't necessarily true. Some players feel bad if the DM doesn't hold his world consistent and unaffected by player narrative control or out of character interests.

I'm not sure some people have ever considered that possibility. If you've only ever played with narrative control-desiring players, then maybe it's a foreign idea, but it's a real thing. This isn't some sort of mean controlling no fun DM power trip thing.

This doesn't apply to me, because frankly I find it's harder to find players that want to be part of a shared-narrative design. But, a lot of the more modern RPGs make this the central focus of the design, and to a number of people, seems to be considered a more evolved form of RPG. YMMV.

I see nothing wrong with a character making an appropriate guess. When I'm a player, I will often make an Intelligence check by myself just to decide it my character would know something I'm unsure of.

"Dang it, nothing seems to be working against this fiendish monster! Priest, try casting bless on the rogue's crossbow or something, while we try to grapple and tie up the thing." It would be a stretch, and we'd all know that out of character knowledge is involved, but once in a blue moon it would be worth a laugh.

This tends to work best if you are playing with a group that prefers (and is good) with the acting style of role-playing. Of course, there are some purists as well. The AD&D DMG suggested (potentially jokingly, it's hard to tell with Gygax some time), severe penalties for those that dare read anything other than the approved player books.

I assume things like fire for trolls and silver for lycanthropes is pretty common knowledge in a typical D&D culture. I'm also negotiable on those things. If a player brings up something that they OOC think should be common IC knowledge, I usually end up agreeing with them (maybe it helps that my players generally provide solid justifications).

I wouldn't fault someone for incorrectly guessing where a line is. I would fault them for intentionally flaunting my generous interpretations by using something they themselves don't believe that their character would know. Fortunately, with my group it's probably more likely that I would tell them, "your character would know X" when they didn't think they would than the reverse.

Each player gets a brief document telling them what their character knows in general terms.

Here's an example paragraph from one character's primer: "You are familiar with certain types of monstrous creatures that roam the world. You understand the nature of the undead. You also are aware of the existence of elemental creatures and magical constructs, as well as knowing that more bizarre creatures dwell out there."

From another character: "You also have a basic understanding of various other races of the world, dwarves, orcs, etc, as well as monstrous species such as dragons or giants. You know the difference between good and evil dragons, and that their breath's vary, and you have heard of the five types of true giants. You understand the changing of the seasons, and can identify all common plants and beasts. In addition, you are familiar with basic truths about the fey. You know about those who have come back from the grave—the undead. A variety of types exist, and you have a better chance than most of knowing the difference..."

The thing that I'm being critical of, and feel that it is ill-advised for DM's to encourage, is players actively using knowledge that they themselves do not believe that their characters would know.

So what I think this best illustrates is this: First, your objection (as stated twice here) is when the player acts on information that they don't think their character would have. Yet you also seem to object to when they act on information that you (the DM) think they shouldn't know either. I agree with you that for whatever the character is going to do, the more the player can explain and support that, the more likely I am to allow it (such as a clever social interaction). But if one of your players felt they knew something, you disagreed, and they couldn't make their case, it would be a problem (it seems).

The reality is really pretty simple, though: some players and DMs appreciate the challenge(?) of keeping character and player knowledge separate. If the rules are clear at your table, and particularly if you are playing with a group that agrees (which is not unusual since like-minded players tend to filter themselves into a particular DMs group), then it's the right option for you.

In the groups that do feel that way, i tend to find they are a bit too restrictive in what they think is "reasonable" for a character to know. I was one of them. It's not wrong to enjoy this, and if it's enjoyable, then go for it.

At this stage, I'm of the opposite mind. One of the reason I love the Forgotten Realms is that with so much material published, players can (if they choose) be very immersed in the world. There's shared lore and I want them to read more of it, not less. Much like you can start a Star Wars campaign on Tatooine and you don't have to mention that there are two suns, or that the planet is a desert, or what a sand person or jaws is, the Forgotten Realms has that opportunity. It's easier to immerse yourself in the world in that way than it is to decide "my character doesn't know this" or have to ask (which pulls you out of the immersion). It's much easier for me to modify things to my liking, which also keeps the players and the characters guessing. Because it's one thing for the character to "have" a feeling or know something, but it's a different thing altogether when the player does too.

A good example would be Ravenloft. It's fine to say your character is feeling a sense of dread, but it's much more fun if you can make the players feel a sense of dread too.