It's funny, how much attentions some old-school games pay to something like accurate accounting of supplies for dungeon expeditions (how many torches, how many rations, how much they weigh, etc. with tremendous meticulousness), and yet how little attention they give to social factors of the world; to thinks like the differences in expectations and behaviours in the social classes, or how to behave in front of nobility. I've found it super-common, in other people's groups, that there's a total disregard for this sort of thing, that it's treated like a really bad American Movie about the "Olden Days" where everyone is still fundamentally acting like 21st century people, where you have the peasant guy wise-cracking in front of the knight at his expense or the scullery maid bad mouthing the duke and being respected as a heroine, rather than being sent off to be brutally beaten.
And this becomes a case of contention with new players to my groups; because my fantasy games are very rarely like the above (unless it's something completely Gonzo, like my current DCC group). We had more than one fresh-faced brand-new player of Albion that didn't realize that being in the Earl's court was possibly more tricky terrain than being in a catacomb, and who thought they should just get to chime in with their opinion whenever. The most egregious cases thinking they could tell their social betters off, sure, but even the relatively smarter newbie-players never at all hesitating to think that at a meeting where they were allowed to be present they should of course get to give their opinion unbidden!
(and no, I didn't punish the players for what they didn't understand; not the first time. The guys who still didn't get it after repeated occasions and wanted to keep acting like hip 21st century rebels standing up to 'the man' ended up getting their natural comeuppance)
Now, it's to be expected that given this total disregard for proper etiquette in most games (and noting that D&D is fundamentally an American game, and Americans don't even begin to understand etiquette anymore, and they were pretty shaky on it from the start), we don't get much help from either rules or more setting books. At best, we get some kind of 'etiquette' skill, that treats the understanding of what to say or how to act in front of your social superiors, equals or inferiors as some kind of "knowledge" skill. On its face, that might seem a good choice (probably, an "obvious" choice to a North American that really doesn't know better, for lack of a class system), but it isn't.
There shouldn't be an "etiquette" skill (or if there were, it shouldn't be what you roll for how to act in a social situation). The real answer is that "etiquette" should be determined by Social Class, and what there needs to be is some kind of social class indicator (not necessarily a mechanic in the sense of a 'number', but something that tells you what your PC is), and on anything that isn't being role-played (and note: as an old-schooler I really think most things SHOULD be role-played), that social class indicator should be what governs how things go down.
It's still a little bit true even in our society to this day, that 'etiquette' is not something you consciously learn (or in those rare cases where you try, you will at best do it BADLY); instead it's what they used to call "breeding". It's actually a whole set of instruction-by-osmosis from childhood that a person has based on the social class they are born into, which are different if you're born into the working poor, the bourgeoisie, or the aristocracy. This means that any situation where an 'etiquette skill' would need to be rolled (as in, to see if the PC knows or doesn't know how to behave) would be one where the PC has already failed, and will, AT BEST, do it less badly than someone who understands where they belong from the start in that situation.
So in most cases, NO roll should be needed at all. If a character is from a certain background they will already know how to behave in a given situation; if they are not, they cannot know (but may know how to be appropriately deferential, as that's an inherent training people from the lower classes receive). Something like Charisma modifiers can determine how effectively they perform or if they are less or more attentive to social conventions and expectations.
But as for "knowing what to do"? The ONLY time I could see an etiquette "skill" being required would be if you were talking about someone who specifically had researched the subject in order to study it academically (someone working in some finishing school or that sort of thing; or a scholar from one culture who had studied the proper manners of another culture for anthropological or diplomatic purposes) or if you had some rogue who had been training in order to know how to falsely impersonate a member of a different social class than their own (in which case, you might as well just use Disguise or Acting or whatever, because that's what it is).
People make the mistake of treating etiquette as a "do I know this" skill. This is probably because in our modern times it seems like no one knows any etiquette; in point of fact this is not true, its just that we associate "etiquette" with old-timey "manners" from the Victorian age. Etiquette isn't really about which spoon to use, that's the most superficial aspect, and it seems like a knowledge-thing (and at the same time so silly) because that's only the most superficial of the layers of it, and one our society has largely discarded. But we do, in fact, still have the same lower-layers, even if not to the same extent.
We have modern "etiquette" all the time, and that's what you have to envision 'etiquette' as if you want to understand it in a medieval context too. You see it whenever you have someone raised in a minimum-wage or welfare-dependent household having trouble fitting in visiting the family of their "slumming-it" upper middle class girlfriend/boyfriend (among countless other situations like those). The "fish out of water" syndrome happens because of differences in social class, where people have been taught in early childhood how you're EXPECTED to act within your class. That code of 'how you're expected to act' is etiquette, and it applies in all kinds of different situations; but your parents can't teach you about situations they don't know, and even in events common to all classes (family get-togethers, for example) the "rules" taught of how you're supposed to behave, what you're supposed to say, dress, how and when to eat, acceptable subjects of conversation, etc., are different from one class to another. Etiquette is often portrayed as a set of rules of 'good behaviour' but that's not what it really is at all! Etiquette is actually a code for how to act "like one of us", whoever 'us' is. Knowing to eat a chicken-drumstick with a knife-and-fork is proper etiquette at an upper-middle-class table, and knowing to eat a chicken with your hands is proper etiquette in a lower-class table, and being in breach of either of them produces the same result: you get identified as an outsider, as someone who doesn't belong or who is refusing to belong.
What I'm saying is that a PC raised in a noble household shouldn't need to "roll" anything to know how to act toward ladies at court; he's been taught that ALL HIS LIFE. The GM should instead just tell him what he knows about how he's expected to act, and then the player should decide whether they want to be scandalous by intentionally ignoring those rules or not. Its never ability, it's willingness.
(breaches of etiquette caused by accident or lack of care should be most unusual events. Also, the fact that hardly anyone today could look at this picture and actually understand what's going on is proof of what I'm talking about)
Likewise, unless someone has been specially trained/studying etiquette actively and on purpose, there shouldn't be any way they could possibly know how to act, because etiquette is MEANT to root out 'intruders' to social class. It's like sumptuary laws of the mind, rules taught to prevent impostors from climbing above themselves (though it also works the other way, rooting out 'fakers' from the higher classes trying to pass themselves off or hobnob undetected among the hoi-polloi). Obviously, if a peasant PC intentionally sets about getting training in how to act, then they may be able to attempt it, but otherwise, generally speaking, people are never taught the REAL secrets of etiquette. It's like the way people in the aspiring middle class used to think it was 'fancy' to raise the pinky finger while drinking tea, while actual upper classes would never ever do that and would immediately recognize it as a sign of ignorance. Or how when a gentleman asked you "how do you do", you never said "good" (much less "bad"), you always only reply "how do you do" right back, neither of you ever actually answering (unless you're dear dear friends). Just learning what spoon to use for what course is not going to save you; though that, too, was a set of brutal rules meant to distinguish commoners from aristocrats, natives from foreigners, the people who should be there (in other words) from those who have no place being there.
(one place where you can still see this is with Asian food. Most white people have no idea, even those who think they do, of all the little rules of behaviour that are going on in a sushi place or a Dim Sum restaurant, and they are used to distinguish the 'civilized' from the 'barbarian'. When I lived for some time in Vancouver's Chinatown, I had to learn enough of the secret etiquette of dining that I can now surprise most 'locals' at a Chinese restaurant, but even after all that time and learning it largely served to make it clear to me just how impossible it would be for me to ever really be an 'insider'; instead, all my study of etiquette for dining at a Dim Sum restaurant or what-have-you has, at best, made me an oddity, a curiosity, the "white guy who knows how to drink tea properly and doesn't eat like a total slob"; and short of spending decades inside this culture, that's the absolute best anyone could hope to do)
In a fantasy society (or any society up to about the mid-20th century) people could interact with higher or lower social classes; but NOT as one of them. Instead, lower class people were taught (also as etiquette) how they should behave, as lower class people, in front of their "betters"; and likewise, upper class people were taught the 'proper' way to behave around their 'inferiors'. Not to 'blend in', but to specifically highlight those differences. This too should never ever need to be "rolled for"; a peasant shouldn't ever have the risk of accidentally failing to show proper reverence to a Lord, because it has been unconsciously drilled into them by osmosis their entire lives. Again, unless they were willingly and willfully choosing to break those rules in an act of defiance.
Given all this, and on such an old-school subject, it comes down to roleplaying and not rolls. Etiquette and proper behaviour at court should be something explained by the GM, almost never needing to be rolled for, and where the GM must go to lengths to emphasize just what the PCs already know they need to do or how to act. And then, it is up to them if they choose to break those rules of behavior or not. But if they do engage in such an 'act of defiance', the GM may want to make clear to them that this is another case of the past being "another country" and that back then 'fighting tradition' was almost never something that anyone was going to look at with any kind of admiration.
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