okay maybe we can try this again... just read what I write and not try to read some evil DM trickery into it please...
I mean I find it exactly as enforceable as every other part of our hobby... if 1 player keeps doing it then it will make the game less fun for the rest of us... over time we will talk this out, and if we can't find someway to make it work we will split ways...
what do you mean be enforceable?
I realize now I need to give you very concrete examples.
For the last 3 years my group has only been meeting remotely over Discord. Now, supposing I was the sort of GM that got upset with players using their player knowledge to inform how they played the character. And suppose I then announced a table rule, "Don't read setting books and scenario books at "the table". Don't open up rule books in response to things that happen in the game." How would I be able to know when the table rule I just announced was being broken given that I can't see what pdfs or books the players have open? And what would I do about it if it was?
So no, my table rule isn't then exactly as enforceable as anything else.
On the other hand, if I had a table rule that said, "Just because you announce the intention to attack first, it doesn't mean that you get any advantage on surprise or initiative. In order for one character to surprise another, the character must not be aware of the other. However, I will allow the following exception. If you achieve a friendly relationship with a target, if your Disguise check beats their Sense Motive check, I will allow surprise because they weren't expecting an attack because they saw you as a friend. Keep in mind this doesn't work if the target is only pretending to be friendly. If the situation is an NPC trying to attack a PC, I hold the last word on whether your character honestly believed the NPC to be a friend, but you can still roll to avoid surprise."
Isn't it then obvious, how I as the GM would enforce that as a table rule? Isn't it obvious I have enough authority over the game as the GM to enforce a table rule like that?
okay when I think metagaming I think using out of character knowledge for ingame benefit
That's pretty close to my definition, though I'd make yours even more simple. I think of it as using out of character knowledge period, and why you do it doesn't really matter. Yes, most often players are using their out of character knowledge for in game benefit, but I don't think the motive matters as much as the action. Because again, neither of us are mind readers and to a large extent what your intention is doesn't matter as much as the result. And I think you kind of get this because you say:
"(in theory there is a form where I guess you takeout of game knowledge to use in game to no benefit too)"
I doubt anyone can ever make such things impossible... but again I am just thinking at the tables I play at we try to minimize it...
So here is my point. Once the player has out of game knowledge that impacts the in game, it's too late to minimize it. That knowledge is out there and no matter what the player does, he'll be metagaming. So the only functional way to minimize metagaming is to minimize the leakage of out of game knowledge to the player. And the only important knowledge to minimize that is within the GM's purview.
So we have the same goal. I'm using secret rolls when needed, and DM screens, and so forth in order to prevent having a situation where the player's game is ruined by his own out of game knowledge. Where as you are doing everything out in the open and then blaming the player for receiving the information you provided them. My way seems more functional and well more fun.
Moreover, everything in this thread is actually about a process of play that keeps my game in character more often than yours. That's my motive. Which is why when you describe processes of play that make the game more out of character and insist it's keeping it more in character, it is baffling.
we don't see it as fun if we play with full out of game knowledge.
Yes, but it's impossible to play without your full out of game knowledge. You can't erase what you know from your own head, and in the general case that knowledge is always informing your choices even when you are trying to not let it inform your choices. So you aren't actually offering solutions to the problem as I see it, where as I am offering solutions to the problem as I see it.
I have not used a screen since I started playing 4e, and right now we are using roll20... we don't hide things out of game because we trust each other not to use it in game.
It has nothing to do as trust. I know from my experience as a player that it's impossible to ignore what you know as a player. You can't not use what you know except by non-participation, which is itself metagaming.
I can't imagine how much less fun I would have as both a player and a DM if I had to constantly worry about if I did something out of game.
And I could say the same thing back to you. Because it's only at your table that the players have to worry about whether or not they are metagaming wrong. I've explained this to the players before. "Metagame to your hearts content. Just beware. I've got a 150ish IQ and 40 years of experience, so don't assume that you can just jump to conclusions about something. I won't metagame against you and change prepared text or invent counters on the fly, but the knowledge you get in game is always more reliable than your out of game assumptions"
I don't think it's 'on you' or 'on them'
I can make mistakes as a GM. If in an OOC comment I the GM accidently blurt out the real name of the BBEG rather than his assumed identity, and thereby give the players the key to the mystery, well that's not my players fault and I can't expect them not to act on the new found knowledge. I won't demand they even try pretend they don't know the very information I just gave them and that it doesn't now inform their actions.
So, back to the concrete example. Suppose you are GM Alien RPG and the players are colonial marines exploring a jungle world as part of biological survey mission. And something happens in game that is pretty innocuous, like the players find one of the NPC has been beheaded in the jungle, but causes a player to think and this happens:
PC #1: "Wait a minute guys. I bet we aren't actually fighting Xenomorphs this time. I bet this scenario we are fighting a Predator"
PC #2: "Oh heck no, I bet you are right. We need to start laying traps, using the environment, and trying to see if we can penetrate the Predator's stealth suit. And let's start watching each others back for those red dots."
What do you do as a GM? For me, this changes nothing. The players are engaging with the scenario. What do you do?
Is it any different than,
PC #2: Geez, this guy was beheaded. And I can't find the head anywhere.
PC #1: When we get back to camp, Sgt Walls starts putting up traps and perimeter defenses around the camp. I also want to get some motion detectors and set them up around the perimeter of the camp and order everyone to start digging a bunker, that no one can be out of sight of the others, and tell them we can't sleep in the tents tonight.
Because for me it isn't different. I don't worry about or care if in his head he's figured out it's a Predator and he's using his OOC knowledge about Predators.