You know what, fine. Let me dust off that 3.5 PHB I buried.
Let us see here, pg 4 "The Core Mechanics: Whenever you attempt an action that has some chance of failure, you roll a twenty-sided die (d20). To determine if your character succeeds at a task (such as attacking a monster or using a skill), you do this:" It then lists out roll, add, check against DC and explains that meeting or beating the DC means you succeed and rolling below it means failing.
Maybe in this part on pg 5, What Characters Can Do "A character can try to do anything you can imagine, just as long as it fits the scene the DM describes. Depending on the situation your character might want to listen at a door, search an area, bargain with a shopkeeper, talk to an ally, jump across a pit, move, use an item, or attack an opponent. Characters accomplish tasks by making skill checks, ability checks, or attack rolls, using the core mechanic" This must be the rule you are looking for right? After all, it says character accomplish tasks and then give a list... though the first quote also says you only roll when there is a chance of failure. Hmm. I'll keep digging around.
The Player's Role? "As a player, you use this handbook to create and run a character. Your character is an adventurer, part of a team that regularly delves into dungeons and battles monsters. Play where everyone feels comfortable and there's a place to set ....[List of potential supplies]... and character sheets. The DM sets each scene and describes the action. It's your job to decide what your character is like, how he or she relates to the other adventurers, and act accordingly. You can play as... [another list, they loved listing different archetypes in this book]... With your character in mind, respond to each situation as it comes up. Sometimes combat is called for, but other situations might be solved through magic, negotiation, or judicious skill use."
Is this the rule that says players shouldn't use out of character knowledge in 3.5? It sounds like it, after all it is calling for players to play with their character in mind, to keep their character in mind when reacting. Of course, in 5e, there is an entire section of the book dedicated to player's backstories and personalities. So, while the rules never directly state you should keep your character in mind while responding to situations... it seems kind of heavily implied doesn't it? Your background and personality get their own chapter in 5e, while 3.5 they get a single paragraph each, with multiple pages written about the gods of greyhawk and the alignment system.
But, this isn't about personality, this is about using out-of-character knowledge. I doubt I'll find it in the races or classes section, so let us skip to skills. Surely if it is anywhere, it will be there right?
Well, what do you know, a whole sidebar about it. "It's pretty simple to measure a character's knowledge of things the player doesn't know. That's what a Knowledge skill check represents-for instance, the player of a character with many ranks in Knowledge (geography) isn't required to memorize all the geographical data about the campaign world to use his character's skill ranks. The opposite case, however, is harder to adjudicate cleanly. What happens when a player knows something that his or her character does not have any reason to know? For instance, while most veteran players know the black dragon breathes acid, it's entirely likely that most inexperienced characters don't know that fact. Generally speaking, it's impossible to separate completely your personal knowledge (also called player knowledge) from your character's knowledge. Ultimately, the decision on how (or if) to divide player knowledge from character knowledge must be made between the players and the DM. Some DMs encourage knowledgeable players to use their experience to help their character's succeed. Other prefer that characters display only the knowledge represented by their skill ranks and other game statistics. Most fall somewhere between those two extremes. If in doubt, ask your DM how he or she prefers to handle such situations. The Dungeon Master's Guide has more information on this topic."
So, I guess that is the final verdict. I was corrupted by the sidebar in the 3.5 PHB that said that is was up to the DM whether or not players should use out of character knowledge. Wait, no, I was probably lured in by homebrew table cultures of people in my area to think that using out of character knowledge was discouraged.
I mean, 3.5 said either way is fine, and 5e doesn't even talk about it at all except in that section where they talk to DMs about how they might want to handle this exact issue. The rules in these two games are just so entirely different, I'm shocked I got them so mixed up.
