#add 2e

“Rule 0” is an unofficial term for a fundamental aspect of tabletop role-playing games: the DM’s word is Law. Some games have no referee at all, but if there is such a thing as a Dungeon Master, Game Master, Storyteller, etc, then what they say goes.

This can mean two things. The first is “what they say goes, as opposed to what the players say”. Someone has to be the final arbiter on how rules are interpreted and what happens in game. And if the DM says Rocks Fall Everyone Dies, well, rocks do fall and everyone does die. (And whatever led to that should be addressed out of game.)

The second is “what they say goes, as opposed to what the rulebooks say”. As far as I know, no RPG designer has ever had the gall to claim that the rules are final and you shouldn’t change anything. Sometimes it’s left unsaid (and probably considered obvious), but most of the time rulebooks explicitly state that the DM (Game Master, Storyteller, etc) can change the rules. The attitude varies, ranging from “rules are a suggestion! do what you want!” to “you can make changes BUT take into account this and that”.

I find it interesting that D&D 3rd Edition is the most stringent in this regard. It doesn’t say “change the rules as you see fit”, it rather says “well if you must change the rules, do it right”. It makes sense, I guess: that edition was BIG on simulation, and having rules for every little thing. Like, you can calculate how many hit points the wall has, depending on size and material. That means the DM can tell how many punches it takes to break each specific wall, since unarmed attacks deal damage to objects (half dmg, but still). It also suggests that the DM shouldn’t say “you punched the wall? okay, your knuckles bleed, it hurts like hell, and the wall is fine”, which for some styles of play is in fact unfortunate, because that’s exactlywhat the DM should say.

(There’s no right or wrong here, different strokes for different folks, and every system caters to different needs.)

I also find it interesting that the very similar Pathfinder is conversely generous, and singles out Rule Zero as “The Most Important Rule”. This also makes sense, given that Pathfinder is essentially a house-rules project that got out of hand.

In any case, here’s a selection of different ways to say “the rules are a suggestion”.

Original D&D (1974)

“These rules […] remain flexible. As with any other set of miniatures rules they are guidelines to follow in designing your own fantastic-medieval campaign. They provide the framework around which you will build a game of simplicity or tremendous complexity — your time and imagination are about the only limiting factors.”
– Dungeons & Dragons Book I: Men & Magic

Basic D&D (aka Eric Holmes’s revision, 1977)

“Instructions for the game referee, the “Dungeon Master,” are kept to the minimum necessary to allow him to conduct basic games. This is absolutely necessary because the game is completely open-ended, is subject to modification, expansion, and interpretation according to the desires of the group participating, and is in general not bounded by the conventional limitations of other types of games.”
– Dungeons & Dragons Basic Set

AD&D (1979)

“The final word, then, is the game. Read how and why the system is as it is, follow the parameters, and then cut portions as needed to maintain excitement. […]  The game is the thing, and certain rules can be distorted or disregarded altogether in favor of play.”
– Dungeon Masters Guide

Basic D&D: B/X (aka Tom Modvay’s revision, 1981)

“In a sense, the D&D game has no rules, only rule suggestions. No rule is inviolate, particularly if a new or altered rule will encourage creativity and imagination. The important thing is to enjoy the adventure.”
– Dungeons & Dragons Basic Rulebook

Basic D&D: BECMI (aka Frank Mentzer’s revision, 1983)

“You may use all or part of these rules. They often include several ways of playing and running the game. You may create new rules, monsters, and magic, using these rules as guidelines.”
– Dungeons & Dragons Fantasy Roleplaying Game Set 1: Basic Rules

AD&D (2nd Edition, 1989)

“Take the time to have fun with the AD&D rules. Add, create, expand, and extrapolate. Don’t just let the game sit there, and don’t become a rules lawyer worrying about each piddly little detail. If you can’t figure out the answer, MAKE IT UP! And whatever you do, don’t fall into the trap of believing these rules are complete. They are not. You cannot sit back and let the rule book do everything for you. Take the time and effort to become not just a good DM, but a brilliant one.”
– Dungeon Master Guide

D&D (3rd Edition, aka 3.0, 2000)

“Changing The Rules: Beyond simply adjudicating, sometimes you are going to want to change things. That’s okay. However, changing the rules is a challenge for a DM with only a little experience.”
– Dungeon Master’s Guide

Note: I won’t quote the whole thing, but it goes into some length on what to consider before changing a rule. I’m gonna bet that when they suggested you ask yourself “How will the change impact other rules or situations” they hadn’t predicted that 3rd Edition would end up with 215 books full of interconnected rules, NOT including adventures and periodicals.

D&D (Version 3.5, 2003)

“The power of creating worlds, controlling deities and dragons, and leading entire nations is in your hands. You are the master of the game—the rules, the setting, the action, and ultimately, the fun. This is a great deal of power, and you must use it wisely.”
– Dungeon Master’s Guide

Note: I won’t quote the whole thing, but it says there are different styles of play, and if you like combat-oriented games you should be “very careful about adjudicating rules and think long and hard about additions or changes to the rules before making them”, whereas if you’re into deep-immersion storytelling, rules become less important: “feel free to change rules to fit the player’s roleplaying needs. You may even want to streamline the combat system so that it takes less time away from the story.” Or you can go for something in between.

Deadlands (Revised Edition, 2004)

“The rules in the Weird West Player’s Book are fairly detailed. […] Characters need all that detail because they can’t cheat. But you’re the Marshal. You can do whatever the Hell you want to, and that’s official partner.”
–The Marshal’s Handbook

GURPS ( Revised Third Edition, 2004)

“The GM is the final authority. Rules are guidelines … the designer’s opinion about how things ought to go. But (as long as he is fair and consistent) the GM can change anynumber,anycost,anyrules.”
– GURPS Basic Set

D&D (4th Edition, 2008)

“If you disagree with how the rules handle something, changing them is within your rights.”
– Dungeon Master’s Guide

Pathfinder (1st Edition, 2009)

“The Most Important Rule: The rules in this book are here to help you breathe life into your characters and the world they explore. While they are designed to make your game easy and exciting, you might find that some of them do not suit the style of play that your gaming group enjoys. Remember that these rules are yours. You can change them to fit your needs.”
– Pathfinder Roleplaying Game Core Rulebook

D&D (5th Edition, 2014)

“The D&D rules help you and the other players have a good time, but the rules aren’t in charge. You’re the DM, and you are in charge of the game.”
–Dungeon Master’s Guide

Vampire: The Masquerade (5th Edition, 2018)

“If the rules in this book interfere with your enjoyment of the game, change them.”
–Vampire: The Masquerade (5V corebook)

Legend of the Five Rings (5th edition, 2018)

“Your Game, Your Rokugan: This game is designed to support numerous styles of play and, as GM, you are empowered to jettison, rework, or simplify rules as you desire.”
– Legend of the Five Rings Core Rulebook

Pathfinder (2nd Edition, 2019)

“As Game Master, you have the final say on how the world and rules function.”
– Pathfinder Core Rulebook