“Rules, not Rulings” and “Rulings, not Rules” are supposedly the primary distinction between Old-School and New-School play.
I designed the “old-school” edition of Materia Mundi (now tenatively called ‘BXN’ in an act of supreme marketing hubris) to support Old-School play with a lightweight grab-bag of new-fangled tools.
N-in-6 Skills, and “Average Competency”
The original B/X “N-in-6” task checks are an excellent example of old-school mechanics. They are blindingly fast to execute, intuitively easy calibrate, and quick to communicate.
Lamentations of the Flame Princess was my first exposure to whole skill systems built around the N-in-6 concept; I liked it enough to mutate it horribly and bolt it onto my 4E/5E hybrid tactical game (the one that eventually mutated further, pupated, and emerged from its cocoon as Materia Mundi/BXN).
The thing that makes N-in-6 so easy to work with, is that there’s only seven possible statistically distinguishable outcomes:
impossible
really unlikely
kinda unlikely
even chance
kinda likely
really likely
sure thing
This makes it really easy to chunk things into human-comprehensible probabilities. Turning this into a skill system also makes it easy to calibrate where the “midpoint” is. This midpoint is the natural place to put your ‘rules pivot’ — that is, the default assumption that you can then start branching exceptions off of.
So, we have two core numerical assumptions that need to combine, to determine the difficulty (statistical likelihood of success) of the task:
Skill level - how competent the character is at the task
Challenge level - how difficult the task would be for someone of standard competence.
Skill level is a number on the player’s character sheet.
Challenge level is a number that the referee needs to come up with.
The rules need to input these two numbers, and output what dice to roll and how to interpret the numbers that come up on them.
Proficiency, Expertise, and Ineptitude
There are a lot of terms for “skill level”. D&D seems to have settled on the term “proficiency”, but that term is sufficiently overloaded that it didn’t feel useful to import into BXN. Instead, we simply have a “target threshold”. This starts at 6+, unless you have a relevant ability score that is exceptional or deficient — in which case it might start at 5+, or at inept (7+, aka don’t-bother-rolling).
Then, each level, you can improve one or two of your skills (depending on your character class) by one point each, where “improve” means lowering the threshold by 1, down to a minimum threshold of 2+. So an average character that has no particular talent, but is investing fully into a particular skill, can reach 4+ at level 3 — and 4+ is a 50/50 even chance of success.
This is an excellent pivot point to balance the rules around — an average level 3 character has standard competence at the skills in their wheelhouse.
Normal, Easy, and Hard
So, a task of “normal difficulty” is any task that a character with 3 levels worth of experience should be able to perform successfully half the time, assuming that task is part of their schtick.
Which means that a task of “easy difficulty” is any task that a character with 3 levels of experience should be able to accomplish noticeably more often than not, but still with some amount of risk, assuming that task is part of their schtick.
And a task of “hard difficulty” is anything that that character should be able to accomplish sometimes, but noticeably less than half the time, assuming that the task is part of their schtick.
Materia Mundi/BXN is built around the philosophy that you really don’t need any higher-resolution probabilities than this. Anything sufficiently harder than “hard” is effectively impossible; don’t bother rolling. Anything sufficiently easier than “easy” is effectively automatic; don’t bother rolling. If there’s any meaningful chance at all of succeeding, give them a roll at “hard” difficulty. If there’s any meaningful chance at all of failing, give them a roll at “easy'“ difficulty. In most situations, just let them roll at normal difficulty.
And mechanically, “easy” just means “roll 2 dice and take the better one”; “hard” just means “roll 2 dice and take the worse one”. BXN operates on the hypothesis that this is sufficient for pretty much any situation you’ll need to handle.
Comparison with 5E
Note that this situation is pretty much the inverse of 5E’s skill system — BXN gives you 6 steps of skill “proficiency”, but only three steps of “difficulty”; 5E gives you three steps of skill “proficiency” (untrained/proficient/expertise), and a fine-grained dial for “difficulty” (since difficulty is always a D20 target number).
I assert that this is exactly backwards.
The referee and player shouldn’t spend a whole bunch of time working out little bonuses and penalties to settle on a number to roll. The “number to roll” should be right on your character sheet, determined by your class level and abilities. When you go up a level, you should always see these numbers getting better.
Then, when you’re in the thick of it, figuring out the core question — “based on how the player is describing their character’s actions, is this impossible, hard, normal, easy, or automatic” should be a snap-fast decision for the referee.
This, I argue, is the essence of what “rulings, not rules” is trying to capture.
Players Describe Actions
An action should start with a player’s description of what they’re trying to do. No numbers on the player’s character sheet should be referenced at this step. This is what “Play the world, not the game” means. The referee describes what the player characters experience through their senses, and then the players describe what actions their characters are performing — not what action-procedure-rules the player is invoking.
Referees Describe Consequences
The referee then decides what action-procedure-rules are invoked by the player’s action, and performs those procedures — inviting the player along where appropriate. Dice get rolled, the referee uses their intuition and the rules-as-written to digest the result of those dice, and then the referee describes what unfolds as a result of the player’s actions — again, through the player characters’ senses.
Keeping the range of difficulty levels “thick” and “chunky” helps lower the cognitive overhead that the referee needs to process, in order to perform that duty.
