Lots of systems have a “rule zero.” It’s the rule that it only becomes apparent is necessary later, so it has to be added back in. But it’s also such an important rule that you can’t just add it on at the end: it informs all the later rules by its presence, answering questions and cutting through contradictions.
The Mayan zero symbol, via Wikimedia Commons.
Thermodynamics
In 1824, Sadi Carnot proposed the first (now numbered second) law of thermodynamics in Reflections On the Motive Power of Fire. By 1912, Nernst had formalized the last (now numbered third) law. But then, in the 1930s, Fowler realized something: these three laws all defined temperature in relation to entropy, and entropy in relation to temperature. Everyone kind of knew how temperature worked already. Many statements similar to the zeroth law already existed, but without first stating that “there is only one kind of temperature,” none of the other laws would be sufficient by themselves.
Euclid’s Elements
Euclid set forward 23 postulates and from them derived the rest of his geometry. Later critics have found many instances of proofs that require some additional postulate that was assumed in a later proof, but nothing to make the postulates themselves “invalid.” Euclid didn’t miss.
The United States Bill of Rights
As a compromise to ratify the U.S. constitution, James Madison added a bunch of amendments to ensure various specific enumerated personal freedoms and rights. But then the ninth amendment just says “oh yeah, and some other stuff.” James Madison fucked up! If that’s gonna mean anything, you’ve got to put it first, and then it colors the later amendments!1 And if you want it to sort to the top of the list, you’ve got to give it the smallest number: zero. It should be the zeroth amendment.
Dungeons & Dragons
D&D inherited a dictum from its wargame predecessors (who in turn inherited it from the free Kreigsspiel tradition) that the GM can alter or override any other rule at their discretion. As with the zeroth law of thermodynamics, it was often repeated, but not formalized as a rule until some time in the 70s. It’s unclear when exactly it became numbered “zero,” but the reason for doing so is obvious: by its meta nature it supersedes all later rules.
Magic: the Gathering
There are many ways to play M:tG, usually codified into “formats.” Formats can be sanctioned or unofficial, competitive or casual, rotating or static, global or local, dead or alive, and more. But one particular format has mostly eaten the whole casual scene: Commander (né “Elder Dragon Highlander”), which came neatly packaged with its own guiding principles, including a Rule Zero: that any rule can be malleable if the players all discuss it before the game starts. As with D&D’s rule zero, the overriding nature of the rule necessitates its placement at the start of the rules.
This has led to some confusion in spaces where M:tG players first come into contact with D&D, and presumably also vice versa.
I mean in a strictly psychological sense here, IANAL. I also know that Madison wanted the bill of rights to be incorporated into the body text, etc.↩︎