Nomic actually refers to a large number of games based on the initial ruleset laid out by Peter Suber in his book The Paradox of Self-Amendment (The ruleset was actually first published in Douglas Hofstadter's column Metamagical Themas in Scientific American in June 1982. The column discussed Suber's upcoming book, which was not actually published until years later.) The game is in some ways modeled on modern government systems, and demonstrates that any rule-changing system can get into a situation in which the laws are contradictory or insufficient to determine what is legal. Because the game models (and exposes conceptual questions about) a legal system and the problems of legal interpretation, it is named after νόμος (nomos), Greek for "law". (See also nomos.)
While the victory condition in Suber's initial ruleset is the accumulation of 100 points by the roll of a die, he once said that "this rule is deliberately boring so that players will quickly amend it to please themselves." Players can change the rules to such a degree that points can become irrelevant in favor of a true currency, or make victory an unimportant concern. Any rule in the game, including the rules specifying the criteria for winning and even the rule that rules must be obeyed, can be changed. Any loophole in the ruleset, however, may allow the first player to discover it the chance to pull a "scam" and modify the rules to win the game. Complicating this process is the fact that Suber's initial ruleset allows for the appointment of judges to preside over issues of rule interpretation.
Initially, gameplay occurs in clockwise order, with each player taking a turn. In that turn, they propose a change in rules that all the other players vote on, and then roll a die to determine the number of points they add to their score. If this rule change is passed, it comes into effect at the end of their round. Any rule can be changed with varying degrees of difficulty, including the core rules of the game itself. As such, the gameplay may quickly change.
Rules are divided up into two types: mutable and immutable. The main difference between these is that immutable rules must be changed into mutable rules (called transmuting) before they can be modified or removed. Immutable rules also take precedence over mutable ones. A rule change may be:
Alternative starting rulesets exist for Internet and mail games, wherein gameplay occurs in alphabetical order by surname, and points added to the score are based on the success of a proposed rule change rather than random dice rolls.
Online versions often have initial rulesets where play is not turn-based; typically, players in such games may propose rule changes at any time, rather than having to wait for their turn.
One spin-off of a now-defunct Nomic (Nomic World) is the Fantasy Rules Committee, which adds every legal rule submitted by a player to the ruleset until no more rules are possible. Then, all the "fantasy rules" are repealed and the game begins again.
The fictional game Calvinball, played by the main characters in the comic strip Calvin and Hobbes, is sometimes compared to Nomic. However, Calvinball appears to have a permanent rule that the same rules may never be used twice; a nomic, at least in its initial state, has no truly permanent rules.
Another facet of Nomic is the way in which the implementation of the rules affects the way the game of Nomic itself works. ThermoNomic, for example, has a ruleset in which rule changes are carefully considered before implementation, and rules are rarely introduced which provide loopholes for the players to exploit. B Nomic, by contrast, was once described by one of its players as "the equivalent of throwing logical hand grenades."
This is essentially part of the differentiation between "procedural" games, where the aim (acknowledged or otherwise) is to tie the entire ruleset into a paradoxical condition on your turn (a player who has no legal move available wins), and "substantive" games, which try to avoid paradox and reward winning by achieving certain goals, such as attaining a given number of points.
While Nomic is traditionally capitalized as the proper name of the game it describes, it has also sometimes been used in a more informal way as a lowercased generic term, nomic, referring to anything with Nomic-like characteristics, including games where the rules may be changed during play as well as non-gaming situations where it can be alleged that "rules lawyers" are tinkering with the process used to amend rules and policies (in an organization or community) in a manner akin to a game of Nomic.
The Nomic Wiki at nomic.net contains a list of active online Nomics