While I explore this site, I occasionally see the phrase "GM fiat" (or "DM fiat", for D&D questions and answers), but I don't know the exact meaning of that. I want to know the meaning of that terminology.


In a large number of RPGs the GM is positioned as the controller of the world, its NPC inhabitants, the items in the world, and their essential natures. They are also often positioned as the final arbiter of rules and thus hold considerable authority. It tends to be these games in which “GM fiat” is a thing. Hopefully a GM imbued with such power will remember: with great power comes great responsibility.

With that said, a fiat is defined as:

  1. an authoritative decree, sanction, or order
  2. (irrelevant)
  3. an arbitrary decree or pronouncement, especially by a person or group of persons having absolute authority to enforce it

So a GM fiat is when the GM says something is the case — because they have the authority to do that — and it becomes the case.

A GM fiat is produced independently by the GM. It is separate to decisions made by the group as a whole: a GM can declare a house rule as a GM fiat, but that's different to the group producing a house rule together.

Implicitly the GM is not required to justify or explain their fiat — these things just happen because you're the GM and get to make them happen.

Because GM fiats are arbitrary and can involve major changes (like the changing of the rules themselves) the motto of “with great power comes great responsibility” is massively relevant. These changes could make the game more fun or extremely un-fun for players.

Some examples of usage of GM fiat

  • Create your own fluff for in-game races, civilisations, etc, which may either add to or replace lore from the books.
  • Create new material in the universe, such as:
    • New items which don't exist in the game's rulebooks.
    • New planes, gods, and so on. A fellow member of this site once played in a game where all bags of holding lead to their own demiplane, with a Demigod assigned to guard all such demiplanes.
    • In D&D, create a Freezing Hands spell as a cold equivalent of the actually-in-the-books Burning Hands, and give it to one of your players or NPCs.
  • Make a declaration about how a certain rule works, especially for clearing up ambiguities.
  • Make rulings where there is no clear rule.
  • Declare that something simply happens when there is no clear justification for it.
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Fiat comes to English from the Latin Fiat, which is the third-person active subjunctive of Fierī (to do), basically meaning "Let it be done".

It is used in English usually to mean a decree or judgement, so a "GM Fiat" is essentially a way of saying "The GM says this is the way it is, so this is the way it is, no arguments."

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Fiat: by decree.

In the context of gaming, GM Fiat means, literally, "because the GM says so."

Anything more is context dependent.

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Fiat in Latin means "let it be" or "let it be done". It roughly means to make a decree.

DM/GM Fiat in particular is generally considered the act of a GM arbitrating things not covered by the rules, declaring house rules or creating a rules clarification that does not exist in the pre-written material.

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DM Fiat often goes along with what is also known as Rule Zero: The DM's judgement is final and supercedes all other officially documented rules. Essentially, they have the ultimate authority, and can make any decision they wish without being able to be overruled. As with any such dictator-like power, this can be used for either good or ill, but has become most famous for the worst of examples, such as with DMs making abusive or simply foolish decisions.

This rule can be considered inaccurate, however, and an additional term has come to represent this fact: Rule Negative One: What the gaming group as a whole agrees upon is final and supercedes even Rule Zero, because if everyone is unhappy, then they will leave and there simply is no game. It's useful to remember that a DM can not truly bully the players, because it is just a game, and everyone can just opt to not play with them; perhaps go play a new game with a new DM that doesn't make such abusive fiat decisions.

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  • 6
    \$\begingroup\$ I am not sure it's actually helpful to talk about Rule Zero, because that concept only exists in a handful of RPGs (and within the D&D community). In other games where something like it exists, it is often a different concept or goes by a different name. Rule Zero itself is far from universal. (I don't wish to upvote because I don't even really want to acknowledge these two 'rules') \$\endgroup\$ – doppelgreener Jan 22 '14 at 15:07

It means that the GM is the one in charge of the game and what they say goes, even if it blatantly contradicts whatever rule books say.

It in essence means that their authority over the game is absolute and something can be the way it is just because they said so and no other reason.

Relatedly however, there are two caveats:

Knowing the rules

The rules exist for a reason and their existence implies an expectation of consistency, and rightly so, on the part of the player.

A good GM should know the rules very well so that he knows whether or not he's going by the book or pulling something out of his proverbial ass as it ere.

Not being a jerk

The authority of a GM is not bestowed as a toy. Its purpose is to uphold the order of the group and give the GM the creative freedom he needs to tell his story.

It is the responsibility of a GM not to abuse his power or use them to be a jerk, because that itself undermines the social contract he made with the players that let them collaborate on the game in the first place.

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  • \$\begingroup\$ I'm not sure that your first caveat necessarily applies. Depending on the system and your group's expectations, GM fiat may be used to override the rules where the rules' results seem inappropriate, rather than simply to fill gaps which the rules don't cover. (e.g., "I have the BBEG tied to a chair, so I slit his throat". In some groups, the GM would declare the BBEG dead by fiat instead of following the normal damage rules and making the PC stab the BBEG 57 times to chew through all of his HP before he can be killed.) \$\endgroup\$ – Dave Sherohman Mar 26 '19 at 9:56

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