I read an interesting blog post last week about how "old-school" games are nearly always dependent on GM Fiat over Player Agency.
If I could find the post, I'd link back to it here. But the Goblins who deliver my internet have chosen to hide it from me.
It's an interesting topic, and one that crops up periodically. And, obviously, one that has led to a great deal of debate on the internet, because we're gamers and we'll argue about nearly anything.
But it led me to look back at some of the games I've loved over the years. And some of the players I've gamed with. Because discussing any aspect of theory in gaming can be very interesting, when all parties involved can keep a cool head - which is all too uncommon on the internet.
So first, let me explain what the two things are. From my perspective, because there's been a lot of discussion just about that. And it's not exactly new discussion, either. See, for example, this thread from eight years ago.
A game which relies on GM Fiat is one in which the GM has to make more decisions. Sometimes, this takes the form of a rules-light system without any sort of story points for players. Sometimes, this takes the form of a crunchier system. Either way, in a GM Fiat game, players control only what their characters do in the game. They have no direct control over the story or the greater world in which it is set outside of what their characters do to bring that change.
A game which relies more on Player Agency gives players more control over the broader narrative. In FATE, for example, players can spend Fate Points to take a small amount of control over the situation by triggering other peoples' Aspects (including those which are connected to a location or to an NPC). OctaNe allows players who make successful rolls to take complete (or near-complete) control of the narrative. Note that players with very strong player agency allow players to control even things their characters can't even influence. In FATE, I'd argue that the players are the ones with the Fate Points. Because a character can't realistically tag an opponent's Aspect. Or a place's aspect. It takes a player to spend that point to slow down an opponent who is trying to run away in the mud.
Realistically, most games have aspects of both GM Fiat and Player Agency. And there are good arguments to be made in favor of either playstyle.
Lately, I've been reading a ton of King Arthur Pendragon, Legend of the Five Rings, and 13th Age. All of these are mostly games with a strong GM Fiat element to them. In fact, there are several points in King Arthur Pendragon where the rulebook says, essentially, "the GM should decide." Determining player wealth during the Winter Phase, for example.
Neither aspect makes a game good or bad in and of itself. Many excellent games have allowed a great deal of player agency. And many excellent games have been almost purely ruled by GM Fiat.
13th Age is an excellent example. It is being hailed by classic gamers and storygamers alike as an excellent game - and with good reason, because it is an excellent game. But the rules (quite deliberately) don't cover every situation. For example: falling damage. If you fall off of a tall thing, the damage you take is up to GM Fiat. There are some guidelines on page 185 and a chart on 186 - but it's considered "impromptu damage."
Storygamers love it because of the worldbuilding they can do at character generation. For example, when I created Hochnor Half-Hand, I knew some of what I wanted to build into the world. By picking a Background of "Imperial Inquisitor," I decided for my GM that there was, in fact, an Imperial Inquisition. But once play actually starts, it's nearly all GM Fiat aside from the Icon Relationship Rolls, which players can theoretically use to steer the story at pivotal moments.
In theory, I prefer games with a degree of Player Agency. Not necessarily as strongly player-driven as OctaNe, mind you, but something. But, looking at games I've loved, I find that even as a player, I lean towards games with a strong GM Fiat.
My top five favorites:
Over the Edge
Legend of the Five Rings
OTE is much like 13th Age - player agency mostly ends after character generation.
Legend of the Five Rings gives a small amount of player agency with its void points and the ability of players to Raise on their rolls.
Paranoia is almost 100% GM Fiat.
Ars Magica allows players to design new spells and do so on the fly, but other than that, it's mostly driven by GM Fiat.