A game I play in spawned some rambling confusion about GNS- what it is, what it means, and how it's supposed to be used. GNS are probably the three most often misused term in the Forgist glossary, so this doesn't particularly surprise me. This is my no-nonsense attempt to explain GNS, while using as few Forge words as possible to ease acessibility.
(Ron Edward's intro to GNS is
here, but I didn't really understand it until I read it, misunderstood other stuff, and then came back six months later and read it again.)
So, what is GNS? GNS stands for Gamism, Narrativism and Simulationism. That's great, but what are G, N, and S? The idea is that they are three modes of describing what actually happens when people sit down and roleplay.
Note that GNS describes PLAY, not PEOPLE, and not GAMES. People will often say things like "I'm a Gamist" or "Dogs in the Vinyard is too Narrativist for my taste." Those people are using the terms incorrectly. Most of those people even know better, and are too lazy to say things like "I tend to prefer Gamist play sessions," or "Dogs in the Vinyard tends to create Narrativistic play." (With good reason: those sentences can be mouthfulls. But this increases confusion about what GNS actually means. So shame on them.)
SIMULATIONIST play is what people tend to be most familiar with. It focuses on 'simulating' some aspect of gameplay: often, one's character. Gameplay is focused on figuring out what the deal is with one's character, and expressing that. Essentially, the player's are playing SimFighter or SimWizard, but character isn't the only thing Simulationism can focus on. Sometimes, exploring the world the GM has designed (or has bought the sourcebooks for) is what everybody cares most about, and everyone wants to know what sort of crazy stuff is in the next town. (These subsets are called focuses of Exploration, but you don't need to know that.)
Rules that are designed to facilitate play often put the focus of design on 'realism' or 'genre emulation,' or have options that allow a player to more clearly define their character in rules terms to facilitate showing other people the awesome character they've come up with.
The literary equivalent of simulationist play is a biography or gazeteer; such books seek to describe something in depth.
NARRATIVIST play focuses on telling a compelling story. This sort of play has a plot with twists and turns and dramatic highs and lows. When it's good, everyone is on the edge of their seats wondering and plotting just what's going to happen next. Because storytelling is a shared activity, sometimes people have to be willing to give control to others on what their 'character' would do. Explicit game rules are not needed to enforce this! The most common type of shared-control is peer-pressure: "Come on guys, it would be sooooo cool if you did such and such. Think about it."
The literary equivalent of narrativist play is high-brow, critically assessed literature. Deep down, the author just wants to tell a cool story. (And also similarly, whether you're in high school English class or on the forge forums, it seems like the most boring incomprehensible thing in the world.)
GAMIST play is the feared bogeyman of the gaming community, but it's actually pretty harmless. GAMISM is about the thrill of playing to win, whatever that means. Tactical and strategic challenge, risk and reward, these are the what those players with gamist-preferences live for. After all you can't write "roleplaying game" without the word "game."
The literary equivalent of gamist play is a choose-your-own-adventure novel, preferably one with pulp detectives and vampires and ninjas and exploding speed boats.
Case Study Time:
So let's look at Prime Time Adventures. The idea behind the game is to simulate TV reality. So you might say 'AHA! PTA is Simulationist!' You would be wrong. TV shows are stories, and the goal of many players is to use PTA to tell the best dramatic stories they can. So you might say 'AHA! PTA is Narrativist!' Again, you would be wrong.
When people are using the tools PTA gives them to tell awesome TV-style stories, they're participating in Narrativist play. There are rules that definately facilitate this, but it all comes down to how you play.
When people are playing their characters and just showing off what they are like or what they might do, that's Simulationist play. This too is easily supportable under PTA.
Oh, and when people are trying to optimize the PTA resolution system to get their way, that's Gamist play. But that's hard to do in PTA, and I can't imagine having a PTA session that was predominantly gamist.
Cheers.