Linearity: Progressing from one stage to another in a single series of steps; sequential.
Non-linearity: not sequential or straightforward.
Gaming is an interactive medium, and as such, one of the key elements a game should transmit to the player is the sense that their input somehow affects what is happening on the screen. From making a line disappear in Tetris to throwing a person flying in the air after punching them with a giant dildo in Saintís Row 3, feeling like you are the direct cause of something that happened ingame is satisfying and is crucial for immersion (thatís a word for another day). This is relatively easy to achieve when a game is purely mechanical, such as sports games, driving games, twin-stick shooters, fighting games... When a game is trying to deliver a narrative, on the other hand, things get complicated.
Narrative usually includes text, either literally or in the shape of dialog or audio logs, and that text is written by writers. That means that the more freedom is given to the player, the more text will have to be written to react to that playerís actions. Realistically, it means that more freedom to the player will result in the NPCís reacting unrealistically to the playerís actions or simply not acknowledging them at all.
But we like stories, no, we love stories. Stories keep us engaged when repeating the same action a million times or the pretty graphics arenít enough. Good stories make us connect with the characters that surround us, they stimulate our imagination and make us emotionally invested. Thatís why they have a place in any form of entertainment, because theyíre a crucial part of our nature. So the ultimate challenge for videogames today is finding the sweet spot between telling a story and making the player feel like their actions have direct gameplay consequences. Hereís when the concept of narrative linearity comes into play (pun intended). Telling a written story directly interferes with player interaction, given itís limited nature. That is unless you make the story itself interactive. Generally speaking there have been three approaches to this problem:
1-Separate gameplay and narrative sections entirely, through the use of cutscenes or text.
2-Deliver narrative through audio logs, environment objects or npc dialog.
3-Make the player active in the narrative delivery via dialog choices.
Most games have a linear narrative, delivering their story through a mix of examples 1 and 2. The problem with it is that it usually interrupts player interaction. But recently a significant number of games have opted for the 3rd choice, to let the player ďchoose their own pathĒ.
Now, videogames are based on an illusion of freedom; you give the player a set of tools, environments and gameplay elements to play with. Player enjoyment is directly related to how solid, consistent and believable those systems are. The bright side about linear narrative is that it provides a sense of cohesion that just canít be achieved through player choice. As weíve already established, giving the player too much freedom only makes his lack of freedom more obvious. Of course every choice the player makes in a non-linear game canít have a truly believable set of consequences, and the number of choices the player has is rather limited, because the game is made by a limited amount of people in a limited amount of time with a limited amount of resources. Even if a game just offers several narrative arcs to arrive at the same conclusion, it is still a non-linear game. Linearity is about the sequentiality of the path, not the conclusion.
I think itís fair to argue that videogames still havenít found their own language when it comes to delivering stories. Weíve become used to watching cutscenes between actual gameplay as a way of mixing things up and making us feel at least a bit emotionally involved, but I think we can all agree that todayís standards for storytelling in videogames are far from ideal. In response to that feeling, the general trend is towards narrative that is somehow affected by the playerís decisions, but some games have decided to avoid traditional narrative altogether.
Okay, weíve already established that linear games are those that make you progress from one stage to another in a single series of steps. Non-linear games, on the other hand, are those that give you several steps to choose from, even if they do all end up in guiding you towards the same stages. The tendency towards including player choice in the narrative has also made an appearance in gameplay mechanics, with games that were traditionally extremely linear giving the player some options in their latest iterations (like CoD: BlOps 2) that even if rather limited, are just a sign of a bigger trend towards palyer freedom, better exeplified by games like Dishonored or Far Cry 3.
This is a fundamental change in the way we understand games; no longer are they toys designed with specific functions in mind, but entire playgrounds with dozens of options that let the players express themselves through the way they decide to play. Minecraft, Day Z, Dwarf Fortress, Proteus... those are games that donít bother with feeding the player a specific narrative, they just give them the tools to create their own experiences. Not only does that mean different experiences for every player, but the stories that flourish from those experiences feel more genuine because the games feel more genuine. The player feels like his actions are the direct and only cause of the events that surround him, and thatís what true freedom is all about: Not only choosing your own path, but building your own path with your bare hands; weíre moving past non-linearity and towards pure freedom.
But where does traditional narrative fit in that picture? Will we have a separation between narrative-driven games and player-driven games? I donít think so. What I see coming is a sandbox of sorts. The creation of those forever-mentioned ďliving, breeding worldsĒ. Worlds where stories happen all the time, and you can choose to have an impact on them, observe them or just ignore them altoghether. Iím not only talking about MMOís, which I think will have an important paper in the future, but also procedurally created sandbox games, with so many options that the player-created stories would be endless, and traditional stories would be just one option from the menu, culminating the ideal of player freedom. While games with high production values would focus on offering a lot of different options, less expensively-produced games would focus on offering worlds that were out of the ordinary.
Okay, maybe thatís a bit crazy. Maybe Iím just exaggerating and itíll all keep going as it is. Iím not saying that is the future Iíd like for videogames, it just seems like the natural progression from the perspective we have today. Damn, Iíve gone on a bit of a tangent here. Oh well, whatever.
Edit: Here are some videos I digged up that I think are relevant to the discussion (I don't necessarily agree with all they say, but they make some good points):
Errant Signal (not actually about linearity but it poses some good questions about the future of videogames)