Linearity (computer and video games)

A video game with nonlinear gameplay presents players with challenges that can be completed in a number of different sequences. Each player may see only some of the challenges possible, and the same challenges may be played in a different order. Conversely, a video game with linear gameplay will confront a player with a fixed sequence of challenges: every player sees every challenge and sees them in the same order.

A nonlinear game will allow greater player freedom than a linear game. For example, a nonlinear game may permit multiple sequences to finish the game, a choice between paths to victory, or optional side-quests and subplots. Some games feature both linear and nonlinear elements, and some games offer a sandbox mode that allows players to explore an open world game environment independently from the game's main objectives, if any objectives are provided at all.

A game that is significantly nonlinear is sometimes described as being open-ended or a sandbox, though that term is used incorrectly in those cases, and is characterized by there being no "right way" of playing the game. Whether intentional or not, a common consequence of open-ended gameplay is emergent gameplay.

Games that employ linear stories are those where the player cannot change the story line or ending of the story. Many video games use a linear structure, thus making them more similar to other fiction. However, it is common for such games to use interactive narration in which a player needs to interact with something before the plot will advance, or nonlinear narratives in which events are portrayed in a non-chronological order. Many games have offered premature endings should the player fail to meet an objective, but these are usually just interruptions in a player's progress rather than actual endings. Even in games with a linear story, players interact with the game world by performing a variety of actions along the way.

More recently, some games have begun offering multiple endings to increase the dramatic effect of moral choices within the game, although early examples also exist. Still, some games have gone beyond small choices or special endings, offering a branching storyline, known as an interactive narrative, that players may control at critical points in the game. Sometimes the player is given a choice of which branch of the plot to follow, while sometimes the path will be based on the player's success or failure at a specific challenge. For example, Black Isle Studios' Fallout series of role-playing video games features numerous quests where player actions dictate the outcome of the story behind the objectives. Players can eliminate in-game characters permanently from the virtual world should they choose to do so, and by doing so may actually alter the number and type of quests that become available to them as the game progresses. The effects of such decisions may not be immediate. Branches of the story may merge or split at different points in the game, but seldom allow backtracking. Some games even allow for different starting points, and one way this is done is through a character selection screen.

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