Emergent narrative, a term introduced by designer Marc LeBlanc in his lecture "Formal Design Tools" at the 2000 Game Developers' Conference, refers to storytelling produced entirely by player actions and in-game events (LeBlanc, 2000). Emergent narrative storytelling does not contain narrative blocks (which he calls embedded narrative) created by a writer. The story emerges from the act of playing. There is no separate storytelling engine and no preplanned story structure, either linear or branching; in principle, anything can happen at any time so long as the core mechanics permit it.
Playing The Sims can create emergent narratives because the game simulates the activities of a group of characters and contains no prewritten narrative blocks. However, The Sims is not really a device for telling stories to the player because it gives the player so much control that he doesn't feel as if he's interacting with a story but rather that he's creating a story. The game is more of an authoring tool. (See Chapter 5, "Creative and Expressive Play," for further discussion of player storytelling as a form of creative play.)
The chief benefit of emergent narrative is that the sequence of events is not fixed by a linear or branching structure, so the player enjoys more agency. He can bring about any situation that the core mechanics will let him create. However, the player can control the story's events only to the extent that he can control the core mechanics through his play. If the designer sets up the core mechanics in such a way as to force a particular situation on the player, his experience can be just as restricted as in a foldback story.
LeBlanc himself points out that emergent narrative is not without its problems. For one thing, it requires that the core mechanics be able to automatically generate credible, coherent, and dramatically meaningful stories—an extremely tall order. Core mechanics are defined in terms of mathematical relationships rather than human ones; how can they produce reasonable human behavior? How can you make them generate emotionally satisfying stories algorithmically? At the moment, with the field in its infancy, nobody knows. Furthermore, the core mechanics must limit repetition and randomness, and at the moment, the core mechanics of most games produce a lot of both. Finally, emergent narrative seems to offer nothing for conventionally trained writers to do, and it might not be wise to give up on ordinary writers just yet, given the millennia of storytelling experience they represent.
The best information available right now doesn't reveal the existence of any commercial games that make use of purely emergent narrative without any embedded —that is, prewritten—material. The industry does not yet have any software that generates stories good enough for commercial entertainment products. At the moment, emergent narrative remains an experimental technique, part of an AI research field known as automated storytelling, which offers great potential for the future.