| Chapter 10: Scenes |

| 10.9. Why are scenes designed this way?

In the part it plays in stories, time is like space. The endings of a scene (along with its beginning) are like the map connections leading out of a room. The Scenes index keeps track of the "map of time" through which these possible story-lines traverse. Some works of IF will have immensely complicated story-lines in only a few rooms, some will have no scenes at all despite a sprawling geography. The Scenes and World index tabs, side by side, show both kinds of map.

Just as Inform uses a simple but practical design for the boundaries between rooms (map connections and doors, that is), it also simplifies transitions between scenes. Scenes are based on states of things: we give circumstances for them to begin or end. There is no phrase with the power to say "make Act II begin right now", so perhaps it is worth explaining why not. The state-based approach was chosen because:

> * it guarantees that each action falls entirely inside, or entirely outside, of any given scene (and therefore that "during..." clauses in the conditions for a rule are not affected by rule ordering);

> * it ensures that scene changes occur outside actions, like every turn rules;

> * it promotes a style of writing which makes it clearer to the reader of the source text when a scene begins and ends, and what conditions are guaranteed to be true during it;

> * it makes it possible for the Scenes index page to show this information in a communicative way.

Settings in IF where one revisits the same location but at a different time, or after a dramatic change, have historically been difficult to test properly and prone to mistakes. (The classic example would be where a character killed during Act I reappears unharmed in Act II.) The design of scenes is an attempt to encourage a style of writing which minimises the risk of these accidents.

Since scenes are, in the end, only a convenient way to organise rules, and do nothing that cannot be done by other means, this simplified system of scene changing does not really restrict us.

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