[This is one in an intermittent series of posts about internal FBG terminology. Partly because we use these terms in the wider world sometimes, partly because it might have more general implications. This post is also about my ambivalent relationship with the tree as a model for how to think about interactive stories.]

Trees (directed graphs, flow charts, all their cousins) are a natural way to think about stories. You make a choice, you make another choice, you make another choice... you reach an ending. You can trace your path back clearly from your final ending to the beginning. If you've ever tried to conceptualise or visualise a story from a height, you probably drew a tree.

But only a minority of interactive stories (eg hypertext narrative, the classic choose-your-own-adventure style of gamebook without the refinements of later gamebooks) are really just tree stories. Partly this is the notorious issue of combinatorial explosion: trees can't just keep branching indefinitely for the length of the story! So we merge some branches back into others (which only feels like a cheat when you notice), or we create some sort of state (Stamina, Dark Side Points, inventory items, ... Connected: the Duchess) that decisions can affect. Even quite tree-ish narratives are rarely pure tree. But partly it's because most interactive narratives are different in an important respect: you have a choice about when you make choices.

This is the fundamental property of a river story. In a pure tree, each choice is followed by a predetermined next. In a river, you have some degree of control over when you make what choice. It might mean that you're navigating a textual space where the use of verbs has some geographic texture, as in traditional IF, or exploring a map full of canned encounters, as in a classic CRPG. It might mean that you're picking from a menu of storylets, as in Echo Bazaar.

This fundamental property often gets called 'non-linearity' in game reviews, and that often leads to disappointment. When we call something non-linear we suggest that it's not a story in the traditional sense, because a story has a beginning, a middle and an end. It is very hard to make satisfying stories, interactive or not, that don't have a definite beginning, middle, and end. It's arguably not impossible: just difficult and not necessarily worth the effort.

The river, then, has a beginning, middle and end. The end may be multiple endings, but you're basically being funnelled through a similar landscape to everyone else on the river. That's all right. Your experience can be fundamentally different, just as the experience of a hundred people travelling the same ten miles of road can have be different, depending on who tripped over what donkey or who met their lover when or who was robbed and who hid behind a boulder. And your internal experience may be much more radically different, especially where the story is something that allows for interpretation.

This is a significant tension at the heart of interactive stories. A story is a series of things happening in a particular order: it's the order that makes it a story. But in a riverine interactive story, you choose what order things happen in! Tree stories resolve this by not allowing you to decide the order. River stories keep their beginning, middle and end, and they also keep floes or islands of relative inflexibility in the middle.

Of course I'm conflating different kinds of event here, I know: 'a wandering monkey punched me for five hit points of damage', 'I remember a monkey punching me in my youth', 'my beloved monkey punched me, ending our friendship forever', 'the inevitable monkey punch occurred in the pantry rather than the parlour', and so forth. Next time I'll talk about that, about internal experiences, and about city lights.