[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... partly because it's a good way to get my thoughts straight.]

This follows on from the post in which I explained, to my own satisfaction at least, how trees / graphs aren't always the best way to manage your interactive story. Short version: trees are intuitively comprehensible, but fragile. Rivers are more robust, especially in a collaborative story, and allow players to decide in which order they want to make their decisions.

Some folk suggested on blog comments or Twitter that the difference between trees and rivers is one of scale: that if you look at a river close enough, it's all trees. Floating in the current, perhaps. Well, *ish*. Certainly, if you break down a story far enough, the atoms are decisions. A storylet in Jonathan, the engine behind Echo Bazaar, is a single-level tree with a root, branches and leaves. Trying to use these as the basis for planning is (to over-use a metaphor I often over-use) like dumping out a bucket of mosaic tiles on a table and trying to assemble them without a guide. Sometimes (as with the later stages of the Jewel-Thief romance in Veilgarden) we do fit them together into a larger tree structure: sometimes, as with the earlier stages of that same romance, it's not a tree at all. It's just mosaic tiles floating downstream, loosely arranged in a constellation of things which are generally constrained to happen together.

(In Varytale, as it happens, a storylet *can* have a more complex structure: we can branch and branch again, rather than needing to build a tree out of separate atoms. You could put a whole CYOA inside a single Varytale storylet if you really wanted. But you really shouldn't.)

Anyway: I wanted to talk about different kinds of event. Compare 'a monkey punched me, bruising me badly' and 'my beloved monkey punched me so hard that I decided we part ways.' The first is always an explicit element in the story... the second may or may not be. Perhaps it's a scripted story event, but perhaps you simply get an unlucky Monkey Response roll and decide to sell the little villain, in which case it's an implicit story event, one you've decided the relevance of yourself.

Implicit story events are the gold nuggets in the narrative mine. They're marvellously powerful because you've co-opted the player into the story; they're necessarily rare because they have to be heavily outnumbered by explicit story events. We're talking here about moments of imaginative freedom in a curated story, not a drama workshop or a tabletop RPG[1].

Implicit story moments are like a spark jumping between two explicit events. You can't guarantee them. Perhaps it's just going to be a gap. But you can work to induce them. This is what we mean when we talk about fires in the desert and reflective choice.

A river story is a semi-directed montage. All narrative, even interactive narrative, is edited and arranged, but if you compare a traditional game to a film [2], or a texty game like EBZ to a book, there's always less directorial control over pacing. In a tree, you get substantially more control - that's one of the advantages - but fewer gaps and, consequently, fewer sparks.

So river stories, as I said last post, are more robust in the writing, but they can also be more robust in the reading. By keeping the story moments in a more flexible arrangement, and by allowing space for moments of imaginative freedom, you encourage reader commitment and invite the reader to co-operate with you in the suspension of disbelief. If you want explicit story events explicitly glued together, a tree is a better choice, but it limits engagement: powerful, but brittle.

We could go a step further than all this, to city lights. But I'll talk about that next time.

[1] And both those things are fine. They're just not what I'm interested in here.

[2] It's fashionable to point up the differences between film and AAA games, and certainly the Michael Bay style of blockbuster has been a pernicious influence. But AAA games *are* more like film/TV than paintings novels sculpture theatre architecture... you can argue this is because they happen to happen on a screen, but then you'd also have to concede that their location on a screen for the last forty years has influenced the techniques and terms we use: cut scene, camera, bullet time.