Previously, I talked about Baker’s idea of the “rollercoaster” that is Apocalypse World, whereby “real things, the dice and stats and so on, … give momentum to the fictional things”. I found his description pretty opaque , but managed to summarise it as “real-world actions are triggered from events in the fiction that are potentially interesting, and those actions make those fictional events more interesting”.
Mark Diaz Truman has since refined that a bit for me. He says Baker is talking about explicitly narrative momentum, a kind of energy in running game whereby a story is moving forwards. That doesn’t have to mean “following a pre-written story” ; it just means creating something that the players recognise as a story. As Mark puts it, it manifests as the “sense of making decisions that close doors and open other doors, of moving toward conflicts and decisions instead of just sitting and talking.”
In most games, the work of maintaining this energy lands on the GM, especially outside combat. PbtA rules, by contrast, often create momentum directly. Mark — “the moves themselves generate momentum. Even when you [trigger] a move and “things go smooth” a good move will generate new information and options that will pull you down the path of the story instead of just succeeding or failing on a test.”
In other words, the rules provide opportunities, building blocks, playing pieces, from which the the MC and players can build a story. And they put on pressure, rule out some things, make other seem natural or inevitable. This is often true even on 10+ (or 12+) results — PC successes can still have messy side effects.
As an example, Mark points to the basic move “Escape” from his Urban Shadows:
“When you take advantage of an opening to escape a situation, roll with Blood. On a hit, you get away. On a 10+, choose 1. On a 7-9, choose 2:
- You suffer harm during your escape
- You end up in another dangerous situation
- You leave something important behind
- You owe someone a Debt for your escape
- You give in to your base nature and mark corruption”
There, you can see that on any success something goes wrong in an interesting way, creating a story event, moving a story forward. It’s not necessarily the story anyone set out to tell, but it’s a recognisably a story and potentially an exciting one.
(Aside — notice how this operates on a larger scale than a typical roll in D&D, GURPS, or BRP. This is also typical of PbtA games — the single class of “moves” includes rules that operate over all kinds of different timescales. Indeed, many individual moves, like this one, can be interpreted on a timescale from seconds to weeks. This flexibility of scale is an important enabler for these momentum-granting techniques.
Illustrative counter-example — imagine trying to reconcile these kind of moves with turn-based combat.)
(Aside 2 — notice how that move is written in the language of stories, not just that of worlds and situations. Contrast that with typical OSR rules, which eschew story language and focus on concrete situations and logical consequences.)
 I find most things Baker says opaque. I like his writing, as a reading experience, but he invariably favours style over clarity, evocativeness over precision.
 And I wouldn’t be interested in a game where it did.