Also, via Joshua Newman's post "End", I read an Actual Play thread on Primetime Adventures: "END/Sexitricity", where Remi said that for the pitch "I insisted (quite strongly at one point) that there be NO negative input, only positive. I think that for a compressed game, this is the only possible way to eventually reach consensus. It also has the added effect of everyone adding information and no one getting denied on their Big Thing and disengaging.".
A similar subject came up on a Story Games thread on Forge Glossary stuff where Adam Dray explained about "Constructive Denial" -- a phrase used by Ron Edwards in a November 2005 Forge thread "ignoring the subjective" and elaborated on in another Forge thread "Constructive Denial?". Basically, this is a term for cancelling input that crosses certain lines of the game -- but it is tied up in conceptions of GNS Simulationism. cf. TheoryTopics Wiki entry for a summary.
So I discussed some about what additive play is in the Additive/Negational post. So, additive play is play where there is no negative input. If someone suggests something, that thing is accepted as truth. Everyone else accepts that and goes on to add other things to the fiction.
Taken broadly, this applies even to questions. For example, if in an improv scene, I were to ask you "Are you on your way to the Chesterfield meat market?" -- then the non-blocking thing to do is to say "Yes." By saying no, you would be shooting down my idea. By asking that question, I introduced the element of the Chesterfield meat market -- and additive play is based on the idea that each element should be used and built upon. In comic improv, you might respond with an elaboration like "Yes, I'm taking this ostrich there to be slaughtered." This accepts the meat market, and adds the ostrich.
In Paul's podcast, he expressed that one of the problems of blocking in improv was that it can turn into a status clash -- where the actors are trying to put down or deny other actors' input. I think that is true, but there is also plenty of room for status clash within additive play. Actors vie to dominate the scene by jumping in first to define more. By keeping a steady stream of output, a fast-talking improv actor can easily dominate others in the scene.
This rewards aggressiveness and speed of judgement in terms of the social discourse. This is a good thing in many ways. It means that you have fast pacing, and that you will likely get through any resolution quickly. However, the only way to have limits is for players to understand in advance what the lines are and not go over them. By definition it would be non-additive to block, if something goes past limits, then it is negational to block them.
It also can end up skewed pretty far from what you would get by consensus.
Negational play means that someone can put a stop to something that someone else said. Good example are the phrases from Polaris: "You Ask Far Too Much" and "It Was Not Meant To Be" and "It Shall Not Come To Pass".
In a two-person exchange, status conflicts seem similar to additive but slower paced because more assertions are denied. However, among a larger group there is an important group difference. In additive group play, the person fastest at asserting dominates. In negational play, there is a veto power. If other players can negate -- especially if multiple players can negate -- then you can stick closer to what everyone likes.
The point is that it is easier to negate than to create. If someone isn't a fast creator, then they'll simply be overshadowed. Negation -- either by a gamemaster or by some sort of group actions -- allows the more creatively dominant players to be reined in.
Tabletop Resolution Systems
For the most part, dice-using resolution systems -- and even other ones -- are negational. One side or the other is negated in favor of some other result. If there is some sort of suggested goal that was being attempted, then failure to achieve the stated goal is negating that element -- i.e. blocking the person that suggested it.
I suspect the idea of non-blocking will be strange to many tabletop role-players. Even among the indie games, there are still generally conflict resolution systems that can end in the failure of someone's suggestion. In improv terms, this is blocking, regardless of the scale of the resolution (i.e. "I shoot... You miss!" or "I try to kill him... You fail!").
There are some systems that can be used in an additive fashion. Amber and Everway, for example, are systems that don't have any mechanical definition of failure. You can play that everyone succeeds. Everway's tarot card system allows there to be colorful results from a suggestion that don't deny introducing it.
I haven't tried it, but (via Paul Tevis' latest Have Games Will Travel), Joshua Bishop-Roby's Sons of Liberty sounds like a more additive system as well.
As I consider these two approaches, it seems like what is primarily at stake is (1) keeping up pacing; vs. (2) balancing player input.
In my experience, this has been an art rather than a science, especially #2. If I am GM, I'll try to draw in the less active players and rein in the more dominant ones. If I am a player, I'll draw out less active players by having scenes with them and not pick up as quickly on what dominant players want.
One way to control additive dominance without negation is by strict turn-taking. However, the result isn't necessarily a best of both worlds. For example, there is Ferry Bazelmans' Soap: The Game of Soap Opera Mayhem where everyone takes a turn adding in a sentence. A similar mechanic is the newsreel in Lee Short's The Star, The Moon, and the Cross, where each player picks a tarot card and adds it to the sequence. In practice, though, this means that pacing is blocked -- because often someone will have trouble coming up with something on their turn.
Still, it is something to consider.
I have other thoughts on this, but I think I'll first toss the reflections out there for comment.