Theory post. It’s been a while since the previous one.
Fruitful void is a concept for designing and analysing games. Let us take some roleplaying game and assume it has rules. Fruitful void is something the rules do not cover, but point towards.
With D&D 4e rules give you plenty of maneuvres in combat so that significant number of them are interesting, but the rules do not tell which one you should use. There are characters whose powers can work well together, but the rules do not tell how to use the powers so that the synergy benefits manifest. Dogs in the Vineyard is about judging people, about how much violence one is willing to use to do what is right and about faith. There is no faith attribute (that judgment is for the players to make), there is no rule telling that you must use violence and there are no guidelines about what judgments are appropriate. That’s up to the players. Old D&D gives lots of tools for dungeon delving – combat ability, spells, items, henchmen – yet there is no skill for making tactical and strategic decisions. Those are up to the players. Burning Wheel has involved rules for fighting (in melee, with ranged weapons, with words) and lots of other rules that make other parts of gameplay or story move fast. And when fighting the player must script actions – high numbers on character sheet are not sufficient. The tactics and what one fights for are up to the players.
So: Fruitful void is the space a game leaves for players to fill, and towards which the game points players. The concept applies well to focused games and less well to GURPS or (certain) games which get out of the way. The concept applies weakly to games that take a life of their own (which, I reckon, is related to getting out of the way). The comments on Anyway relating to the subject are worth reading.
Lever as a concept was introduced by d7 just a while ago. Lever is some mechanical tool a player can use to affect the fiction. Skills, powers, aspects, so on.
I think these two concepts are related in more than a single way.
D7 uses diplomacy skill in D&D 3rd as an example of a lever ill placed: It negates all negotiation by skipping it with a single skill roll. That is bad if you want to have a game where negotiations are central. Point: Levers can certainly kill a fruitful void by bypassing it entirely. Consider: Play modern D&D, but instead of using the combat rules simply add a fighting skill and resolve all combats by rolling it. Not much point in playing modern D&D that way, is there?
Levers can skip boring parts of gameplay. This is what many skills in BW do. This is one way of seeing diplomacy on D&D 3rd. Of course it is also possible to handwave those bits away, but often the rules are useful.
Using levers can be the fruitful void. This is 4e. There is much GM advice on building interesting combats, which simply means that there is no universal best tactics – add environment factors, terrain, varied enemies with special powers and so on to change which tactics are functional and to what degree.
The decision to pull or not pull a lever can be in the void. Tactical version: You have one sleep spell per day. Use it now or later? Dramatic version: You can summon demons, but they demand a high price. Whichever version: You know magic, but there’s a chance it goes horribly wrong whenever you use it.
I’m sure there’s more. An exercise for readers.