To me, a better idea is to say, "Knocking something prone means knocking it down," and if you try this on an ooze, the rules are basically like, "Well, DM, what do YOU think happens?"
That's one way to go - as has been pointed out, though, it can lead to PC-nerfing.
A different approach is to frame the rules in terms of generic/abstract "complications" or "disadvantages" and then to allow the details to be spelled out at the point of application (MHRP-style).
As was discussed upthread, 4e is a sort-of halfway house between the two. (Presumably so, like D&Dnext afterwards, it could accomodate either preference.)
It's clearly easier (or it should be in my opinion) to disadvantage a sentient, vertebrate humanoid than a mindless, formless puddle.
In D&D shouldn't that be etablished via AC and other defences, at least in the first intance, rather than via immunities?
How about rules that use words that clearly and narratively describe what happens instead of inventing rules that require us to provide narrative justifications for effects?
I think this just illustrates that there is more than one way to approach the issue, and it seems to come down to a matter of preference. Some seem to prefer that the story should flow from what the rules say are happening, while others would prefer the rules are only there to support whatever story it is you want to tell.
Ron Edwards got the contrast in approaches pretty clear, in my view.
First, (what he calls)
simulationism:
Consider Character, Setting, and Situation - and now consider what happens to them, over time. In Simulationist play, cause is the key, the imagined cosmos in action. The way these elements tie together, as well as how they're Colored, are intended to produce "genre" in the general sense of the term, especially since the meaning or point is supposed to emerge without extra attention. It's a tall order: the relationship is supposed to turn out a certain way or set of ways, since what goes on "ought" to go on, based on internal logic instead of intrusive agenda. Since real people decide when to roll, as well as any number of other contextual details, they can take this spec a certain distance. However, the right sort of meaning or point then is expected to emerge from System outcomes, in application.
Clearly, System is a major design element here, as the causal anchor among the other elements.
Then, non-simulationist play, which Edwards categorises as either
gamism ("step on up") or narrativism ("story now"):
Step On Up is actually quite similar, in social and interactive terms, to Story Now. Gamist and Narrativist play often share the following things:
. . .
* Fortune-in-the-middle during resolution, to whatever degree - the point is that Exploration as such can be deferred, rather than established at every point during play in a linear fashion.
* More generally, Exploration overall is negotiated in a casual fashion through ongoing dialogue, using system for input (which may be constraining), rather than explicitly delivered by system per se.
Now what bogmad is advocating is what Edwards describes in the first paragraph: internal cause is king, the function of the mechanics is to model ingame causatin (eg "knocking prone", as a rules element, means that the character does something, like a polearm sweep, that knocks the target of its feet), and the "story" - the ingame fiction - is dictated by the mechanical resolution (if the polearm sweep succeeds, then the target is on the ground!). In a rules sytem like this, if something has no feet than it can't be knocked over, and that should be reflected in the mechanics (try your polearm sweep against an ooze, and you'll automatically fail).
Whereas Nemesis Destiny is expressing a preference for mechanics that
constrain the details of the fiction (eg if you hit with the polearm sweep, some complication or disadvantage for the enemy has to be narrated) - but they don't determine those details. These are "negotiated in a causal fashion" by the participants, within the constraints imposed by the system, but not relying on the system to deliver the content of the fiction in a determinative, linear, way.
My guess would be that bogmad doesn't like "Schroedinger's wounds". My guess would be that they don't both Nemesis Destiny because Nemesis Destiny doesn't mind it when "exploration" (ie actually settling the details of the fiction) is deferred, and "casually negoiated among participants"
after the action has been resolved relying on the mechanical outcomes as constraining but not, on their own, determinative.
Two different approaches to RPGing. Some mechanics can straddle them (eg hit points - compare "meat" interpretations to "meta" interpretations) but many can't (eg the 3E grapple rules, the 4e death and dying rules).
