I think a better mathematical model than a continuous space (avoiding technical math here) would be something like a directed graph. Now, you can then evaluate the games and kind of position them near or far based on how you perceive their play, or your play of them, to be similar or different. That won't produce a neat graph though where all the things you like are both clustered in 'preference space' AND fall on the same part of the graph! I mean, OK, the two may even correspond a reasonable amount due to a 'school effect' (IE people who participated in the Forge and developed games based on or influenced by AW, so a lot of Narrativist preference space may also cluster close to AW on the 'got bits from' graph).
Right. On your proposed graph Burning Wheel will be related to the RQ/RM approach to design (long skill lists, derived attributes, "realistic" combat, etc) but also to Prince Valiant and HeroWars/Quest (both simple and extended contests, intent as a key factor in resolution, early approximations to "say 'yes' or roll the dice") and will also have some innovations of its own ("let it ride).
So (i) the graph will be complex, and (ii) it will not put BW and DW in the same neighbourhood, even though we can predict at least some overlap in their fan base, and probably more than the overlap between BW fans and RQ fans.
(I mean, maybe your new TV borrows some clever bit of design that was first used in a bit of high-end hospital equipment. That doesn't mean that you, as a TV watcher, are suddenly going to go out and buy some sort of body-function monitor just because it bears some technical resemblance to your TV.)
I want to keep reinforcing this, even within a play style preference, like Narrativist, there are just things that have no intermediates. I don't see how you can take PbtA and mix it with 4e and get something halfway in between. I mean, I went through this exercise, trust me, and it just doesn't really work. HoML has some ideas that reflect experiences with PbtA and such, but it is still pretty much built around a 4e-like chasis, you just can't mush together moves and skill challenges! There's no halfway point between those!
Yes, I said the same thing upthread. Even with games that are likely fairly close on the imagined graph, there may be no intermediaries. I gave RQ and RM as one example: either attack and defence are rolled separately, or are allocated by the player from a common pool. The presence or absence of that player choice is a fundamental difference between the way the two games resolve melee.
RuneQuest: Roleplaying in Glorantha has Passions.
My understanding is that this is a fairly recent publication. I was talking about the classic version of the game, which went through various iterations in the 1980s. Apologies if that was not clear.
Although intriguingly something like Passions first appear on the NPC record form for Griffin Mountain, (c) 1981 in the edition I am looking at, and thus four years before Pendragon was published.
I'm finding it hard to parse out your meaning. Did you mean that adding Passions to the main text of RQ is a tremendous change? It can be, depending on how a group use them.
I don't have a copy of Griffin Mountain. But personality guidelines for NPCs - which (presumably) the GM is expected to adhere to in playing those NPCs - is not the same as Passions for PCs. Pendragon's Traits and Passions act as constraints on (and also generate incentives for) the players' play of their PC.
This is a tremendous change to how players play their PCs. It was recognised as such when Pendragon was published. It is still widely regarded as a big deal now, as best I can tell.
(I don't know what the contemporary RQ text says about Passions, or how they are to be used. But if it tells the players of the game to use them in the same fashion that they are used in Pendragon, then yes, that is a big change. If they are presented as an optional sub-system, then players of the game are being presented with an option to make a big change in how they play compared to "default" RQ.)
The many, many game texts riffing off one another and drifting are themselves proof.
I am talking about RPG systems - ie actual procedures and techniques of play - not RPG texts. So is
@AbdulAlhazred in what I have quoted in this post.
I don't know what you mean by talking about game texts "drifting". But RPG text have riffed off each other since the first RPGs were designed. This doesn't show that for any two arbitrary RPGs, there are arbitrarily many intermediate forms.