I got serious pushback on the system as theory post, the thrust of which was that I failed to establish that tabletop role-playing games systems are like scientific theories, because I didn't show how they provide predictions.
My immediate response was very defensive: that I should probably go and revise the post significantly if it could so easily be misconstrued to mean that I'm talking about scientific theories in the sense of being able to perform exact predictions to begin with. I only brought up physics to expound on my academically-fueled view of theory, in terms of utility rather than truth, and then to apply it to theory in media studies, which I saw mostly as a tool for comparisons. I didn't use the term "prediction" at all.
But with more thought came a realization that maybe it is fruitful to think of prediction in systems as theories of play. If my system is Dungeons & Dragons, then I can predict that the games that I play will involve hit points, experience points, weapons, magic, monsters, dungeons, and all of those artifacts that comprise the interactable building blocks of the game, and that I as player and/or dungeon master will use them or be used by them in certain ways. And if it is, indeed, a session of D&D, these predictions will likely come to pass, and I will be able to make some determinations as to the quality of the participants and the way the whole thing went.
If, on the other hand, I take these D&D-laden predictions to a game of Blades in the Dark, they will run counter to what I actually experience. The classes - sorry, playbooks - won't really correspond to anything I'm familiar with, nor will the ability scores and skills - sorry, Action Ratings. What's this Harm? Is that like HP? But that should increase with level! Where are levels, and what are these separate experience tracks? Are you really only getting a handful of points each session? Why do I have contacts on my sheet? Wait, we're rolling to figure out how an adventure starts? I want to plan! Flashbacks? You mean, whenever I run into a situation I don't like I just get to make things up so it's actually fine? Where are the combat rounds? Why is the DM - sorry, GM - not rolling attacks for the enemies? Why is the GM constantly asking me questions about the world that they're supposed to answer if they know what they're doing? This is not in the ballpark of what I was expecting, of what my theory of play predicts that a session will look like.
This experience, and the way it diverges from my predictions of how a game would play, could then lead me in several directions. The simplest reaction would be to withdraw to my existing theory, chalking it up to a bad group, or bad DM, or a bad set of circumstances for this particular session. On the other hand, it might push me to revise my theory, expanding it to include forms of play like D&D and Blades as special cases.
But if we take the prediction aspect seriously, it might not even come to that. Because if somebody tells me a little bit about how a Blades session goes, it's going to be so different from anything I would expect from a successful D&D session that I might just not ever try it at all. And I think that's at the heart of why the rising tide of D&D 5th Edition is not lifting all TTRPG boats.
In my case, I was lucky: my first exposure to TTRPGs was in the 1990s, when the local gaming magazine presented D&D (then Advanced D&D 2nd Edition, for the most part) as just one of many existing TTRPGs, ranging from Rolemaster to Shadowrun. Even though most of my experiences were with AD&D 2E, my theory of play didn't hold it as the end-all and be-all of that thing we did.
Unfortunately, as D&D 5E has been presented and marketed, at least in the anglophone West, it's very easy for newcomers to the hobby to not really be exposed to other systems as real alternatives in a wider context of play. This is made worse by the Open Gaming License, which allows a certain variety of other games which nevertheless point back to D&D as their baseline, the original game with the highest production values. I think that's a real barrier to a lot of alternative games, large and small. It's also cheating the people playing D&D 5E, especially DMs, out of a wider variety of experiences, and maybe "system as theory" helps explain why they don't see it that way. I do think there's more to it than that in the specifics of the system's mechanics and (lack of) DM support, but that's for a future post.