I'll agree that Physical/Mental/Social or Body/Mind/Soul is an extremely intuitive and satisfying (and narratively resonant) division that covers most of the human experience. I use it myself in some of my homebrew systems.
However, if you wanted something based on '21st century science', there would only be one domain: physical. Mental phenomena are a product of the physical brain. Social phenomena are mental phenomena mediated through physical spaces and interactions, etc.
quote:
But I still think those three broad categories cover pretty much all human skills, and would work well as modiifiers to specific skill scores
I'm not sure they would. As people have pointed out above, different sorts of, e.g., physical feats (lifting heavy things, sprinting, endurance running, tolerating pain, resisting disease, manual dexterity, flexibility) all require different qualities that are often only loosely related or actually counter-productive to one another.
Likewise, mental feats such as abstraction, deduction, induction, spatial awareness, memory, etc., are not so connected that you can base them all off the same stat and say you're modelling reality.
As a game mechanic, sure, these three domains are good enough for play, but you can't really claim they're 'scientific' or 'realistic'. But they feel right to most people, I'd wager, which is more than enough.