Thanks for the interesting post. For what it's worth, I, like all armchair designers, have been intrigued by "symmetrical" attributes – physical, mental, maybe even "spiritual" – but in the end, I didn't keep that interest. I never did come across some scheme that always made perfect sense. And more to the point, I find I don't even care much for the artificial labeling of certain traits as attributes, while countless other traits are arbitrarily placed under advantages, features, sub-attributes, or other labels. It all raises questions: Why isn't, say, Charisma an attribute? Why is ST an attribute, when it's so different from the other atts in many ways? And so on, with the apparent answer to any such question being "RPG convention" or "designer whim".

Nothing wrong with that in terms of play, but it leads me to not fuss over the identity or essence of attributes. These days, I like a nicely fuzzy, all-encompassing "traits" label that everything falls under, without unneeded distinctions.

But stepping down from that soapbox, you have an interesting take on symmetry in atts. Given that a set of defined atts is the norm in RPGs, there's no harm in pondering new ways of looking at them, so let's do that:

Your suggestion of IQ as a physical attribute is interesting, as is your new categorization: not physical and mental, but "used for skills (IQ, DX)" and "used for non-skill, physical purposes (ST, HT)". I like the unique approach.

You're also looking for symmetry in making use of combinations of atts – that, too, is an approach I haven't seen before. You want the game to equally find some use for every added pair of two atts, correct?

Well, you're right that some combinations get no or little use: ST+IQ, or ST+HT, for example. Now, this is also somewhere where I personally don't see a need for the symmetry you're looking for, but if you want it and can find it, good for you.

I agree that IQ+DX is a very natural combination to represent reaction speed, if you create rules calling for that. As for ST+DX, it might make some measure of overall combat prowess, again if you can find some way to use it. But as for ST+HT as the base for Speed: well, as I've said elsewhere on the site, and as you note as well, that combo gives bad results unless you also account for weight. Though it seems to me that you'd be breaking symmetry by doing so, essentially basing Speed on three traits, not two.

That becomes an example of why I think it's impossible to get some perfect symmetry, and why I no longer look for it... but if you find a new solution to symmetry that we've all just missed so far, that'd be worth hearing about. If it's of interest to you, please keep at it!