GSHamster said:
I kind of like the idea that strength and constitution are two different stats, but I'm not sure how realistic it is.
There's that word again. "Realistic". I don't want that in a game where I want to toss around fireballs or destroy things with my mind.
It's my pet peeve. Call it reasonable, consistent with the system, but "realistic" is always loaded with "very much like it would actually be in the real world". Things can be realistic but nonsensical for RPGs, or they can be reasonable but unrealistic. They can be both realisitc and reasonable or neither.
That having been said: It would not really be realistic - or reasonable - to combine them...
Morrus said:
A marathon runner would have a high CON, but not necessarily be physically strong.
Yeah, my uncle runs those things, and I could easily beat him up with brute strength (well, not really, but I always make him think so. Don't tell him this!

)
Okay, a lot of people could, probably. Send him to play with the fairies with one strike. But he could run the strong boys to death and not break a sweat (well, probably not quite like that, but something like that)
There's another aspect to consider: It would not only make no sense, it would also be a bad idea, rules-wise, at least in my opinion: Both are quite important abilities, most characters want decent Con, many want decent Str, and will give up higher values in other ability scores for it. If you turn it into one, it will be much cheaper for those guys to buy an 18 in Strongstitution and still get other stats.
Besides, if you combine Str and Con, what about Dex? And what about the mental scores? I'd rather fuse Wis and Cha - the new stat, Charisdom, would mean that you have a strong mind that can resist control by others and assert control over others, and awareness not only for sensual clues, but for empathic ones as well.
I don't say that I want Wis/Cha fused (I'd rather have some more ability scores than to get rid of existing ones), I just say that it would work better for D&D than Str/Con.