Blue Orange
Gone to Texas
It depends a lot on what you're trying to do--the easy answer is 'homebrew to your taste'. If you're theoretically redesigning the whole system, the problem is that once classes hang around for a while they tend to develop archetypes people want to play, and then you're stuck slotting those into one of the ability scores as 'prime requisites'...er, associations. Sometimes they fit, sometimes they don't.
I actually studied (informally) a bit of Hermetic stuff as research for a never-written fantasy novel, and sometimes the correspondences lined up pretty cleanly (fire, iron, red, Mars, war) and sometimes they had a list of things and you could see they were just trying to fill out colors, elements, etc. (Green is copper because of the patina on copper...fine, but then blue is associated with tin and Jupiter why? Wouldn't purple, the royal color, make more sense? The main ore of tin, cassiterite, is black, but you already used that for lead, which actually looks more bluish as a metal... why isn't copper red, the metal itself is, oh wait you took that for iron.) You have a similar problem with the Chinese elements, though there they had a system of relationships they were trying to fill out too--I can get that water puts out fire and gives rise to wood, but the bit about dew collecting on metal in the morning strikes me as an obvious bit of Procrustes.
You wind up getting the same sort of effect when you try to tie each class to an ability score. OK, wizards are smart and fighters are strong since 1974. Bards really should be charismatic and rogues dextrous to pick locks and pockets such. You can give clerics wisdom as the other big mental ability, though there are plenty of anchorites and mystics who ought to have plenty of spiritual power but little common sense. Druids are kind of a type of cleric, so that fits as well. Warlocks have whatever ability they need to channel their powers. But then it starts getting complicated. The monk has been around forever so people want to play martial artists (and a significant subset of geeks like martial arts because they build self-confidence and physical ability without having to play team sports, not to mention having exotic origins and being associated with interesting philosophies), but they really need strength, dexterity, and some constitution. Similarly, the paladin as a fighter/cleric has split abilities too. Same for the ranger as a fighter/druid. The barbarian...well, that's a fighter with an anger problem. Maybe it's constitution because you need a place to put that somewhere?
I actually studied (informally) a bit of Hermetic stuff as research for a never-written fantasy novel, and sometimes the correspondences lined up pretty cleanly (fire, iron, red, Mars, war) and sometimes they had a list of things and you could see they were just trying to fill out colors, elements, etc. (Green is copper because of the patina on copper...fine, but then blue is associated with tin and Jupiter why? Wouldn't purple, the royal color, make more sense? The main ore of tin, cassiterite, is black, but you already used that for lead, which actually looks more bluish as a metal... why isn't copper red, the metal itself is, oh wait you took that for iron.) You have a similar problem with the Chinese elements, though there they had a system of relationships they were trying to fill out too--I can get that water puts out fire and gives rise to wood, but the bit about dew collecting on metal in the morning strikes me as an obvious bit of Procrustes.
You wind up getting the same sort of effect when you try to tie each class to an ability score. OK, wizards are smart and fighters are strong since 1974. Bards really should be charismatic and rogues dextrous to pick locks and pockets such. You can give clerics wisdom as the other big mental ability, though there are plenty of anchorites and mystics who ought to have plenty of spiritual power but little common sense. Druids are kind of a type of cleric, so that fits as well. Warlocks have whatever ability they need to channel their powers. But then it starts getting complicated. The monk has been around forever so people want to play martial artists (and a significant subset of geeks like martial arts because they build self-confidence and physical ability without having to play team sports, not to mention having exotic origins and being associated with interesting philosophies), but they really need strength, dexterity, and some constitution. Similarly, the paladin as a fighter/cleric has split abilities too. Same for the ranger as a fighter/druid. The barbarian...well, that's a fighter with an anger problem. Maybe it's constitution because you need a place to put that somewhere?