[House Rules] AD&D Ability Scores

I am taking a break from my Adventures in Fantasy posts to do this real quick.

Note: The following better suits the detailed approach of AD&D instead of the looser approach of D&D.

I like to tinker with the rules of the various games I play.  The game I have probably house ruled more than any other is AD&D.  I have always wanted to look into expanding the list of abilities but I have never given it a serious effort.  I think it could work.  I honestly do not know if it would be worth the effort but I think it might be worth a look.  Since there are 3 physical and 3 mental abilities with a total of 6 abilities I would want to maintain the same sort of balance when adding the new abilities. I would suggest adding 2 abilities to the core six of Strength, Constitution, Dexterity, Intelligence, Wisdom, and Charisma.

Agility (AGL): Agility would represent something like total body control and also set the modifier for AC.  This would mean Dexterity now represents hand to eye coordination and actions requiring fine manipulation.  Some of the thief skills would now be affected by Agility and some by Dexterity.

Composure (COM): Composure would represent something like mental endurance, coping with stress, and the ability to persevere in the face of terror; similar to Sanity from Call of Cthulhu.

I'm sure that both of these abilities could be added and put to good use.  Composure could be fun to mess with but it could also be done with a saving throw.  I have always thought there should be a split between Dexterity and Agility. I'm not quite so sure it would be worth the effort.  Honestly, I would not want to worry about figuring one or more additional ability scores when using an "official" module or resource.  This is just one of those ideas that cross my mind from time to time but I have never acted upon it.  Maybe one of these days I will.  On the other hand, in my older age with limited free time I would rather play than try to decipher a bunch of unnecessary house rules.  Not that I am opposed to house rules - I plan on sharing some of mine in this blog - but let's use them where they are needed.

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edit 1 - fat fingers.
edit 2 - fixed some awkward wording.