Why are ability scores and ability modifiers separate?

[Elves]

Seems significantly easier if it were just "your Strength score is +10", "your Dex score is -2".

Is the minor amount of articulation gained by +1 bonuses worth doubling the complexity of the game's second most basic mechanic?

[Morty]

As far as I can tell, 3E tried to introduce a consistent progression for attributes, while keeping to the 3-18 range older editions had. So we got this mess. There's no good reason for it, certainly, but it's unlikely to go anywhere.

[Batcathat]

Have you checked out this thread? I think it touches on a lot of the same questions.

[Mastikator]

It's a sacred cow. The only value it provides is that players from old editions don't have to learn new stuff.

[Yora]

It comes from the time when ability scores in D&D were rolled on 3d6. Which gets you a number from 3 to 18.

That number was used for attribute rolls by rolling 1d20 under your attribute score. If your Strength is 14, you need to roll 14 or lower on a d20 to do a generic Strength task that has no specific rolls. If your Constitution is 8, you need to roll 8 or lower to do a generic Constitution task, like running for a long time or something like that. It wasn't considered necessary to have specific difficulties for such tasks.

"It used to have a purpose 40 years ago" is the reason behind most useless things in D&D.

[MoiMagnus]

Far from the first time this discussion happens. Here are some arguments I remember seeing:

Against the separation:
(1) Removing ability scores and keeping only modifiers works well. (See for example Mutant and Mastermind 3e, but that's not the only D&D derivative that made this choice)
(2) Having two redundant values is an unnecessary complexity, and can be confusing to new players.
(3) Some peoples like to have numbers centred around 0 as defaults.

For the separation:
(1) Effects that damage ability scores works better with the granularity of scores than modifiers. Moreover, it's more natural to have 0 as "you are dead if you reach this level" than -5. In general, this additional granularity can be used for some effects (prerequisites for multiclassing are odd, etc)
(2) The rolling methods is much more natural with ability score. Take "4d6, best 3, subtract 10, divide by 2" is quite awkward, and other rolling methods give other statistical repartitions. In general, rolling odd score VS even scores has some interesting interaction with half-feats.
(3) Tradition. D&D is not a new game, even if this separation had no place in a new game, it still has a place in D&D. Changing something needs a good reason.
(4) Some peoples don't like negative numbers, and prefer numbers centred around 10. Additionally, the scale of ability score closely match the range of a d20, which is nice.

[truemane]

Metamagic Mod: we have another active thread discussing this exact topic already.