Ability damage doesn't actually reduce the ability score. You don't recalculate all of the various statistics based on the adjusted score (e.g., carry limit for Strength, maximum HP for Constitution, bonus spells and maximum spell level for caster stats). You simply apply a penalty of -1 per 2 points of ability damage to all checks that involve the damaged ability score.
Ability drain actually does reduce the score, so you immediately recalculate everything based on the new score.
For example, if your Str 17 cavalier in full plate mail carrying a greatsword takes 16 points of Strength damage, they won't be much good in a fight, but they can still move and walk just fine. If they took 16 points of Strength drain, though, they're essentially immobilized until someone helps them out of their armor (as they're over five times their carry limit).
Edit: citation
So it's checks ONLY that take the -1 penalty per two points? The SRD states that damage to CON reduces HP as well so there is no difference between CON damage and drain, correct?
There are still some functional differences: Ability damage heals on its own, drain doesn't. Ability damage doesn't prevent feats from working -- drain does... so if you have a feat that has a Con score prerequisite then damage won't cause you to lose the feat while drain will.
So it's checks ONLY that take the -1 penalty per two points? The SRD states that damage to CON reduces HP as well so there is no difference between CON damage and drain, correct?
You are correct that for particular stats, you still do a few specific things like HP. (Should have read up a little more.) But they still aren't the same. Damage to Int, for example, still doesn't reduce your spellcasting capabilities, just the spell DCs. As Abraham spalding mentioned, you don't lose access to feats for taking ability damage. Con damage also does not change your death threshold, which is defined as negative hit points equal to your Con score (which is unaltered by damage).
Thanks so much for your feedback guys. These rules are so poorly described in the SRDs and core rule book that I'll run all this by my PFS peeps. Your feedback does help though.
Yum... I find them very clear -- but it could be you aren't looking in the right place: Here are the rules.
Of course it could be I'm just more use to reading the psuedo-code that is role-playing rule sets too...
What I'm getting out of this is that damage affects the the ability modifier, and drain the ability score. Is that an accurate way to look at it, or are there exceptions to that as well?
What I'm getting out of this is that damage affects the the ability modifier, and drain the ability score. Is that an accurate way to look at it, or are there exceptions to that as well?
Mostly, but read the linked rules, as there are a few things damage still modifies--much to my own consternation, as it makes the game more complicated.
so if you have a feat that has a Con score prerequisite then damage won't cause you to lose the feat while drain will.
Just a clarification here... you don't actually lose the feat, you just can't use it until the ability drain has been healed.
From the Feat Prerequisites rules:
A character can't use a feat if he loses a prerequisite, but he does not lose the feat itself. If, at a later time, he regains the lost prerequisite, he immediately regains full use of the feat that prerequisite enables.
I read your citation. Looks like damage doesn't affect class features relying on ability mods (such as rounds of rage), and bonus spells. What else?
so if you have a feat that has a Con score prerequisite then damage won't cause you to lose the feat while drain will.Just a clarification here... you don't actually lose the feat, you just can't use it until the ability drain has been healed.
From the Feat Prerequisites rules:
A character can't use a feat if he loses a prerequisite, but he does not lose the feat itself. If, at a later time, he regains the lost prerequisite, he immediately regains full use of the feat that prerequisite enables.
You are quite correct -- thank you for the clarification on the point, I should have been more precise in my language.
How would the difference between drain and damage be represented in game? (RP)