Does stat drain/damage make you lose bonus spell slots?

Question

My character is a 7th level Magus with 18 Int after items, therefore receiving an extra 1st, 2nd, 3rd, and 4th spell, in addition to the base Magus spells, even though he can't cast the 4th yet. If he were to take 4 points of Intelligence drain/damage, would he lose the extra 3rd and 4th spell slots? Or are those retained based on your base casting stat?

Answer 1

Ability damage, for the sake of simplifying the rules, do not make you recalculate any of your other abilities that depend on the ability damaged.

While ability drain does, making you lose access to your bonus spell slots, but not your base slots gained from your class.

This is what James Jacobs (Paizo's Creative Director) wrote oficially about this (original post on the rules forum):

I am confused on the different types of Ability Damage, Drain, and Penalty. Plus some spells like Ray of Enfeeblement and Touch of Idiocy seem to even have special rules. How do these effects really work? (James Jacobs 4/23/10) Ability damage only results in a penalty to actions associated with that ability score; it does NOT make you lose access to feats or spells that require ability score minimums, since your actual ability score does not lower. Only ability DRAIN can make you lose access to spells you can cast or feats that have prerequisites.

But it's not that simple. Some effects that cause ability damage or ability penalties DO have additional effects. Touch of idiocy is one such spell, since it says in the spell's description that it affects the target's ability to cast some or all of its spells if the penalty imparted to the ability score drops low enough. This is an exception to the general rule for ability scores and applies only to touch of idiocy (the point of the spell, really, is to be a lesser version of feeblemind that screws over spellcasters, after all).

Ray of enfeeblement, on the other hand, does NOT have this type of language. It merely works as a normal penalty to an ability score.

1. A 12th-level wizard with a 16 Intelligence takes a 3 point Intelligence penalty from Touch of Idiocy. What is the highest level spell he can cast, sixth or third?

   Third.

2. A 12th-level wizard with a 16 Intelligence takes 3 points of Intelligence damage. What is the highest level spell he can cast, sixth or third?

   Sixth.

3. A 12th-level wizard with a 16 Intelligence takes 3 points of Intelligence drain. What is the highest level spell he can cast, sixth or third?

   Third.

4. A fighter with 13 strength and the Power Attack feat takes a 3 point Strength penalty from Ray of Enfeeblement. Can he Power Attack?

   Yes.

5. A fighter with 13 strength and the Power Attack feat takes 3 points of Strength Damage. Can he Power Attack?

   Yes.

6. A fighter with 13 strength and the Power Attack feat takes 3 points of Strength Drain. Can he Power Attack?

   No.

Answer 2

Ability score damage doesn't cause spell loss…

Ability score damage, in part, says

This damage does not actually reduce an ability, but it does apply a penalty to the skills and statistics that are based on that ability.

So each 2 points of ability score damage to a creature's Intelligence score causes the creature to suffer a −1 penalty on skill checks with any skill having Intelligence as its key ability and a −1 penalty on the creature's saving throw DCs for effects that base their saving throw DCs on the creature's Intelligence (like a typical wizard's spells). No other effects (like a modification of the bonus spell slots) occur until the ability score damage equals the creature's Intelligence score—at which point the creature becomes comatose.

This is a significant change from Pathfinder's antecedent D&D 3.5e so as to speed play. Also note that while there's a D&D 3.5e condition comatose, comatose exists broadly in Pathfinder only as an optional byproduct of disease and poison; however, the term crops up in other places like in the description of the spell eyebite.

…But ability score drain means recomputing everything

Ability drain, in part, says

Ability drain actually reduces the relevant ability score. Modify all skills and statistics related to that ability. This might cause you to lose skill points, hit points, and other bonuses.

These "other bonuses" include bonus spells for a high Intelligence score. In other words, imagine ability drain as if the character had the new, post-drain ability score his entire career and recompute on the character's character sheet everything that's affected by the new score.

Likely because ability drain is much rarer, ability drain isn't as precise as ability damage as to how to determine its impact—ability drain doesn't explain, for example, how to prioritize the skills from which a creature should subtract its lost skill ranks—, and leaves details up to the GM. Also, whether ability drain can cause the immediate loss of prepared spells—and, if so, which spells—is unmentioned; ask the GM.