During our last session, my character took 12 negative levels, and is a multiclass character with 8 sorcerer levels. He has sufficient HD and HP to survive gaining those negative levels so now the question is what does "level dependent variables' really mean in this context, and how does it effect his spell casting. I've seen lots of posts debating it but most threads are pretty old. So rather then resurrect a zombie thread, I figured I ask again.
1) Does he have an effective CL of -4? 0? or 1?
This is a question of what is the floor for CL. Can it be 0, negative or is the minimum 1.
2) Can he cast any spells at all.
In the CL description it states:
You can cast a spell at a lower caster level than normal, but the caster level you choose must be high enough for you to cast the spell in question,
So does that mean that even though you retain the spell slots, you're unable to cast them because your CL is reduced by 12?
3) If you have an ability that grants you a +effective caster level, how do they interact with the negative level effects.
You don't lose caster levels from negative levels (read the passage about negative levels carefully). Only the spell variables are treated as if you were lower.
Example: a sorcerer 12 with 7 negative levels can still cast his Cone of Cold, but he would be reduced to doing 5d6 damage.
Since the variables include damage, number of targets and range, this does hamper spellcasting a lot, but several spells are no affected at all, since they have none (like Stone to Flesh..OK, the range would suffer).
It is probably up to your DM to decide what happens regarding the 0/-4 thing. I would go with the 0 option as DM, since you cannot take more away than there was in the first place (your fireballs would do 0d6 damage, not -4d6).
Since you don't lose CL, question 2&3 don't matter.