Do Prestige class levels stack with caster level?

Question

Do levels taken in a prestige class of the same kind of magic (arcane/divine) as a base class stack with a character's existing caster level? For example, if a Wizard 4/Rogue 3/Arcane Trickster 2 character levels up and takes another level of Wizard (becoming W5/R3/AT2), do they qualify for the Forge Ring bonus feat (requires caster level 7)?

The rules seem to say both yes and no. Under the definition of caster level:

A spell's power often depends on its caster level, which for most spellcasting characters is equal to her class level in the class she's using to cast the spell.

But Arcane Trickster says:

When a new arcane trickster level is gained, the character gains new spells per day as if she had also gained a level in a spellcasting class she belonged to before adding the prestige class. She does not, however, gain other benefits a character of that class would have gained, except for additional spells per day, spells known (if she is a spontaneous spellcaster), and an increased effective level of spellcasting. If a character had more than one spellcasting class before becoming an arcane trickster, she must decide to which class she adds the new level for purposes of determining spells per day.

Furthermore, if a character has multiple spellcaster base classes of the same type of magic, do all levels from these classes stack, does their highest base class combine with their prestige class levels, or do they just use the highest level base class? e.g. what would be the caster level of a Wizard 5/Sorcerer 3/Loremaster 2 character?

Answer 1

Yes, they stack like the rule you cite says, if the specific class says they do. This is an example of exception-based design - the general rule is "only the one class counts" but then the specific rules in the other classes can say "but I do."

Not all prestige classes are alike so you should carefully read their Spellcasting benefit. In this case, Arcane Trickster says "I stack."

But classes that do not say that phrase, like Wizard and Sorcerer, do not stack. In your second example, Loremaster's spellcasting is worded like Arcane Trickster (as if she had gained a level in a spellcasting class she belonged to...), and you would need to decide whether you want it to stack onto your 5th level wizard spellcasting or your completely separate 3rd level sorcerer spellcasting. Assuming the former, you'd cast your spells from wizard slots at level 8 and your ones from your sorcerer slots at level 3.

It's kinda obvious why this is, the core idea behind prestige class design is "continue what you were doing, down a slightly weirder path" and therefore completely penalizing a spellcaster by e.g. halving their spellcaster abilities would be undesirable (even at that, many don't add a spellcasting level at every level and have one or two "penalty" levels.

Answer 2

My general trick for remembering how prestige classes work with casters is that base classes (key word being base) are kept separate even if they are the same type (arcane, divine, psionic). Prestige classes can add spells or powers to existing base classes. Sometimes they do not, you can tell the difference by looking at what they grant that level, on the far right side of the table is should have a column for spells (Spells per day).

If it says something like +1 level of existing class, then you gain spells as if that base class had leveled up (but none of the bonus saves, BAB or other class abilities). If it has numbers in that column (such as it does for the prestige class Assassin), then you gain a new list of spells with its own limit of how many spells per day you can cast. it has its own caster level for those spells. when they do add levels you have to select which base class they add to (the time you choose which one they add to is determined either at the time you enter the prestige class or the time you gain the spells per day.

Answer 3

It strongly depends on the prestige class itself. There are several "types" of prestige classes and their approaches to caster level advancement:

• Full progression classes, which means every level You get spells known, spells per day and caster level as if You have leveled in respective spellcasting base class.

• Partial progression classes, which means You get spells known, spells per day and caster level as if You have leveled in respective spellcasting base class BUT ONLY ON SPECIFIED LEVELS. So for example every second level of the prestige classes.

• No progression prestige classes. Those are classes that trade spellcasting progression for something else related to Your spellcasting ability, for example free metamagics, ability to switch spells on the fly, etc.

• D&D 3.0 also had another type. Those were classes that progressed for example only spells per day and spells known but not caster level. I'm quite sure none of such classes exist anymore though, as they were all updated in 3.5 and PF to work the same way (so either You get progression or not, but You can't get only some parts of the progression).

To sum things up, in Your very example of Wizard 5/ Sorcerer 3/ Loremaster 2, You will have a Caster Level of 7 in Wizard class or Caster Level of 5 in Sorcerer class. Mind that even though both those classes are arcane, they progress separately, so when You level up as prestige class You need to choose which of Your spellcasting classes casting ability does progress.

There are also so called "multiple progression" prestige classes such as Mystic Theurge (which is awesome in Pathfinder) but those are very rare cases and such progression is mentioned in class itself and in most cases is what such class is all about.