Rules Question

[Yogibear41]

Say I am a 6th level character with 5 levels of cleric and 1 level of wizard, I take Alternative Source spell as my 6th level feat, I then take levels of Incantatrix because I can prepare my cleric spells as 3rd level arcane spells, can I apply Incantatrix casting advancement to my cleric class or do I have to apply it to my Wizard casting?

[Venger]

Say I am a 6th level character with 5 levels of cleric and 1 level of wizard, I take Alternative Source spell as my 6th level feat, I then take levels of Incantatrix because I can prepare my cleric spells as 3rd level arcane spells, can I apply Incantatrix casting advancement to my cleric class or do I have to apply it to my Wizard casting?

incantatrix actually doesn't discriminate, so you can assign it to whatever you want. assign it to your cleric half, and have fun.

[Yogibear41]

"When a new incantatrix level is
gained, the character gains new spells per day (and spells known,
if applicable) as if she had also gained a level in whatever arcane
spellcasting class granted her access to 3rd-level spells before
she added the prestige class."

From Player's guide to Faerun, which is the 3.5 update and most recent version if I am correct. So it kind of dose care? Hence my Question.

[Venger]

"When a new incantatrix level is
gained, the character gains new spells per day (and spells known,
if applicable) as if she had also gained a level in whatever arcane
spellcasting class granted her access to 3rd-level spells before
she added the prestige class."

From Player's guide to Faerun, which is the 3.5 update and most recent version if I am correct. So it kind of dose care? Hence my Question.

That's what I get for looking at the magic of faerun version. I thought that was the 3.5 one. Yes, your reading is correct. pgtf's incantatrix does require you to progress your wizard half, since it's an arcane class and cleric, even with alternative spell source, which lets you cast arcane spells, doesn't make it an arcane class.

[Firest Kathon]

In my understanding Incantatrix does not progress Wizard either.


whatever arcane spellcasting class granted her access to 3rd-level spells

Since the arcane spells are provided by the cleric class, as per Alternate Source Spell, you cannot progress your wizard (does not grant 3rd-level spells) nor your cleric (not an arcane spellcasting class) side.