For purposes of the Erudite, what constitutes a Psionic class for PrCs?

Question

The Erudite has the following exception posted in its class description:

Exception: If a character with erudite levels gains at least as many levels in another psionic class as he has in his erudite class, he permanently loses the ability to add additional powers (above and beyond the two gained at each new erudite level) to his repertoire of powers known.

So, if I'm a Spell to Power Erudite for example and I decide to take The Metamind PrC at level 5 (ignoring the fact that that's a bad choice for the loss of the bonus feat) so I can sequester any powers or spells I don't care about and then level to character level 10, suddenly I can't progress in my main casting class period.

What exactly defines a class as "Psionic" vs "Arcane" per the RAW?

Either I'm blind to the parts that make it clear to me or there's not a clear statement that covers it and it's meant to be taken as "classes that involve Psionic powers, abilities or class features in some way."

The point of asking this is essentially to build up a line of reasoning to give to the DM for a house rule. I'd be fine with it if it said other manifesting classes, or something along those lines that refers to classes that explicitly give you the ability to manifest powers, which PrCs usually don't.

Answer 1

Expanded Psionics Handbook does introduce Chapter Two: Classes with

The Classes

The four psionic classes, in in the order they’re presented in this chapter, are as follows.

• Psion: [...]
• Psychic Warrior: [...]
• Soulknife: [...]
• Wilder: [...]

Complete Psionic establishes that these four are “not the only psionic classes the game could feature,” but then neglects to say that the classes it presents are actually psionic classes—though “new character classes for psionic characters” maybe gets close.

So by the very strictest of RAW, the only “psionic classes” are psion, psychic warrior, soulknife, and wilder; those are the only classes that are explicitly labeled as such by an official publication.

Expanded Psionics Handbook does refer to the prestige classes in that book as “psionic prestige classes,” though it’s unclear if that counts as a “psionic class.” Likewise, precisely what erudite means in that quotation is also underdefined, and we can’t really know precisely what does or doesn’t count.

Which is precisely the situation than we have for arcane or divine, which are not defined at all. The fact that we know explicitly that psion, psychic warrior, soulknife, and wilder are psionic classes is actually an improvement over the arcane or divine side, but it’s probably not a good enough answer for handling the erudite. For that, you’ll have to ask your DM.

Personally, my ruling is that the “Exception” rule for the erudite is dumb, and should be ignored. The erudite is a variant class presented at the back of a poorly-written book, and has a lot of problems. Including it in the game necessitates some DM oversight and adaptation—part of that should be ignoring that rules, as it is a bad one. So you’ve got that going for you. On top of that, it seems to me that even if you include that rule, levels that progress erudite manifesting should count towards your erudite class level for it. So that would be in your favor, too.

All that said,

Unfortunately, I cannot more strongly recommend to any and all DMs that spell-to-power erudite needs to be banned. That option is flat-out broken, and it makes the erudite far-and-away the strongest class in the game. It is not a good addition to any game.

If you want magic spells using psionic-like mechanics, I strongly recommend Ernir’s Translation of Vancian Spellcasting to Psionic Mechanics. If you want to mix magic and psionics, play a cerebremancer—try my rework of the class if the Expanded Psionics Handbook is too much of a trap for you. But don’t play spell-to-power erudite. It is just going to break the game.