This archetype prevents a spellcaster or manifester from utilizing several forbidden schools or disciplines. Whether by choice or the demands of others, these characters must learn how to do more with less - or simply specialize within a narrow focus to remain effective. For example, necomancy is banned in the Floating Cities just as psychokinesis is denied in the Industrial Kingdoms.
This goes further than a wizard's opposing schools and outright prevents the learning or casting of spells (and similarly for powers). In practice, a spellcaster or manifester has access to about half as many spells or powers as a character of the base class normally would. This effectively reduces a class's tier by 0.5 (moves your class half a tier lower).
At character creation, choose 4 classic schools or 3 classic disciplines. These are your forbidden schools or disciplines. At least one of the schools must be Transmutation or Conjuration, and you can't choose Divination. At least one of your disciplines must be Metacreativity or Psychometabolism, and you can't choose Clairsentience. You can't learn, cast, or manifest spells or powers from these schools or disciplines. Not even from domains, knowstones, or methods of automatic spell/power retrieval. Any spell-like or supernatural abilities function normally, as do spell-trigger/completion items such as wands or scrolls (you may need to make Use Magic Device checks for spells no longer on your list, however).
This effectively blocks any attempts to use these forbidden abilities. If a character finds a workaround, such as 100% real shadow-evocations or summoned spellcasters with access to forbidden spells, then this archetype may not necessarily continue to reduce the tier of the base class. Similarly, forbidden subschools or subdisciplines are possible, but subject to GM approval on a case-by-case basis (in general, half or more of all spells/powers must be forbidden).
For example, a sorcerer might select conjuration, necromancy, evocation, and enchantment as her forbidden schools. She can't learn or cast spells of these schools, not even through those provided by her bloodline. She can still learn and cast transmutation, illusion, divination, and abjuration spells normally. Forbidden spells can still be accessed through wands, scrolls, or other items with a use magic device check.
This archetype modifies the Spells, Powers, Domains, Spontaneous Casting, Arcane Schools, and similar class features of the base class. It is still combatible with other archetypes which modify spellcasting or manifesting, so long as those archetypes do not explicitly depend upon spells or powers from a forbidden school or discipline.