Instead of specializing in a focused arcane school of magic, a wizard can choose to specialize in one of the four elemental schools of magic. Like a normal arcane school, an elemental school grants a number of school powers and one bonus spell slot of each level the wizard can cast, from 1st on up. This bonus spell slot must be used to prepare a spell from the elemental school’s spell list. Unlike a normal arcane school, each elemental school requires the wizard to select his opposed element as his opposition school (Air opposes earth, fire opposes water). He does not need to select a second opposition school. He must expend two spell slots to prepare a spell from his opposed elemental school as normal.
Advanced Player’s Guide. Copyright 2010, Paizo Publishing, LLC; Author: Jason Bulmahn.