The Pact System (2003)

From Introduction:

The pact rules grant added flexibility to spellcasters. For a wizard, they allow her to prepare a spell that she can use in a variety of ways, making her somewhat like a sorcerer. For a sorcerer, they allow him to go beyond the confined list of spells known. For both classes this added flexibility incurs costs. One cost is the need to dedicate slots to Pact Gate spells. For wizards this cost is somewhat minor. Sorcerers effectively “pay” more for the slot since they have so few to begin with, but they also gain more since added flexibility means so much to them. The most significant cost for both classes is that of joining a pact and developing the skills and abilities to use the pact. This cost takes a variety of forms. For some pacts you need a high skill; others require special commitments; others require sacrifices in the form of oaths and taboos; almost all require an expenditure of some kind of resource (influence or gold).