Invocation is also known as theurgy or goety.
Invocation is the practice of invoking spirits and persuading them to do one's bidding. Anyone can practice invocation, if he or she knows the proper rituals, but those with sorcery in their blood excel at it.
Invocation calls upon the entities of the unseen world, and like them, its consequences are invisible but highly signficant.
There are three main classifications of the practice of invoking spirits.
Goeticans resemble sorcerers, and most sorcerers who practice invocation tend to do so as goeticans. Their motive is personal gain, whether material or spiritual, and their goal is to command spirits.
Priestly prayer and rituals, are, in practice, invocations, though unlike conjurers they deal with a hierarchy of spirits, and, after a fashion, form part of that hierarchy. Priests are reluctant to admit that there is any resemblance between their prayers and rituals on one hand, and other rituals on the other, but often do not make the same distinction for rival faiths.
Shamen form a middle ground between priests and conjurers, being less hierarchical and single-minded than priests, and more spiritual and community oriented than sorcerers.