Evocation
From Breaking Worlds
Evocation is the magical art of summoning, appeasing, and binding spirits. A person who treats with the spirits to worship and gain enlightenment is generally called a priest, while a practitioner who uses them to gain more immediate power is called a witch - though the distinction is often blurred.
Summoning and binding
Evokers are capable of calling spirits from the Spirit World into the mortal plane by performing a ritual. The more powerful the spirit is, the more powerful the ritual must be; a spirit of the least degree can be summoned fairly easily, while a greater spirit requires an elaborate performance and usually a substantial sacrifice.
It is possible to perform a summoning ritual without a specific spirit in mind. An evoker can perform a ritual to call a spirit of a particular element and degree, or an ancestor matching a broad description. Where possible, however, it is best to call a spirit by name; temples, scholarly institutions, and similar organisations sometimes record the names of significant spirits for this reason.