The term "invocation" smacks of "real magick" to many people. It is however a term which seems to be used loosely by many of the authors in the past and is somewhat difficult to define. In the modern practice of magick invocation means the contacting and experiencing directly of a particular willed force by allowing, calling or inviting that entity to come to be experienced within the consciousness of the practitioner. It can vary from being a vague visionary experience to being a full possession by a specific god or goddess.
One type of invocation that is often used in a ceremonial magick setting is that of "taking on a godform". This consists of standing in the characteristic posture of a given god and strongly imagining the outward appearance of the god surrounding oneself. This is a powerful way to change consciousness and to allow particular characteristics that are associated with the chosen god to manifest.
The type of "thing" that is invoked is usually chosen in order to be in keeping with the purpose of a ritual (for instance the goddess Venus may be chosen for a ritual designed to improve ones feelings of love). Sometimes things are invoked about which the practitioner knows very little. The purpose of this is usually to gain information.