Volume II of 'An Introduction to the Great Art', penned by Bel'qualyn Do'neld for zhaunin of Sorcere in great Udos Dro'xun.
With an understanding of the Planes, however limited, the student can begin to comprehend the nature of the Art. The Planes have different natures and many connections, manifesting as lines of Power throughout the multiverse. The Art is the manipulation of Power through incantation or will, allowing the practitioner to manipulate the Planes themselves. The lesser Arts, facets of the Great Art, specialise in different aspects of this manipulation.
The Art of Conjuration is the Art of forging a connection between one or more of the other Planes and the Prime Material, and using this connection to draw something of the other Plane back to the Material - a creature, object, or substance. An example is the drawing of a demonic imp from the Abyss to the Prime Material.
The Art of Evocation is the Art of touching another plane and releasing the energies of that plane into this one. The connection is made and broken through the incantation, and it is only power that passes between. An example is the touching of the Elemental Plane of Fire to create a fireball.
The Art of Necromancy is the study of the Negative Plane. Closely related to both the Arts of Evocation and Conjuration, a necromancer focuses solely on the Negative Plane, practicing conjuration and evocation in the specific context of the single Plane. Necromancy is an Art in and of itself both because of the unique effects of the Negative plane on living creatures of the Prime Material, and due to the sheer body of research that has been done in this area. The essence of the Negative Plane is decay, and thus this is also the essence of the Necromantic Art.
The Art of Transmutation is the Art of manipulating objects or beings in the Prime Material, and substituting parts of their elemental makeup. For instance, the spell Petrify involves replacing the Water in the target with Earth.
The Art of Enchantment is the Art of manipulating objects or beings in the Prime Material, and altering the pattern of their elemental makeup. To demonstrate the concept, one could take three pebbles and line them in a row. An enchantment might change the order of the row; there is no change to the materials comprising the row, but it is no longer the same row.
Enchantments, however, fade with time as the natural order of the object reasserts itself. This natural order is best envisioned as the imprint an object makes in the Weave of Power. The Art of Divination is the Art of reading these patterns and understanding their relationships; thus a diviner might, from the hair of another, be able to see their face.
The Art of Illusion is closely tied to the Plane of Shadow. The Shadow Plane is a pale imitation of our own, the imprint of its objects in the Weave weaker and thus more easily manipulated. A practitioner of the Art can ward themselves in Shadow for defense, or bring creations of shadow into this realm and shape them to his will.
Finally, the Art of Abjuration is the Art of wards, of constructs of power that form connections to other Planes and take energies unleashed in this Plane and channel them elsewhere. Just as a shield deflects a blow to one side, so a ward deflects energy from the Prime Material to another Plane.