Magic

Magic is the ability possessed by some individuals to manipulate the ambient energies of the world to produce desired results. In Realms, magic is commonly referred to as "the Art".

The goddess Mystra controls the Weave which is what powers the magical energies of Abeir-Toril. The goddess Shar has control of the Shadow Weave which flows in-between the normal weave and enables the use of Shadow Magic.

The History
Lord Ao created the universe. At first it was nothing but energy, with neither light nor dark, heat nor cold. Eventually the energy created two deities - Selune and Shar. Together they created heavens and Chauntea, the embodiment of the world of Toril. Chauntea begged for light and warmth so that she could create life on the new world, but Shar opposed this vehemently. The consequent war between the sisters created new deities – war, murder, and destruction being among them. When Selune lit one of the nearby heavenly bodies on fire to provide the light and warmth needed, Shar became enraged, trying to extinguish light everywhere. Selune tore the energy from her own body and flung it at Shar, where it joined with Shar’s energy and passed from both of them, thus creating the goddess of magic, Mystryl. The birth of Mystryl not only brought a truce to Selune and Shar, but created the Weave. In the newly created Toril, magic abounded in everything, but in its raw state, it was too dangerous for mortals to use. The weave is a like a fabric, consisting of many threads, all woven together to create an intricate design. Spellcasting and the use of magic items pulls individual threads and reweaves them, creating a new design. Now both mortals and deities could use magic through this fabric that was both the embodiment of Mystryl and a conduit to raw magic.

When the Phaerimm, a race dwelling under the surface of the earth, began to cast spells draining the empire of Netheril of its magic, a powerful mage named Karsus created a link to Mystryl in an attempt to steal her power, become a god and save his empire. This caused a great rift in the Weave, and Mystryl was so weakened that she sacrificed herself to save the world. Since she was the Weave, magic immediately ceased all across Toril. A new godess of magic named Mystra was born, and she was able to repair the weave in a way that such powerful spells could never be used against it again.

The Art
Any magic that doesn't originate from a deity is defined as arcane magic. (Note, while all magic is accessed through the Weave, which is maintained by a deity, this does not make all magic divine magic.). The use of arcane magic is refered to as the Art, in day to day speech, and a vide variety of people (and character classes) are able to practice the Art, to a smaller or larger extent, though the way in which the access the Weave can differ dramatically. Most wizards spend long years researching their art, gathering spells to their personal book, and each day they can only memorise a small fraction of these, the memory of the spell being wiped from their mind as it is cast. The wizard has to re-study the spell before he or she can cast it again, unless more than one casting of the spell in question was prepared. Sorcerers, also known as innanoths (for their innate mastery of the weave) are not required to research spells, they tap the Weave in a more direct manner, but because of this the selection of spells available is all the more limmited to a Sorcerer than a wizard. Bards, Assassins and many other prestige classes access the weave in some way as well to use certain magical abilities, practicioners of the Art all, wether or not they would acknowledge such kinship with each other.

The Power
Magic that originates from a spell-granting deity, usually through prayer, is divine in nature and is called the Power by the common folk. Clerics, druids, paladins, rangers and many prestige classes all derive their spell and spell-like abilities from a deity. A practicioner of the Power has no affinity with the Art, as their spells are planted in their minds directly by their patron deity, and they do not tap the Weave. Casting divine spells is more like an exclamation of faith that brings about a sensation appropriate to the patron deity who the faith was devoted.