Magic

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

The goddess Mystra controlled the Weave which was the main medium for channeling the arcane energies of Abeir-Toril. The goddess Shar controlled the Shadow Weave which flows in-between the normal weave and enables the use of Shadow Magic.

Divine magic was drawn from specific deities, or from nature itself and is not influenced by either Mystra or Shar as evidenced by the fact it continued to work when arcane magic ceased to function. Historically this made it the most reliable form of magic.

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 – Selûne 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 subsequent war between the sisters created new deities – war, murder, and destruction among them. When Selûne lit one of the nearby heavenly bodies on fire to provide the light and warmth needed, Shar became enraged, trying to extinguish light everywhere. Selûne 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 Selûne 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 goddess 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.

Divine magic
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 spells and spell-like abilities from a deity. A practitioner 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 to whom the faith was devoted.

Faith magic
A small subcategory of divine spells could make use of the "devotional energy" that came from many worshipers congregated in a specific location dedicated or sacred to a deity. Once a focus was created to harness this energy, it could be used for protection, improving harvests, controlling weather, improving communication between diverse peoples, and improving public health.

Arcane magic
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 referred to in day-to-day speech as the Art, and a wide variety of people (and character classes) are able to practice the Art to a smaller or larger extent, though the way in which they 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 memorize a small fraction of these. The memory of the spell is wiped from his or her 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 to a sorcerer is more limited than that available to a wizard. Bards, assassins and many other prestige classes access the Weave to use certain magical abilities.

Schools
Schools of magic are categories of spells organized by general function. Spells are created by wizards with these schools in mind, though divine spells fall within these preset categories as well. Still, there are also some of spells that defy categorization within a school. Some spellcasters (mostly wizards) choose to specialize in spells from a certain school; they focus more effort into these spells than any other, but at the expense of all spells from one or more other schools. These schools of magic have been in existence for longer than anyone cares to remember and no one seems to know who originally came up with them. They also show no signs of being abandoned.

Most schools of magic also have subschools that help define the spells with even more accuracy. The major schools of magic are as follows:
 * Abjuration : Spells of protection.
 * Alteration : Spells that can transform the nature of the physical world or objects in it.
 * Conjuration : Spells that create or transport people, energy or objects.
 * Divination : Spells that allow the caster to see things that they normally wouldn't be able to.
 * Enchantment : Spells that affect the minds of other creatures.
 * Evocation/Invocation : Spells that create energy out of the raw power of the Weave.
 * Illusion : Spells to fool the senses.
 * Necromancy : Spells that deal with positive energy, negative energy, and both the living and the dead.

Casting
Verbal component
 * Many spells require the caster to speak certain words, or, in the case of a bard, create music, to cast a spell. Being prevented from speaking, such as a gag, or effects that remove sounds, such as certain magical effects, makes it impossible for a caster to cast such a spell. A deafened caster may fail when casting a spell, by misspeaking, which causes the spell to be lost.

Somatic component
 * Many spells require the caster to make a motion to cast the spell. If the caster is unable to make the correct motion, the spell cannot be cast. Wearing armor or using a shield interferes with the somatic components of arcane spells, creating a risk of spell failure.  Bards and some other arcane classes can cast spells in light armor without this risk.

Material components
 * Casting a spell often requires that the caster sacrifice some sort of material component. Often, these components are virtually worthless, but some spells, such as spells to raise the dead, require material components costing thousands of gold pieces. If a caster is unable to access or use the correct spell component, the spell cannot be cast. As the spell is cast, the material component is destroyed, so it is not reusable in any way.

Magical focus
 * Alternatively, casting a spell may require that the caster have access to a holy symbol or other special object, to focus on when casting the spell. This is mostly true for divine spells. Foci are not damaged during the casting process and are reusable.