Arcane Magic

Arcane magic is widely practiced and can be found almost anywhere. It is incredibly powerful, and often leads to as many failures as it does successes. Its practitioners are referred to as arcanists, but most prefer the terms 'mage', 'wizard', or 'sorcerer'.
The energy that feeds all arcane power is largely a mystery, but most speculation seems to suggest it originates from a plane of energy somewhere in the flux between the positive and negative material plane. Through mental -and to a lesser degree, physical- channeling, an archanist can tap into this energy, where it manifests as a spell's effect. Such as explosive flame, powerful force or an impenetrable shield.
Arcane magic is incredibly flexible and can be manipulated at extremely small levels to create intensely useful or powerful things. Two common things that can be made with arcane powers are Potions and Spell Scrolls.
The origin of arcane magic is blurred, but an expert would tell you that it is a development of 'Old Magic'; a form of magic that much more heavily relied on the mind to manifest power but when that turned out to damage the user, arcanism became infinitely more prevalent.

Schools of Magic

Modern arcanism has been around for far longer than the old magics, thus it has had a lot more time to develop into something greater; the different ways in which energy can be harnessed cna be sorted into eight categories: Abjuration, Alteration, Conjuration/Summoning, Divination, Enchatment/Charm, Illusion/Phantasm, Invocation/Evocation and Necromancy.

Abjuration

Abjuration is the study of protection and simple wardings. Spells of this school focus magical energies to provide protection. This protection can take a number of forms, including warding off specific types of weapons or creatures and discouraging or dispelling enemies. The school also includes a variety of spells involving avoidance and repellence. Abjuration spells concentrate on eliminating or hindering sources of potential harm rather than repairing damage.
There are three general types of abjuration spells: protective, dispelling, and dismissal. Protective spells include those that offer protection from creatures (such as protection from evil), those that protect against weapons (such as protection from normal missiles), and those that protect against certain types of magic (such as minor globe of invulnerability). Dispelling spells cause the elimination of specific magical effects, such as dispel magic and remove curse. Dismissal spells cause the removal of certain creatures, such as dismissal and banishment.
Since the most effective abjurations are those offering the greatest protection, it seems that the dismissal spells are the most desirable-- after all, they get rid of the attacker altogether. However, dismissal spells are effective only against very specific types of attackers, such as banishment 's dismissal of extraplanar creatures. Unless the wizard anticipates encountering the type of creature affected, a dismissal spell won't be helpful. Since protection spells usually affect only a single individual, the best all-purpose abjurations are the dispelling spells; dispel magic for instance, employed against a magic-wielding enemy protects not only the caster, but the entire party.

Alteration

Alteration is the study of change; altering things about the known world to grant it different effects. Spells of this school enable the caster to channel magical energies to cause direct and specific change in an existing object, creature, or condition. Alterations can affect a subject's form, weight, abilities, location, or even their physical well-being.
No school has a wider variety of spells than the school of alteration, making the transmuter the most versatile of all the specialists. The available spells can be assigned to six general groups:
* Defensive Spells. This group of protective spells offers defensive capabilities rivaling those of the abjuration school. This group includes spells that limit an opponent's ability to attack, such as fog cloud, solid fog, slow, and darkness and also spells that provide direct protection to the caster and his party, such as stoneskin and Leomund's tiny hut.
* Offensive Spells. This group includes spells such as strength and haste which increase the party's chance to inflict damage, and spells such as Melf's minute meteors and death fog which inflict damage directly.
* Mobility Spells. This group includes fly, blink, passwall, and teleport and other spells that improve the caster's ability to move from place to place.
* Security Spells. This group enables the caster to protect objects and places, and includes spells such as wizard lock, guards and wards, and Leomund's secret chest.
* Talent Spells. This group gives the caster (or a person of the caster's choice) a temporary talent, usually one that duplicates a special ability of another creature or race. Such spells include infravision, water breathing, and tongues.
* Special Spells. This group encompasses a wide range of spells that don't fit into into any of the previous categories, such as magic mouth, mending, message, and fool's gold. Because of the variety of spells available, a transmuter can assume a number of different roles in an adventuring party. For instance, a transmuter who knows a number of offensive spells can battle effectively alongside a party's warriors. A transmuter who knows a few mobility spells in addition to some offensive spells makes an especially impressive combatant (imagine a flying transmuter soaring to the top of a tree, then casting Melf's minute meteors at an unsuspecting enemy). With a supply of defensive spells, a transmuter can assume many of the functions of an abjurer. A transmuter with spider climb, deeppockets, and knock is a good substitution for a thief; add polymorph self and passwall, and you'd be hard-pressed to find a better spy. The transmuter always runs the risk of being overwhelmed by the sheer volume of available spells and making haphazard or ill-informed decisions about which spells he learns and memorizes. Therefore, he must take care to balance his spell choices with the needs of his party.

Conjuration and Summoning

This school includes two different types of magic, though both involve bringing in matter from another place. Conjuration spells produce various forms of non-living matter. Summoning spells entice or compel creatures to come to the caster, as well as allowing the caster to channel forces from other planes. Since the casting techniques and ability requirements are the same for both types of magic, conjuration and summoning are considered two parts of the same school.
Although the conjurer doesn't have an excessive number of specialty spells from which to choose, spells of the conjuration/summoning school are among the most potent of all, comparable only to the school of necromancy in sheer power.
Though useful in a wide variety of situations, conjuration/summoning spells are particularly effective in combat, since the majority of them are capable of inflicting damage.
Generally, conjuration spells such as Melf's acid arrow inflict damage directly, while summoning spells, such as monster summoning, use an intermediary force or monster to attack opponents. Direct attacks have the advantage of immediacy; Melf's acid arrow, for instance, is sent directly at its target. Indirect attacks using an intermediary have the advantage of versatility; giant rats summoned by monster summoning I can be directed to attack the stationary Opponent No. 1, then can be ordered to run down the fleeing Opponent No. 2.
Many summoning attacks require the continual participation of the conjurer; he can't control his summoned creatures if he can't communicate with them. This is especially crucial with spells such as conjure elemental, where the summoned creature will turn on the conjurer if the conjurer breaks his concentration.

Divination

Among the oldest forms of magic are the predictive ones; Divination is the study of discovery. This school includes a variety of spells that reveal information that would otherwise remain hidden or secret. Greater divination spells reveal the existence of specific items, creatures, or conditions, as well as information about the past, present, and future. This school also includes spells that contact creatures from other planes of existence, but do not induce direct action from those creatures.
The variety of spells available to the diviner is more restricted than any other school or specialist. Offensive spells -- that is, those that inflict damage on opponents either directly or indirectly -- are nonexistent for this school. Defensive spells that either inhibit an enemy's attack ability or provide direct protection for the diviner and his companions are likewise unavailable. This doesn't mean that the diviner is useless on the battlefield; it means that his strength lies elsewhere.
As a gatherer of information, the diviner is without peer. A diviner can anticipate unexpected dangers, can separate the truth from lies, and is exceptionally effective as a spy. He can bolster his party's defenses by alerting them to the presence of normally undetectable opponents. Although the repertoire of divination spells is relatively small, the diviner has access to more schools than any other specialist.
There are two general groups of greater divination spells. One group includes spells that reveal information about a specific object or creature, such as ESP and locate object. A second group reveals information about any type of object or creature within the range of the spell; this group includes detect invisibility and clairvoyance.

Enchantment and Charm

Enchantment is among the most common forms of magic; a lot of powerful people will seek out and pay large sums of money to those who can enchant equipment, but this school also includes another sype of magic. Both types imbue their subjects with magical energy to create specific effects. Charm spells induce changes or influence the behavior of creatures, usually altering their subject's mental or emotional states. Enchantment spells invest non-living objects with magical powers.
The enchanter has a moderate number of spells from which to choose, most of them emphasizing defensive rather than offensive effects. Not only can this school of spells be divided into charms and enchantments, the spells can also be divided into those that affect only a single person or object, and those capable of affecting a group.
The shortcoming of the enchantment/charm catalog is the lack of offensive spells. Only a handful of them are capable of inflicting damage. This usually defines the enchanter's role in an adventuring party as defensive. As with the abjurer, it should be noted that with his little armour, the enchanter is extremely vulnerable to attacks. Unlike an abjurer, whose defensive spells operate more or less automatically, the enchanter's defensive spells often require him to take an additional action after they are successfully cast. A hypnotized victim, for instance, needs to be told what to do, as does a subject affected by suggestion. Charmed creatures may simply stand and stare unless directed otherwise by the caster. Clearly, the most effective enchanters are those who are creative, quick-thinking, and vigilant.

Illusion and Phantasm

Illusion magic is formidable and is occasionally thought (among great discussion) the most powerful school of magic. Spells from the school of illusion bend reality to create apparent changes in the environment, in the caster, or in other persons or creatures. These spells do not cause real changes as alteration spells do, but instead alter the way that creatures and persons perceive reality. This school includes both illusion and phantasm spells.
Illusions are spells that simulate reality, creating artificial conditions of light, color, sound, and scent. Audible glamer is an example of an illusion that simulates sound. In general, the lower-level illusions are of limited use in combat situations, providing neither direct protection from damage nor the ability to inflict damage on opponents. Though most illusions create only the appearance of reality, some high-level spells tap extradimensional forces to create illusions with physical substance, capable of inflicting damage and otherwise interacting with the real world. Shadow monsters is an example of a quasi-real illusion. These are the most useful types of illusion spells in combat, as they can create illusionary creatures to attack opponents and execute an assortment of other tactical actions.

Invocation and Evocation

This school includes two types of spells, both of which use magical energy to create specific effects by bringing forth special forces that the caster shapes into constructs of energy or constructs of matter. Evocation spells use the natural magical forces of the planes. Invocation spells call on the intervention of powerful extradimensional beings.
This school offers the specialist a range of spells of staggering power. In fact, no school has a wider variety of offensive spells available at all levels. The invoker also has access to a number of potent defensive spells. Some of these provide protection against specific types of attacks, such as shield and fire shield, while others offer protection by hindering the actions of all enemies within the range of the spell, such as wall of fog and shout. Generally, the spells hindering enemy actions will prove to be more useful than spells protecting against a specific type of attack, unless the invoker suspects that he will be encountering specific types of monsters. For instance, if fire lizards roam the land, it's prudent to memorize fire shield.

Necromancy

Among the least popular schools due to taboo, this powerful school involves spells dealing with death and the dead. These spells drain vitality from living creatures and restore life functions to unliving creatures. Bones, blood, spirits, and apparitions are all associated with the magical energies shaped and controlled by the specialists of this school.
Necromantic spells can be sorted into three general groups. One group includes spells that imbue the caster or a person of the caster's choice with special abilities similar to the effects of certain enchantment and alteration spells. Chill touch, enervation, death spell, and finger of death are examples of this type of spell. The majority of this group are extremely powerful offensive spells; death spell and finger of death in particular are effective against a wide range of opponents. A necromancer armed with a repertoire of these spells bolsters his party's offensive capabilities considerably. Reincarnation can be considered part of this group, since it imbues the subject with a special ability; namely, a second chance at life.
A second group of necromancy spells includes those that create creatures or physical forces to fight on the caster's behalf. Spectral hand and animate dead are examples. Summon shadow is also included in this group, although in this case, an actual creature is summoned rather than created. Since these spells enhance the caster's ability to inflict damage on opponents, they can be considered offensive spells.
A third group of necromancy spells enables the caster to affect the actions of other creatures, usually undead. Hold undead, contagion, and control undead are examples. Since these spells inhibit the attack capabilities of the affected creatures, they can be considered defensive spells, although in the case of control undead, the affected creatures can also be used to attack enemies.