Arcane magic is the Art of drawing power from the world. A wizard learns magic by devoting long hours of study and practice to his Art. Many wizards take this so far that they seem to care only for their Art, even over family and friends.

A sorcerer, on the other hand, uses arcane magic naturally, usually unintentionally at first.

Limits: Only the most powerful wizards can heal and nothing short of the most powerful, highest guarded arcane spells can raise the dead, and those typically are at great risk to the caster.

Source: Arcane magic actually comes from the world itself, and is shaped by the will of the caster. As such, it is very draining on the caster. A wizard might easily drain himself of will power by over-exerting himself casting spells.

Methods: Wizards cast spells by reciting spells in obscure languages (typically draconic) and utilizing specific gestures and/or using items that may be consumed in the casting.

Casting Time: Varies. Usually measured in minutes. Arcane spells can be stored in items, such as wands or staves.

Organization: Most wizards are part of The Conclave, a government of, for, and by wizards. The government is based out of the Tower Magus near the borders of (name of countries?). The Council of Magi is a group of (?) wizards elected to make decisions for the wizards and a Archmage who acts as a president of the ruling body.

Most wizards view sorcerers with jealousy. To their mind, the wizard has devoted his life to discipline and control in order to grasp the power of magic, while a sorcerer has to sacrifice nothing. The sorcerer knows better, but their treatment generally fosters a mutual hatred.

Politics: Because they have given so much of their life to study, wizards are often sought out by rulers for their knowledge, wisdom, and power. These wizards often make use of these positions to manipulate events worldwide to their benefit or that of the Conclave.

Spells cast by priests are almost always divine in nature and are blessings from the Hundred Deities.

Limits: A priest must stay in good standing with his or her deity, or their prayers and spells will go unanswered. Divine magic is actually cast by the gods... the priest is just a conduit for that power.

Source: The Hundred Deities

Methods: Prayer and Worship

Casting Time: Varies. Usually measured in minutes. Some spells can be stored in items, such as wands or staves.

Organization: Varies by deity

Politics: Not all the of Hundred get along, and as can be expected, their quarrels often carry into their worshipers.

The Younger Gods draw their power from strange sources of elemental power. By combining elemental "strings" into more complicated "weaves" they manifest different abilities.

Limits: More complicated weaves require more strength and concentration, but it is safe to assume that most of the Younger are competent enough to perform almost any task

Casting Time: Varies. Usually measured in minutes. Arcane spells can be stored in items, such as wands or staves.

Linking: Channelers can link themselves to amplify their powers. There are limits to numbers, based on how they draw the power.

Witchcraft is a practice of drawing magic from the life force of creatures such as animals , demons, or humans.

Source: Living or once-living creatures

Methods: Most witchcraft is done in the form of rituals

Casting Time: Varies. Usually measured in hours or days.

Organization: Varies on society. In 'civilized lands' witches are generally feared or hated, though in need people will request their aid. In tribal societies, a shaman is often among the leaders of a tribe.