Magic in the Known World

The Mortal Plane is the plane of the mundane and the non-magical, and therefore no magical spells come directly from this plane. Rather, what we call "magic" occurs when elements of the other planes, such as the Feywild or the Elemental Plane of Air, enter the Mortal Plane. For example, when casting a Fireball, the spellcaster opens a tiny gateway to the Elemental Plane of Fire, summoning that plane's supernatural essence into the Mortal Plane. Similarly, when a mage enchants a dagger to be magical, he is binding some magic from one or more of the other planes (depending on the type of enchantment) into the dagger. A Detect Magic spell is therefore able to detect the presence of material from other planes. An Identify spell can tell the caster exactly which planar materials are present. And a Dispel Magic spell will sever the connection between the object and the magic's origin plane, rendering the magic no longer active.  

Magic: Divine and Arcane

There are two basic types of magic. Divine magic spells are cast with the blessing of the gods, and rely on the channeling of divine powers by the spellcaster. Conversely, Arcane magic is the cast without the will or blessing of the gods. These spells both use magic, but the caster obtains the power in fundamentally different ways. In Roman society, legislation regarding magic applies to both, so "using magic in the commission of a crime" is equally wrong whether divine or arcane means are used.   When Divine Magic is used, the character's deity (or more often, one of the deity's emissaries, such as an angel or a deceased saint) summons the power of another dimension to the patron. The patron then bestows that power upon the spellcaster. Theoretically this is a "safe" way to cast magical spells, because the deity (or the god's designee) serves as an intermediary, protecting the caster from any unintended negative consequences of spellcasting. Although some divine casters such as Rangers or Druids may not openly worship a deity, nevertheless, because they are dedicated to nature, Diana watches over them and she or her emissaries provide the necessary magical powers. Thus, divine casters do not directly access the powers of the Planes.   When Arcane Magic is used, the character is directly accessing the powers of the inner or outer planes beyond the Mortal Lands. There is no intermediary here (even if the character worships a deity), but rather, the character is opening a channel to another realm, which can be quite dangerous, but also powerful. Consequently, arcane casters need something to mitigate against the danger, or suffer the consequences. Wizards mitigate the danger by intense study, learning how to cast spells without either overdrawing power or otherwise creating magical accidents. Warlocks rely on their patrons to provide protections, although the patron does not, as a cleric's deity, act as an intermediary; the patron simply provides the Warlock with the fortitude to withstand the planar energies and control them. Bards mitigate the risks by taming the planar energies with songs and poetry, or by learning lore much as a Wizard does. Sorcerers are the most powerful and dangerous of all, for they have no such defenses as a patron or scholarly learning, instead using the force of their own minds to bend the planar powers to their will. The exception is the Divine Soul sorcerer, who is protected from danger and guided by his or her deity.