AD&D Primer: Magic
Magic is a powerful tool - and a powerful weapon - in Advanced Dungeons & Dragons. There is no real world corollary for magic, but fantasy stories are full of the stuff, from the ancient Greek play, Medea to Merlin and Morgan Le Fey in the Arthurian tales right up to the modern era in stories such as Tolkien's Lord of the Rings epic series.
In AD&D magic can be broken down into two general groups: spells cast by characters, NPCs and monsters, and magical effects for items such as damage bonuses for a sword. While the player will likely encounter lots of both in a game, it is the spellcasting that they have the most control over and also which needs further explanation.
While five of the seven classes have at least some spellcasting ability, it is what defines the magic user and to nearly the same extent the cleric and druid. Essentially though, there are two types of spells -Mage and Priest as explained below.
Mage spells, usable by magic user and rangers of 9th level and higher (only the the first two levels) consist of 9 "power" or difficulty levels. Many spells are oriented toward combat usage, both offensive and defensive, while others are for use outside of combat and may be protective in nature or utilitarian, working to aid the caster in some task. There is no simple categorization for the subject of the Mage spells, though there is a mechanical one.
Mage spells are learned either when the spellcaster gains a new level and has the opportunity to choose a spell to learn from a list of appropriate spells, or by scribing a spell, that is copying it, from a scroll or tome. Once learned, Mage spells must be memorized before being used. After a spell is cast, it must be rememorized before using again, however the spellcaster may have multiple spells of the same type memorized. The higher the level of the spell, the longer it takes for the spellcaster to memorize it, with a minimum of four hours to memorize even a single first level spell, though additional spells time of memorization is added in as low as 15 minute increments.
Of the two types of spells, Mage spells offer the greatest offensive potential, but are sonsiderably weaker in terms of healing the caster or other targets.
Priest spells, usable by clerics, paladins (9th level and higher), druids and rangers (8th level and higher), consist of 7 "power" or difficulty levels. While there are some offensive spells, the majority of Priest spells are either of a healing or a protective nature.
Unlike Mage spells, upon gaining a new level, spellcasters with the ability to cast Priest spells gain access to all spells of the appropriate levels. While unlike Mage spells in this manner, Priest spells must still be meditated upon before being cast, which is the exact same mechanic as memorizing a Mage spell. Likewise, after a Pries spell is cast, it must be meditated upon again before it can be used. The spellcaster may meditate upon multiple instances of the same spell.
Priest spells off the caster the opportunity to protect themselves and other before and during combat, as well as healing wounds, from the small scratches to raising the dead at higher levels.