Those who pursue power through mysticism and spellcraft are magic-users. These men have devoted their lives thus far to the study of magic, so that they may work miracles through study like as clerics do by invoking the gods. While the rewards of powerful spells await them later in their careers, the starting magic-user has but one spell he may cast. He must memorize the spell from his spellbook, and cast the spell that same day or else loose it from his memory. Once a spell is cast, the magical energy actually leaves the caster's body, taking the memory of how to cast the spell with it. There is a chance, however, for magic-users of high or exceptional intelligence to be able to recall a cast spell – literally holding the magical energy in place with mental prowess. Otherwise, all cast spells must be re-memorized the following night.
A magic-user must have his hands free and be able to speak to cast a spell.
Intelligence is the prime requisite for magic-users, and they gain benefits for having high Intelligence scores (see Ability Scores).
Humans and demi-humans can all wield magic and progress as magic-users evenly at lower levels. Only at the highest levels do demi-humans slow in their advancement and full-blooded humans begin to outperform them.
All this studying has left the magic-user with little time for martial training, nor is it allowed. Each magic-user makes a pact with the shadow of night, that they will live by the spell, and defend themselves in combat with nothing but a dagger. Magic-users can wear no armor at 1st level, and only slowly over time learn to cast spells in armor.
At any time, the magic-user may research new spells. The magic-user may research a spell of any spell level that the magic-user is able to cast. Thus, a journeyman could research only 1st level spells, while a medium could research 3rd level spells. Your DM has guidelines for spell research.
Title: Journeyman XP: 0-2,250
HD: 1d4 Fights As: 1st level
Special Abilities: Each journeyman has a spellbook he was given at the end of his apprenticeship.
Spells in Spellbook: 4 1st level
Spells Memorized: 1 1st level
Journeymen can read and write in one of the languages they can speak (modified by Intelligence).
Limitations: Cannot wear armor while casting spells.
Obligations: Journeymen must give at least 100 gp per year to the regional guild of magic or incur their wrath.
Title: Prestidigitator XP: 2,251-4,500
HD: +1d4 Fights As: 1st level
Spells Memorized: 2 1st level
Prestidigitators can read and write in one more language they can speak.
Limitations: Prestidigitators may attempt to cast spells while wearing light padded armor, but with a 3 in 6 chance of spell failure.
Obligations: A prestidigitator must best one other magic-user each year in a magic duel (or at least one before leveling). The regional guild of magic expects 200 gp per year. They are expected to purchase any new spells.
Title: Medium XP: 4,501-9,000
HD: +1d4 Fights As: 1st level
2 1st level 1 2nd level
Mediums can read and write in one more language they can speak.
Limitations: Mediums may cast spells in light padded armor at no penalty or may attempt to cast spells in heavy padded armor or light leather armor with a 3 in 6 chance of spell failure.
Obligations: As per Journeyman, though guild dues are 40 gp per year, and duties may include supervising journeymen.
Witches (and warlocks) will likely never set foot in a wizard's guild, and have had no regimented schooling under a mentor. Instead, witches have been instructed in the casting of spells by otherworldly spirits. They are subject to the limitations of magic-users, but none of the obligations. The disadvantage of being a witch is that they do not have spellbooks. They only have access to the number of spells they can memorize, and use simpler memonic devices (beaded strings, clay tablets, etc.) to help them rememorize.