I think this info is stated elsewhere, so sorry for the redundancy :x
Also, one more note: at the beginning, arcane spell casters may seem weak, as they will be limited by a small number of spell slots and level 1 spells which scale as the caster's level increases. However, they soon become very valuable and useful members of the party, and eventually become the most powerful characters bar none at the highest levels.
Err, just to state it more explicitly:
Their spell-casting abilities are Wisdom based, meaning the number of spell they can cast (i.e. number of spell slots--see below) is affected by Wisdom, the chance for a spell to be resisted or for saving throws to succeed is affected by Wisdom, etc. Note that for the most part any die rolls for things like the amount of damage done or the amount of healing done is typically not tied to Wisdom (unless stated otherwise), but is very often affected by the caster's level.
They must prepare each instance of a spell they cast every day (i.e. between rests). Each spell level is allotted a specific number of slots. That means if they want to cast a level 1 Heal Minor Wounds (whatever it's called) spell, they need to put two instances of Heal Minor Wounds each into a level 1 slot, using up two level 1 spell slots.
The base classes that operate like this are the druid and the cleric.
Arcane Spellcasters (Intelligence):
Their spell-casting abilities are Intelligence-based, and Intelligence affects their arcane spells in a way analogous to how Wisdom affects divine spells. Note again that die rolls for damage dealt, etc. are typically based on the caster's level and not their intelligence.
Again, these spell casters are allotted a number of spell slots per level, and they must assign specific instances of these spells. For example, if such a spell caster wants to cast the much-lauded (or much-feared) level 3 Fireball spell 3 times that day, they must use up three level 3 spell slots to be each occupied by an instance of the Fireball spell.
The wizard is the only arcane Intelligence-based caster. However, note that in exchange for a lack of flexibility and lower number of spells they can cast per day (compared to the sorcerer), they have the ability to learn new spells from scrolls using the "Inscribe Scroll" ability. What that means is that if a wizard finds a scroll for a spell that she likes and is has a high enough character level to cast it, she can put that spell into her spell book, and thus assign it to her spell slots for that spell level as she would any other spell from her spell book.
Arcane Spellcasters (Charism):
Their spell-casting abilities are Charisma-based, and Charisma affects their arcane spells in a way analogous to how Charisma affects divine spells, etc. Note again that die rolls for damage dealt, etc. are typically based on the caster's level and not their Charisma.
These spell casters operate differently than either the wizard or the divine spell casters: they are allotted a number of spells per spell level they can cast each day. However, the number of instances of particular spells does NOT have to be set beforehand. So you can cast any spell at any time as long you haven't ran out of spell slots for that level.
For instance, let's say you can cast the following level 1 spells: Color Spray, Magic Missile, and Shocking Grasp. And let's say you have 5 level 1 spell slots per day. Whenever you want, you can cast ANY of these spells. Any time you do so, you will lose a level 1 spell slot. So you could cast 5 Magic Missiles, 1 Color Spray and 4 Shocking Grasps, etc., without having to decide before hand how many instances of a particular spell you want to cast that day.
The arcane-based Charisma base classes are the bard and the sorcerer. The sorcerer is much like a wizard, except that each time she gains access to a new level of spells, she chooses which spells she will be able to cast, and that's it. She will never be able to choose other spells for that level. The up-shot is greater flexibility than the wizard and more spell castings per day. In addition to arcane spells, bard has a great many number of abilities, many of which are rogue-like, as well as bardic songs which are completely unique to the class and have a number of interesting and useful effects. On the other hand, they gain spell levels more slowly and have a smaller number of spell slots than the sorcerer.
Post edited November 30, 2010 by scyld