1) CL Minimums
You can cast a spell at a lower caster level than normal, but the caster level you choose must be high enough for you to cast the spell in question, and all level-dependent features must be based on the same caster level.2) Minimum spellcasting ability score:
To prepare a spell the wizard must have an Intelligence score of at least 10 + the spell’s level. ... A spellcaster always has the option to fill a higher-level spell slot with a lower-level spell. A spellcaster who lacks a high enough ability score to cast spells that would otherwise be his or her due still gets the slots but must fill them with spells of lower level.
I find it strange that the rules are presented for wizards. Perhaps the RC has a more generic version? I'm lazy.3) The ability to cast spells
(which almost always comes from a class). Example:
A bard casts arcane spells.... He can cast any spell he knows without preparing it ahead of time4)
You can only refresh spells 1/day:
After resting, a wizard must study her spellbook to prepare any spells that day. ... When preparing spells for the day,5)
During 1/day refreshes, no refreshing slots used too recently
When she prepares spells for the coming day, all the spells she has cast within the last 8 hours count against her daily limit. ... As with wizards, any spells cast within the last 8 hours count against the sorcerer’s or bard’s daily limit.6) Resting time
To prepare her daily spells, a wizard must first sleep for 8 hours. ... A sorcerer or bard needs 8 hours of rest (just like a wizard)7) Spell renewal time
of 1 hour or 15 minutes:
If she wants to prepare all her spells, the process takes 1 hour. Preparing some smaller portion of her daily capacity takes a proportionally smaller amount of time, but always at least 15 minutes, the minimum time required to achieve the proper mental state. ... he spends 15 minutes concentrating. (A bard must sing, recite, or play an instrument of some kind while concentrating.) During this period, the sorcerer or bard readies his mind to cast his daily allotment of spells. Without such a period to refresh himself, the character does not regain the spell slots he used up the day before.8) Casting aids
(only for some casters or spells):
There is one major exception: A wizard can prepare a read magic spell even without a spellbook. ... a wizard must study her spellbook to prepare any spells that day.9) Spells Known
First you must choose which spell to cast. ... If you’re a bard or sorcerer, you can select any spell you know.
Some classes (such as cleric) know all their spells. Wizards have special rules about their spellbook. Who wants to find those for me?10) Slots
The various character class tables show how many spells of each level a character can cast per day. These openings for daily spells are called spell slots.11) High enough level
In addition to having a high ability score, a spellcaster must be of high enough class level to be able to cast spells of a given spell level.
This extremely relevant rule is buried in the ability score area. I have no idea why. Also it nebulously references what we know to be your classes spell table progression (see above)12) Spell Requirements
To cast a spell, you must be able to speak (if the spell has a verbal component), gesture (if it has a somatic component), and manipulate the material components or focus (if any)
Additional components have additional text in the preceding the spell text in the book they are found. For instance Abstinence components are in BoED.13) Casting interruption:
If something interrupts your concentration while you’re casting, you must make a Concentration check or lose the spell.
There are various anooyances, most all of which force oncentration checks. Likewise, counterspelling is a kind of interruption to normal spellcasting that can make casting not work.14)
Once the spell takes effect
, various things can make it not do much. See stacking rules
. Other situations would be antimagic fields
, wild magic zones etc.
So what did I miss? I'm sure its a few. I'll re-order these once we think we've finished the list entirely.