Some arcane spellcasters rely on arcane writing and studying their personal notes on magic in the form of a spellbook. When such an arcane spellcaster prepares her spells for the day from her spellbook, she performs the rituals and incantations to cast the spell, pausing it just before the final step so that it is ready to released at a moment’s notice when needed.
An arcane spellcaster’s level limits the number of spells she can prepare and cast, but a high ability modifier might allow her to prepare a few extra spells each day. She can prepare the same spell more than once, but each preparation counts as one spell toward her daily limit. To prepare a spell the spellcaster’s ability score for casting must be at least 10 + the spellls level.
Requirements
Rest
To prepare her daily spells, a prepared arcane spellcaster must first benefit from a Long Rest, typically by sleeping for 8 hours. The spellcaster does not have to slumber for every minute of the time, but any activity which disrupts her long rest also disrupts her ability to prepare spells.
If her rest is interrupted, each interruption adds 1 hour to the total amount of time she has to rest in order to clear her mind, and she must have at least 1 hour of uninterrupted rest immediately prior to preparing her spells. If the character does not need to sleep for some reason, she still must have restful calm during her long rest before preparing any spells.
Recent Casting Limit/Rest Interruptions
If a spellcaster has cast spells recently, the drain on her resources reduces her capacity to prepare new spells. When she prepares spells for the coming day, all the spells she has cast within the last 8 hours count against her daily limit.
Preparation Environment
To prepare any spell, a spellcaster must have enough peace, quiet, and comfort to allow for proper concentration. Her surroundings need not be luxurious, but they must be free from overt distractions. Exposure to inclement weather prevents the necessary concentration, as does any injury or failed saving throw the character might experience while studying. Spellcasters who rely on a spellbook also must have access to their spellbooks to study from and sufficient light to read them by.
Spell Preparation Time
After resting, a prepared arcane spellcaster must study her spellbook to prepare any spells that day. 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.
Spell Selection and Preparation
Until she prepares spells from her spellbook, the only spells a spellcaster has available to cast are the ones that she already had prepared from the previous day and has not yet used. During the study period, she chooses which spells to prepare. If a spellcaster already has spells prepared (from the previous day) that she has not cast, she can abandon some or all of them to make room for new spells.
When preparing spells for the day, a prepared spellcaster can leave some of these spell slots open. Later during that day, she can repeat the preparation process as often as she likes, time and circumstances permitting. During these extra sessions of preparation, the spellcaster can fill these unused spell slots. She cannot, however, abandon a previously prepared spell to replace it with another one or fill a slot that is empty because she has cast a spell in the meantime. That sort of preparation requires a mind fresh from rest. Like the first session of the day, this preparation takes at least 15 minutes, and it takes longer if the wizard prepares more than one-quarter of her spells.
Spell 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. 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.
Prepared Spell Retention
Once a spellcaster prepares a spell, it remains in her mind as a nearly cast spell until she uses the prescribed components to complete and trigger it or until she abandons it. Certain other events, such as the effects of magic items or special attacks from monsters, can wipe a prepared spell from a character’s mind.
Death and Prepared Spell Retention
If a spellcaster dies, all prepared spells stored in his or her mind are wiped away. Potent magic (such as raise dead, resurrection, or true resurrection) can recover the lost energy when it recovers the character.
Wizard Spells and Borrowed Spellbooks
A wizard—or other arcane spellcaster who uses a spellbook—can use a borrowed spellbook to prepare a spell on her class spell list as long as it’s a spell level she can cast, but preparation success is not assured. First, the wizard must decipher the writing in the book (see Arcane Magical Writings). Once a spell from another spellcaster’s book is deciphered, the reader must make a Spellcraft check (DC 15 + spell’s level) to prepare the spell. If the check succeeds, the wizard can prepare the spell. She must repeat the check to prepare the spell again, no matter how many times she has prepared it before. If the check fails, she cannot try to prepare the spell from the same source again until the next day. However, as explained above, she does not need to repeat a check to decipher the writing.