Preparing Arcane Spells
A wizard's level limits the number of spells she can prepare and cast. A wizard's high Intelligence score might allow her to prepare a few extra spells. She can prepare the same spell more than once, but each preparation counts as one spell toward her daily limit. Preparing arcane spells is an arduous mental task. To do so, the wizard must have an Intelligence score of at least 10 plus the spell's level. Rest: To prepare her daily spells, a wizard must have a clear mind. To clear her mind, the wizard must first sleep for 8 hours. The character does not have to slumber for every minute of the time, but she must refrain from movement, combat, spellcasting, skill use, conversation, or any other fairly demanding physical or mental task during the rest period. If the wizard's 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 the wizard must have at least 1 hour of rest immediately prior to preparing her spells. If the character does not need to sleep for some reason, she still must have 8 hours of restful calm before preparing any spells.
Recent Casting Limit/Rest Interruptions: If a wizard 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 spells she has cast within the last 8 hours count against her daily limit.
Preparation Environment: To prepare any spell, the wizard must have enough peace, quiet, and comfort to allow for proper concentration. The wizard's surroundings need not be luxurious, but they must be free from overt distractions, such as combat raging nearby or other loud noises. Exposure to inclement weather prevents the necessary concentration, as does any injury or failed saving throw the character might suffer while studying. Wizards also must have access to their spellbooks to study from and sufficient light to read them by.
One major exception: A wizard can prepare a read magic spell even without a spellbook. A great portion of a wizard's initial training goes into mastering this minor but vital feat of magic.
Spell Preparation Time: After resting, a wizard must study her spellbook to prepare any spells that day. If the character 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 wizard 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, a wizard chooses which spells to prepare. The act of preparing a spell is actually the first step in casting it. A spell is designed in such a way that it has an interruption point near its end. This allows a wizard to cast most of the spell ahead of time and finish the spell when it's needed, even if the character is under considerable pressure. The wizard's spellbook serves as a guide to the mental exercises the wizard must perform to create the spell's effect. If a wizard 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, the wizard can leave some spell slots open. Later during that day, the wizard can repeat the preparation process as often as she likes, time and circumstances permitting. During these extra sessions of preparation, a wizard 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.
Prepared Spell Retention: Once a wizard 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). Upon casting, the spell's energy is expended and purged from the character, leaving her feeling a little tired. 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 the character dies, all spells stored in her mind are wiped away.
Arcane Magical Writings
To decipher an arcane magical writing (such as a single spell in written form in another's spellbook or on a scroll), a character must make a successful Spellcraft check (DC 20 + the spell's level). If the skill check fails, the character cannot attempt to read that particular spell until the next day. A read magic spell automatically deciphers a magical writing without a skill check. If the person who created the magical writing is on hand to help the reader, success is also automatic.
Once a character deciphers a particular magical writing, she does not need to decipher it again. Deciphering a magical writing allows the reader to identify the spell and gives some idea of its effects (as explained in the spell description). If the magical writing was a scroll and the reader can cast arcane spells, she can attempt to use the scroll.
Wizard Spells and Borrowed Spellbooks
A wizard can use a borrowed spellbook to prepare a spell she already knows and has recorded in her own spellbook, but preparation success is not assured. First, the wizard must decipher the writing in the book (see Arcane Magical Writings, above). Once a spell from another spellcaster's book is deciphered, the reader must make a successful 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 the spell 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.)
Adding Spells to a Wizard's Spellbook
Wizards can add new spells to their spellbooks through several methods. If a wizard has chosen to specialize in a school of magic, she can learn spells only from schools she can cast.
Spells Copied from Another's Spellbook or a Scroll: A wizard can also add spells to her book whenever she encounters a new spell on a magic scroll or in another wizard's spellbook. No matter what the spell's source, the character must first decipher the magical writing (see Arcane Magical Writings, above). Next, the wizard must spend a day studying the spell. At the end of the day, the character must make a Spellcraft check (DC 15 + spell's level). A wizard who has specialized in a school of spells gains a +2 bonus to the check if the new spell is from her specialty school. She cannot, however, learn any spells from her prohibited schools.
If the check succeeds, the wizard understands the spell and can copy it into her spellbook (see Writing a New Spell into a Spellbook, below). The process leaves a spellbook that was copied from unharmed, but a spell successfully copied from a magic scroll disappears from the scroll.
If the check fails, the wizard cannot understand the spell and cannot attempt to learn it again even if she studies it from another source until she gains another rank in Spellcraft. If the check fails, the character cannot copy the spell from another's spellbook, and the spell does not vanish from the scroll.
Independent Research: A wizard also can research a spell independently, duplicating an existing spell or creating an entirely new one.
Writing a New Spell into a Spellbook
Once a wizard understands a new spell, she can record it into her spellbook.
Time: The process requires 1 day plus 1 additional day per spell level. Zero-level spells require 1 day.
Space in the Spellbook: A spell takes up 2 pages of the spellbook per spell level (so a 2nd-level spell takes 4 pages, a 5th-level spell takes 10 pages, and so forth). A 0-level spell (cantrip) takes but a single page. A spellbook has 100 pages.
Materials and Costs: Materials for writing the spell (special quills, inks, and other supplies) cost 100 gp per page.
Note that a wizard does not have to pay these costs in time or gold for the spells she gains for free at each new level. The wizard adds these to her spellbook as part of her ongoing research.
Replacing and Copying Spellbooks
A wizard can use the procedure for learning a spell to reconstruct a lost spellbook. If she already has a particular spell prepared, she can write it directly into a new book at a cost of 100 gp per page (as noted in Writing a New Spell into a Spellbook). The process wipes the prepared spell from her mind, just as casting it would. If she does not have the spell prepared, she can prepare it from a borrowed spellbook and then write it into a new book.
Duplicating an existing spellbook uses the same procedure as replacing it, except that the task is much easier. The time requirement and cost per page are halved.