Can a wizard with multiple spellbooks use any spell in any spellbook with a bonded item?

Question

Suppose a wizard whose Arcane Bond is a bonded item. Suppose the wizard owns multiple spellbooks.

A bonded object can be used once per day to cast any one spell that the wizard has in his spellbook and is capable of casting, even if the spell is not prepared.

(Bolded for emphasis. Note the singular: compare "in one of his spellbooks".)

Can the wizard select any spell from any spellbook he owns? Or does each wizard have one "primary" spellbook, one that is the only usable option for the ability? If so, what determines what spellbook is the one?

What about proximity to said spellbook? Does the wizard need to carry a spellbook in order to use the 1/day bonded item ability?

Moreover, what does his spellbook actually mean? What determines whether the wizard owns the spellbook? For instance, if a wizard buys a half-filled spellbook from a second-hand wizardry store, and fills some pages of it, does that count as his spellbook even though he isn't the sole author? If that's not the case, how can a wizard make a used spellbook his own?

Answer 1

Short Answer

'his spellbook' should be changed to something more sensible, like "any of their spellbooks" or "any spellbook on their person". The rules expect, for absolutely no good reason, that each wizard has exactly one spellbook and they carry it on their person at all times except for rare occasions when they are securing it hidden away in some variety of magically protected vault. Magically protected vault think and on person think don't seem to be aware of each other and on person think definitely dominates.

It's an easy fix, though-- you can even fix it just by getting creative with your definition of 'his spellbook' and claim that the RAW kinda works¹

RAW Silliness

'his spellbook' is used several other times in the text. Let's look at what it means:

A wizard may know any number of spells. He must choose and prepare his spells ahead of time by getting 8 hours of sleep and spending 1 hour studying his spellbook. While studying, the wizard decides which spells to prepare.

A wizard begins play with a spellbook containing...

(emphasis added)

At each new wizard level, he gains two new spells of any spell level or levels that he can cast (based on his new wizard level) for his spellbook. At any time, a wizard can also add spells found in other wizards’ spellbooks to his own (see Magic).

Spells Gained at a New Level: Wizards perform a certain amount of spell research between adventures. Each time a character attains a new wizard level, he gains two spells of his choice to add to his spellbook. The two free spells must be of spell levels he can cast.

A wizard must study his spellbook each day to prepare his spells. He cannot prepare any spell not recorded in his spellbook, except for read magic, which all wizards can prepare from memory.

Wizards perform a certain amount of spell research between adventures. Each time a character attains a new wizard level, he gains two spells of his choice to add to his spellbook.

Wizards can add new spells to their spellbooks through several methods.

A wizard can also add a spell to his book whenever he encounters one on a magic scroll or in another wizard’s spellbook.

If the bearer is a caster who prepares arcane spells, he may prepare this spell as if it were in his spellbook.

(Wayfinders)

However, this would allow a wizard to copy a spell into his spellbook so he could prepare the spell from his book (assuming the spell takes up only one page...

(Memorize Page)

So, whatever 'his spellbook' is, it's the same 'his spellbook' that the Wizard has to study to prepare spells and that spells are instantly poofed into when the wizard levels up.

The spellbook a wizard starts with may or may not be 'his spellbook'; the rules refer to it only as a spellbook, much like those that can be purchased from the equipment section of the rulebook. Nonetheless, an entity need not be physically present to be studied, and adding spells to 'his spellbook' is possible both through levelling up and through the spell Memorize Page.

Since a wizard's spell are all in 'his spellbook' and a wizard preps by studying 'his spellbook' and adds spells to 'his spellbook' all without ever needing to physically interact with 'his spellbook' all you're doing by exploring the RAW wonkiness here is buffing wizards by making 'his spellbook' harder to destroy/endager/take away. That's... not really helpful for anything ever. Unless you're a wizard trying to protect 'his spellbook', which is currently a bunch of flamable paper in a backpack, in which case convincing your DM that 'his spellbook' is actually merely the platonic idea of a spellbook with no special relation to that specific physical copy may in fact be useful.

In any case, the RAW never specify what 'his spellbook' means, specifically, nor do they specify what ownership, possession, or 'his' means. Spellbook is relatively clear. Since the rules do not define these terms they are free to be defined however the GM sees fit, provided those definitions are compatible with the RAW.

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1 Specifically, define a spellbook broadly-- a wizard's spellbook is the thing they stores their spells in. If they store their spells in several books it is the collection rather than any individual book that is 'his spellbook'; the books merely serve as component parts. You can additionally specify that ownership is possession, and more specifically physical possession, so that books in the wizard's personal library back at their estate don't count as 'his'. While this works (the second order consequences for magic items that rely on ownership and such are very much in line with the theme imposed on the wizard by this limitation), it's definitely gymnastic and it's probably simpler just to replace the rule with an equivalent and more clear-on-its-face houserule.

Oh, and obviously the 'his' in his spellbook is gender neutral.

Answer 2

• Can the wizard select any spell from any spellbook he owns?
  What about proximity to said spellbook?

The intent seems to be, "any spell in his spellbook" means any spell that the wizard has learned.

Compare to this paragraph on wizards' spells known & learning new spells:

A wizard begins play with a spellbook containing all 0-level wizard spells (except those from his opposed schools, if any; see Arcane Schools) plus three 1st-level spells of his choice. The wizard also selects a number of additional 1st-level spells equal to his Intelligence modifier to add to the spellbook. At each new wizard level, he gains two new spells of any spell level or levels that he can cast (based on his new wizard level) for his spellbook. At any time, a wizard can also add spells found in other wizards’ spellbooks to his own (see Magic).

With this interpretation, "his spellbook" could be any number of physical books, and their actual location is irrelevant to the bonded item's ability.

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Not sure if this should be a separate question, but...

• What does his spellbook actually mean?

His spellbook is one that he wrote.

The SRD specifies what happens when you try to use a spellbook that you didn't write.

Another person’s magical writing remains incomprehensible to even the most powerful wizard until he takes time to study and decipher it.

After deciphering (Read Magic spell or Spellcraft check),

A wizard can use a borrowed spellbook to prepare a spell he already knows and has recorded in his own spellbook, but preparation success is not assured.
[...]
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.
[...]
He must repeat the check to prepare the spell again, no matter how many times he has prepared it before.

Answer 3

It would be the most recent spellbook he prepared his spells from.

As a Wizard with access to "any" spellbook can cast any spell contained within that he is capable of casting after some study.

This seems the most logical and elegant solution.