The captured spell book is a nebulous construct in BX and OSE. The item definitively exists in the game’s ruleset, yet comes with almost no explanation.
In OSE, this is all we get:
[Captured Spell Books: Without the use of magic (e.g. read magic), a spell book can only be read by its owner.]
That’s it. We have to infer everything else. And it’s not as though the captured spell book is a rarity; low-level MU and Elf PCs keel over regularly, leaving a pile of gear and a spell book on the floor of the dungeon between players who are left to wonder, “Well, what can we do with it?”
And sure, every referee probably has their own custom rules, but this is a RAW blog, so let’s see if we can piece together an objectively righteous baseline ruling.
1. You can read it.
As implied by the description, each spell book is written in a way that is completely unique to its author and owner. Casting Read Magic permanently enables the caster to read the text of that spell book.
The text of the spell book definition and rules then tells us:
“A character’s spell book contains exactly the number of spells that the character is capable of memorizing (as determined by the character’s class and level).”
If a character’s book can only contain the number of spells that the character can memorize, then a spell book is effectively a recorded reflection of the author’s mind. No more, and no less. And some readers take this to mean “You can only use your own spell book”, which then leads to making homebrew rulings like, “Captured spell books are used to offset the cost of magical research.”
Which is lovely, but it’s not RAW.
We don’t need homebrew to resolve this, though. Just note the specific language.
2. You can’t own it.
We’ve established that authorship dictates ownership. Your spell book contains exactly the number of spells that your character (its author and owner) can memorize. The captured spell book contains exactly the number of spells that its author could memorize. You can carry someone else’s book. You can translate and read someone else’s book. You just can’t own their book. It’s always theirs. Which brings us to the next point:
3. You can’t write in it.
Writing in a book contributes to authoring that book. We’ve established that authorship is ownership, and that book is already owned. If you were to record additional spells in that book, you would own it too, and that would violate the first rule of spell book ownership: your book contains the number of spells your character is capable of memorizing, so owning a second book of spells would exceed that number.
4. You can memorize from it.
If you can read it, you can memorize it. If you can memorize it, you can cast it. And this is where the RAW text, “the number of”, backs this argument. Because the rules do not say that a spell book contains exactly those spells you are capable of casting…. it says it contains exactly the number of spells you are capable of casting.
If you’re a 3rd level Elf, you can memorize exactly 3 spells. (1/1/2).
The spell book of your now-dead 3rd level MU companion also contains 3 spells (1/1/2).
Memorizing a spell from your companion’s book does not violate the recording limits of either book, nor does it violate the number of spells you can memorize, because that’s the number of spells you are capable of memorizing, not the number of spells available in the whole world that you could potentially or theoretically memorize. That number would technically be infinite, when you include magical research. So:
You could memorize any of 3 billion different spells.
You are capable of memorizing 3.
Your book can contain 3, the number you are capable of memorizing.
The captured book can contain 3, the number its owner was capable of memorizing.
You are capable of memorizing any 3 of those 6 spells.
And there we have it. No homebrew rulings, just the ink on the page.
5. You can’t copy from it for free
The game tells us there are only two ways to add spells to your book: Magical research at 1000gp/2w per spell level, or mentorship. If we take that at face value, there’s no shortcut to writing new spells into your book. It costs time and money to copy it yourself, or you get help from your mentor.
I know copying a spell from a captured book might seem wastefully redundant, but to reduce the encumbrance of adventuring with a set of encyclopedias strapped to one’s back, the caster might find it pragmatically expeditious to record the “best of” in their own book.
6. Value and narrative
In-world, magical versatility would be a reasonable thing to conflate with power and esteem among wizards. More spells, more power. But carrying a library around would be problematic, and hiring a retainer to carry the extra weight (a bodyguard bearer) would drain the party’s XP. So what’s a wizard to do?
Well, it stands to reason that this is why wizards build stronghold towers; to secure their libraries, and to dwell where they have instant access to the full catalog of their magic. They adventure to accumulate spell books and magic items and bring them back to their masters, establish a tower, and then take on apprentices (L1 Mediums) to send them out and reclaim captured spell books on their behalf.
And I think that’s a key Vancian dynamic that’s written between the lines of the BX and classic OSE game: The tenuous relationship between master and mentee casters. And I believe this is (sadly) often hand-waved, because it’s such a beautifully rich aspect of the world’s implied culture:
Each level 1 MU is sent adventuring with the same mission: Bring back more magic to the master—books, items for research, etc— and in exchange, the master will mentor you and teach you more spells. The more spells you bring back, the more spells the master can help you to learn. It’s mutually beneficial… until it isn’t…
Because at some point, it inevitably becomes treacherous. The master with a powerful pupil feels threatened (The question isn’t, “Are they holding out on me” but “How much!?”) and the pupil who approaches their master’s power might start to covet the very library they helped to build. It would be no surprise that Wizards shut themselves in their towers, trusting no one at the gates for fear of assassins, trapping their lairs against intruders and thieves, and generally becoming secretive hoarders as rumors spread among the townsfolk… and so on.
As always, food for thought at your table.
Thanks for reading!
"You see this." 
Leave a comment