Can you write spells prepared with "knowledge pool" in your spellbook?

Question

Knowledge pool

At 7th level, when a magus prepares his magus spells, he can decide to expend 1 or more points from his arcane pool, up to his Intelligence bonus. For each point he expends, he can treat any one spell from the magus spell list as if it were in his spellbook and can prepare that spell as normal that day.[...]

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Replacing and Copying Spellbooks

A wizard can use the procedure for learning a spell to reconstruct a lost spellbook. If he already has a particular spell prepared, he can write it directly into a new book at the same cost required to write a spell into a spellbook.[...]

(The term wizard seems to mean arcane caster needing a spellbook in this context.)

If my magus uses the class feature knowledge pool to prepare a spell not in his spellbook, can he write that spell in his spellbook using the replacing procedure above? The rulebook talks about reconstructing a lost spellbook, but I don't think still having the spellbook is different from a stolen spellbook or an undamaged one forgotten at the bus stop, magic-wise.

Answer 1

A magus who prepares a spell using the class feature knowledge pool can copy that prepared spell into a spellbook—probably

That is, general consensus seems to be a tentative Yes in this 2011 Paizo messageboard thread. Developer Jason Bulmahn solicited opinions during the magus playtest as to whether this should be considered a bug or feature in this 2010 Paizo messageboard thread.

There is some discussion whether the magus technically understands the spell—a necessity when copying a spell from another caster's spellbook or from a scroll—but there's no allowance made for not understanding a spell that's already prepared, the assumption likely being if it's in your head, you understand it.

No one points to anything horribly unbalanced about this quirk, but several do voice that allowing the magus to do this makes them vaguely uncomfortable, but only insofar as such a process goes unmentioned in the magus's description.

Answer 2

RAW: Yes. The rules you cite would seem to allow it.

At my table: No.

• The point of having a limited-spells caster is to have their number of spells limited, otherwise it should just be a spontaneous "any spell on the list" caster like the cleric in the first place. It defies its own class design if interpreted in this way.
• It also makes a hybrid fighter/mage type better than any wizard at learning/researching spells, which is difficult to justify in the fiction and is generally genre-breaking.
• It then also allows all the other party member wizard types to get a lot of spells by asking the magus real nice, which seems unbalanced to me (I mean, you can take the point of view that "it's not really balance they should have anything they want" but that's not how the classes are designed).
• It removes access to new spells as a GM/quest carrot to use.

To me that's a lot of cons when the RAW seems like an unintended dodge anyway.