Can a multiclassing Wizard/Magus cast a Wizard spell as a Magus spell?

Question

A close friend and I were wondering, if a Magus/Wizard share a spell from both of their spell lists, how it is cast in regards to usage and preparation. Say, a Magus has a spell in their Wizard spellbook. Can it be prepared and cast as a Magus spell?

Here's a relevant quote:

"A magus can learn spells from a wizard’s spellbook, just as a wizard can from a magus’s spellbook. The spells learned must be on the magus spell list, as normal. An alchemist can learn formulae from a magus’s spellbook, if the spells are also on the alchemist spell list. A magus cannot learn spells from an alchemist." -Pathfinder Advanced Player's Guide

Answer 1

Ambiguous. You'd at least be able to copy it over pretty easily (though that'd cost a bit of gold), thus having it in both formats. You could also prepare it via the borrowed-spellbook rules, and deciphering the writing would be automatic since you're the author, so you'd be able to do it with a spellcraft check (DC 15 + spell level, one check per preparation, on failure cannot prepare that spell again until tomorrow). However, to just prepare it directly, skipping that spellcraft check, is not clear from the RAW.

Answer 2

This has been discussed on the Paizo fora.

What I read from it is that, while the spellbook could be unique, the spells are still recorded separately. So if you know a certain spell as a Wizard spell but not its Magus variant, you shouldn't be able to prepare it as such.

There doesn't seem to be consensus on the question, though, and no official answer has appeared.

Answer 3

No

A multiclassed spellcaster uses their own preparation method and usage of spells in parallel. While a Wizard/Magus could learn Magus spells from Wizard spells and vice versa if they appear in both spell-lists, that still means they know the spell as a Magus spell and as a Wizard spell.

When casting a spell, the character must chose which casting mechanic they wish to use, and pick that kind of spell. So it is not possible to cast a Wizard spell as a Magus spell.

The most notable case where this matters is if when the spells appear at different spell levels in their respective spell-lists of the multiclass character:

• Firstly, this limits cross class learning (you can only learn and prepare spells available to your level in the class).

• Secondly, this shuts down attempts like "Well I know this spell as this class, but as my second class it is a higher spell level spell, so I can cast it as that class to gain benefits", which is clearly wrong.