I'm multiclassing as a Wizard2/Cleric3. I'm wondering if it's possible to prepare a spell from the cleric spell list and then if it's also found in the Wizard spell list, would I be able to write it down in my wizard spellbook?
I'm confused by this as the PHB states that if I find a scroll or a book, I can decipher it and boom, it's in my own book. I'm essentially my own walking book book. I've found this in the sidebar in the PHB under wizard regarding spellbooks.
Replacing the Book. You can copy a spell form your own spellbook into another book-for example, if you want too make a backup copy of your spellbook. This is just like copying a new spell into your spellbook, but faster and easier since you understand your own notation and already know how to cast the spell. You spend only 1 hour and 10gp for each level of the copied spell.
If you lose your spellbook, you can use the same procedure to transcribe the spells that you have prepared into a new spellbook. Filling out the remainder of yourspellbook requires you to find new spells to do so, as normal. For this reason, many wizards keep backup spellbooks in a safe place.
Now, lets say that I prepare Protection from Evil and Good, which is a 1st level spell and can both be found in the Cleric spells list and in the Wizard spell list. Shouldn't it be possible for me to write it down into my spellbook by following the given formula in the "Replacing the Book"; 10gp + 1hour for each level of the copied spell.
I understand that it would have been very different if the holder of the spell I want to copy is another creature (party member or not) but now it's all me. I know the spells, I own the book, I am the Wizard.
Best Answer
No you cannot transfer spells prepared as a Cleric into your spellbook
Just above the text that you reference, the sidebar in the PHB explains
The fact that the book explicitly says that it contains wizard spells is the killer here. Spells that you prepare as a cleric are not wizard spells. They are cleric spells, even if they are on the same spell list.
We know this because of the rules for multiclass spellcasters (PHB pg. 164)
From this, we establish that your prepared spells as a cleric are "Cleric Spells" in that they are prepared as a cleric, and cast as a cleric; not as a wizard. And your prepared spells from your spellbook are "wizard spells" for a similar reason. Even if the two appear on the same spell list, each spell you have prepared is associated only with one of your classes.
The PHB then goes onto explain that when copying spells from spellbook to spellbook:
If copying from book to book is the same as adding new spells except faster, then we know that you can only transfer over wizard spells since you can only copy new wizard spells into the spellbook.
Finally, As you have pointed out:
The procedure in question is the same as copying over a new spell, or a spell from one book to another. Both of these processes require wizard spells to work. Thus, even though copying a spell down from memory doesn't specifically add any new restriction, it doesn't explicitly lift the general limitation on the procedure; the precondition that the spell in question is a wizard spell.