I got a rules question about finding spellbooks.

Normally if your Wizard finds another Wizard's spellbook, they can use it to copy spells into their own spellbook.

However is it possible to simply swap over to that new spellbook and use it as if it was your own and prepare spells from this spellbook? Could you then copy spells from your previous spellbook as per the rules for making a back-up spellbook (aka at the low copy cost)?

What happens when you find a magic item, like an Arcane Grimoire, which presumably have spells written in it from its previous owners? When you want to attune to the book and use it as your spellbook, what happens to the spells already written in the book?

I found myself in the situation that I had found a magic item spellbook whose owner our party had defeated. I wanted to use the spellbook for its benefits but I'm a little puzzled by how that mechanically works on a RAW / RAI basis?

I don’t think you can simply transition to using someone else’s book. The entire point of the need for time and gold to scribe found spells is that you need to work out the notation you found and practice casting the spell yourself. The magic item books that come with certain pre-loaded spells are a specific exception. In your scenario, since Arcane Grimoires aren’t pre-loaded this way, I’d say anything already in the book that you don’t already have still costs the full rate to learn and be able to prepare, and you can copy your already known from your current book to it at the reduced rate. Really, the thing to remember is that the RAW of learning spells as a Wizard is not dependent on the act of writing out the learned spell; if you find a spell you did not learn via level up, you can spend the appropriate time and gold to learn it. Where that spell is ultimately transcribed is more cosmetic than mechanical.

I’d agree with Aceofrogues. I think the default idea is that each wizard has their own system for noting how to cast a spell. So when you learn one from a spellbook or a scroll, part of the time involved is basically translating the other wizard’s style into your own. So you can’t just start using someone else’s book. 
And if you find spells in an arcane grimoire, you’d need to re-copy them for that same reason. 

That said, ask your DM. Maybe magic is standardized in your world and anyone can use anyone else’s spells. 

It’s ultimately not so much a setting thing as a game mechanics one; you learn 2 spells per level and if the DM provides the option can spend time and gold to learn more. That’s what RAW boils down to for Wizards, regardless of where the exact disposition of the additional spells before, during, or after you pay the cost. The DM is of course still free to rule differently, if they want.

So as I know it and as I have run it each wizard has there own short hand and how they handle/feel when channeling the energy for spells. So to each wizard its a little different you can see that a spell maybe a fireball spell in that book but you know you thumb would be in a different place for you and the way you say x word might have a different tone to you can cast the spell. Each person takes notes differently IRL and some are a lot harder to follow then others..... its kind a the same thing as a wizards spell book they could read the one that isn't there's but they need to understand it too and then make that spell there own and copy it into there own book.

Now that said if a player wanted to try and use a spell from someone else book I may have them do a arcane check base 10 + level of the spell so they could prepare the spell. But I might give the spell like a 5-10% chance to just fail. no spell lot used since they couldn't do it right they just lost the prepped spell slot for the day. But that would be my own homebrew in that situation.

Quote from Iteration152 >>

However is it possible to simply swap over to that new spellbook and use it as if it was your own and prepare spells from this spellbook? Could you then copy spells from your previous spellbook as per the rules for making a back-up spellbook (aka at the low copy cost)?

 

 
You can use any spellbook to prepare your spells from. However, the spells the previous wrote will not be usable to you. You will need to transcribe them - at full cost. This is because every wizard uses their own cypher and notation system. 

From the Wizard's spellcasting feature:

"Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation."

The discount for "replacing" your spellbook only apply to spells you have previously learned/transcribed because they are already in your own notation system. 

So, for example if the Arcane Grimoire was found with some spells in it, you would have to still transcribe the spells - even back into the grimoire - using your own system. Whether you do that or not your are free to copy (at discount) your own spells from your current spellbook into the grimoire and use the grimoire as your spellbook.

Certain magical spellbooks like the Atlas of Endless Horizons, for example, have an exception:

"When found, the book contains the following spells, which are wizard spells for you while you are attuned to the book: arcane gate, dimension door, gate, misty step, plane shift, teleportation circle, and word of recall. It functions as a spellbook for you."

This means while attuned to the book you may use those spells as if they were your own spells because the magic of the item lets you. This is only because the specific rule detailed in the item description says so (specific beats general). It would not apply to the Arcane Grimoire since it has no exception written in the description.

I hope this makes sense.

I'd say any sane wizard who finds another spellbook simply keeps both. Why would he ever go the the pointless trouble of copying the spells over? Either he can read them, or he cannot. Anything else is utter junk. The whole thing is there are some sort of pseudo-explanation for why spellbooks aren't mass produced - and it's no less junk for that, because it doesn't explain anything. You have a common trade language - but the most intelligent people in the world weren't ever clever enough to produce a common shorthand for spell casting? 

So. Back in his tower, any sane wizard keeps all the spellbooks he took off other - now diseased - casters. On his person, he carries a master book into which he's paid a scribe to copy all the spells. And finally, he has a copy of his master spellbook kept safe in some third, secret location. Like a bank.

And all the inept excuses and fabulations of the devs be damned.

In a strange and bizarre turn of events, I am oddly in agreement with Acromos. 

The scribing system is a poor attempt at game mechanic balance in a place where none is even needed (since the DM has full control over what spells the party wizard can come across or get access to). 

Quote from Cyb3rM1nd >>

In a strange and bizarre turn of events, I am oddly in agreement with Acromos. 

The scribing system is a poor attempt at game mechanic balance in a place where none is even needed (since the DM has full control over what spells the party wizard can come across or get access to). 

 Unheard of! =)

Yea, I'm basically always trying to swim against the current. It's my accepted role in life =)

The key point is that it takes more than just “say X words while holding your hand in Y position with Z item held in one”; you need to understand the underlying mechanics and forces at play. Ergo the lengthy notes, and given the setting a lack of standardization is to be expected (do you know how long it took for spelling to become standardized, let alone things like accounting?). It’s like learning a new piece of music, not just copying someone’s answers on a test.

Any books we found we just kept.

Think of it this way. If all the spells in the book were scrolls exactly how valuable would the book be?

The true cost of being a low level wizard is spending all your free cash on copying spells and making scrolls. As you gain levels you find less spells to copy and keep more free cash to fund a laboratory. or at least a home to do research in.

Half the reason for being a wizard is to find all the spell knowledge they can and gathering as many spell books as possible is a huge part of that.  The cost and time of putting the spell into your own book was the reason the Copy Spell was removed from 5e.

Any spells our characters could use at that level we copied into our own spell books and kept the original book for reference as we gained levels.

What do you think is in all those books wizards have in their labs? Other wizards spell books and their own notes on new spells. Add in their notes on making the inks they need and the locations of components in the area. They are the scientists of their day. They would have books on alchemy and herbs. The stars and other stellar objects. Teleportation circle coordinates.

Quote from MaximusCathril >>

 And what if the spell book is in a language that your character can’t read, instantly you know what the scribble says and means as soon as you find another casters spell book?

maybe a book contains magic spells the author didn’t want out into the unknown to be had by all because it is potentially so powerful that it would be abused in ways the author could never have imagined, and so they encrypted it?

what if the reason to have to translate is so the time between getting a spell you can’t yet cast, but can research and work on to discover how it works is right as you gain the ability ( class level up ) to cast and use it effectively?

 I ... I'm afraid I don't really get your point. If it's in a foreign language, you get it translated, or use a spell.

Magic spells are bog standard, why would any caster dream that his fireball spell was any different than all the others out there? I get what you're saying, but this game doesn't support what you're going for. There's an Ye Olden Magic Item Shoppe on every corner (by which I mean the gold-becomes-power mechanic is ingrained in the very fabric, the substructure of the game), where you can buy Nuclear Bomb Golems if you have money enough. Why would Jimmy the Mage's Chill Touch spell be something too dark for the world?

That third one. So you're saying .. what if you have to wait to level up before you can cast the spell you just found? Yes, so what? 

Why would elves write spells in dwarvish?

Quote from MaximusCathril>>

But this particular icing is cardboard flavored, and I happen to not enjoy that. 

 No. Just no. Maybe ... greater GM control comes from giving the GM tools to micromanage every aspect of the game. But the GM already has full control of what spells are available, so that point just becomes moot. The rule about spellbooks has zero impact on balance.

Quote from MaximusCathril>>

It's literally the exact opposite: Avoiding making life harder for no reason.

Yea but why? Busywork has no inherent upside to me.

I'm not sure what you're saying here. The imaginary casters need imaginary exercise for which reason, exactly? Are you saying that ... I dunno, combat is so easy for a caster, so attaining their core class thing needs to be hard?