Question about spells known.

[Mystic Muse]

If a wizard were to have their Spellbook dispelled (Or otherwise lose it in some way) would they also lose all spells known or would they keep those in spite of having lost their book?

[Drakevarg]

Other than cantrips, probably.

Would dispelling work on a spellbook? I thought they were literally just written down like mathematical formulae.

[Biffoniacus_Furiou]

Once you make the Spellcraft check to understand a spell, it is effectively considered a spell you know even if you never bother to put it into your spellbook. Losing your spellbook means you cannot prepare most of your spells any longer, but you never have to make the check to understand those same spells again.

For example, if you have the Spontaneous Divination ACF from Complete Champion you can read a divination spell and make the spellcraft check to understand it, and forever be able to spontaneously cast it even if you never put it into your spellbook. The book is what determines what spells you can prepare, but reading a spell and making the check to understand it is what determines if you know the spell and that can never be taken away.

[Rannil]

If a wizard were to have their Spellbook dispelled (Or otherwise lose it in some way) would they also lose all spells known or would they keep those in spite of having lost their book?

If you mean with "spells known" prepared spells: yes as long as you don't sleep eight hours in a night. The rules aren't that clear on it but you need to re-prepare after eight hours of sleep, so if you sleep seven hours you keep spells known from the previous.
If you mean the spells you gained at each level: you lose them, but I vaguely remember some kind of wis/int roll that gave you a chance to remember some of your spells.
If you mean that you gained something like "spells known" as sorcerer/bard then those you would also remember always.

Edit:

Once you make the Spellcraft check to understand a spell, it is effectively considered a spell you know even if you never bother to put it into your spellbook. Losing your spellbook means you cannot prepare most of your spells any longer, but you never have to make the check to understand those same spells again.

Sort off true, sort off isn't true.

If you loose your spellbook and try to replace it you can put any prepared spells in it, but it will cost the daily cast of that spell.
You can prepare the spells you know from a other mage's spellbook, but you need to make a Spellcraft check. (And then write them in your new spellbook)

So you don't forget the spells, but if you want to write them back and need to prepare the spells from another mage's spellbook (or from a scroll) you do need to make a new spellcraft check.
Spell already prepared can be written back without any checks, just ink costs.

[Another_Poet]

If a wizard were to have their Spellbook dispelled

A spellbook can't be dispelled. It is not magical in and of itself, it is just a book with writing in it. If they have put wards on the spellbook (Secret Page, etc.) those can be dispelled. But the book is just a book, which they refer to when preparing their spells.

(Or otherwise lose it in some way) would they also lose all spells known or would they keep those in spite of having lost their book?

Correct, it if is stolen or destroyed they cannot prepare any more spells except for Read Magic. A wizard can always prepare Read Magic even without a spellbook. However, any spells they already prepared before losing it, they can still cast (but once they cast them they're gone!). if they are smart they will scribe all their remaining prepared spells, thus effectively starting a new spellbook, but this will take weeks.

For bonus points, sunder their spell component pouch too, so they can't even cast most of their prepared spells at you as you run off with their spellbook :)

[Lord Vukodlak]

Rannil slight mistake in your knowledge of spell preparation.

A prepared spell remains prepared until cast, If you rest for 8 hours you don't lose any previously prepared spells but you could prepare a new set of spells.

If my gnome illusionist prepares a full complement of spells. But doesn't cast a single one for a week, he can still cast his full complement of spells. Even if due to insomnia he hasn't slept for a week.

A spellbook is basically a wizards soul, unless he keeps a backup. Destroying it is a fate worse then death. Really losing a level is less painful then an entire spellbook.

For high level casters keep a scroll of wish around. Should your spellbook be destroyed and your backup isn't enough. You can wish your book back.

[2xMachina]

Always have spare books. 1 in a safe place, and 1 for adventuring.

[Drakevarg]

Always have spare books. 1 in a safe place, and 1 for adventuring.

Of course, if you habitually go on far-flung adventurers, this could render your backup spellbook horribly out-of-date.

[Rannil]

Rannil slight mistake in your knowledge of spell preparation.

A prepared spell remains prepared until cast, If you rest for 8 hours you don't lose any previously prepared spells but you could prepare a new set of spells.

True. My mistake. You need to clear your mind, by sleeping for at least eight hours, and I thought that "clearing" your mind also wiped away previous prepared spells.
I double checked it the PH, it clearly states " Once a wizard prepares a spell, it remains in her mind as a nearly cast spell until she uses the prescribed components to complete and trigger it or until she abandons it. "

[ScionoftheVoid]

As mentioned the book can't be lost through dispelling (it's just normal writing inside), but what happens if you lose your spellbook is, IIRC:

You keep all your prepared spells prepared until they are cast.

You can prepare Read Magic or any spell you have the Spell Mastery feat for as normal but cannot prepare any other spell (not even one you still have prepared).

Any spells that you know, but don't have prepared, you have to find and reassemble in a new spellbook.

Any spells that you know and have prepared, AFAIK, you need to do the same for.


This is why it is always a good idea to have a spare book or two with your basic spells, updating them as necessary. Preparing at least one with Drawmij's Instant Summons (through a scroll if necessary) is an excellent strategy as soon as it is affordable.