The availability of certain spell is restricted. As a general rule of tumb, spell from the PHB are not restricted and are all generally available, although some exception may exist with spell such as Wish or Miracle.
There are 4 categories of spells: Common, Uncommon, Rare and Very Rare.
The rarity is determined by the book from which the spell is originated. If the spell is in more than one source, then the source the most available to the PC should be used, EX. A spell is in the PHB but also in the Forgotten Realm Campaign setting. Although the later is more up to date, we may use the more updated version but the rarity will still be based on the PHB, so it will remain a common spell.
General rarity from book (rule of thumb):
Uncommon: Spell Compendium, Player handbook II
Rare: Class book, Race books, monster manual and similar
Very Rare: Campagin Settings, Vile darkness and similar books, any other reference.
Some rarity are subjective to the spell at hand and may not fit 100% in the classification above.
There is a “cost” factor associated with the rarity when buying and selling spells either from a spellbook, scroll, potions and others means that I don’t know. Generally speaking this should really affect spellbook, scrolls both arcane and divine, potions, wand and all will nto be affected as it is way to cumbersom to calculate.
Very Rare: 6.0
This only applies to buying and selling, not scribing spells…
This means a spell value in a spell book would be worth per page:
Common: 100 gp
Uncommon: 150 gp
Rare: 300 gp
Very Rare: 600 gp
So a very rare spell of 1st level would be 600gp while a 5th level one would be 3000gp.
Now that we have check the concepts behind availability of spells and their rarity, it is easy to say that a spell caster wold know all the spells. This is not true. The spell knowledge is based on a DC 10 spell craft check by comparing the results with the table below. Having a result equal or higher that the DC outline the table means that the spell caster as knowledge of the spells in that category and therefore can select them as spells on their spells list or add them to their spell book (assuming a wizard exits) when gaining new spells or the opportunity present itself.
As spell caster is always assumed to know at least the common spell of a level of spell he can cast even if he does not meet the take 10 DC of that level.
Prognoze the Mage is a level 7 caster. He as a spellcraft modifier of +15 (10 ranks, +3 int, +2 special bonus). His Take 10 check is therefore 25.
From the table below, since his check 25, he as knowledge of all the following spells:
Common Spells: From level 0 to level 5
Uncommon Spells: From level 0 to level 3
Rare Spells: From level 0 to level 2
Very Rare Spells: Nothing…
This means he can chose (when possible) any spell in that spell bassin when he can select new spells.
|Spell Level||Common Spell||Uncommon Spell||Rare Spell||Very Rare Spell|
This information does not change the fact that to identify a spell effect you still need the spell craft check to be done. This is merely theoric spell knowledge.