What character class?
A sorcerer at 1st level can cast 3 first level spells per day (plus bonus spells for high charisma). They know four 0 level and two 1st level spells. They can cast the 0 level spells as often as they want. They can cast any combination of the first level spells they know 3 times.
There are two types of spellcasting in Pathfinder. Prepared spellcasting and spontaneous spellcasting.
Wizards, clerics, druids, and witches prepare spells. At the beginning of a day, they chose from their spell lists or spellbooks what spells they want to have ready for this day. When they cast the spells, they can not use them again until the next day and they prepare them again.
Sorcerers, bards, and oracles don't prepare spells. They have a limited list of spells they know, but they can cast them without having to chose which spell goes into which slot at the beginning of the day. When a sorcerer knows the spell fireball, he can decide at any point that he wants to use one of his 3rd level spell slots and cast the fireball spell.
If a wizard has the fireball spell in his spellbook, he has to prepare that spell in one of his 3rd level spell slots in the morning. He can not decide later in the day that he wants to cast another fireball and use an empty spell slot for that.
Basically, wizards have to put the spell into the slot in the morning, but sorcerers can put the spell into the slot right at the moment they want to cast it. On the downside, sorcerers have a much smaller list of spells that they know, while wizards can have basically every spell there is in their books.
If a wizard has the fireball spell in his spellbook, he has to prepare that spell in one of his 3rd level spell slots in the morning. He can not decide later in the day that he wants to cast another fireball and use an empty spell slot for that.
Actually...
You're largely correct, but a Wizard can leave a spell slot "open" and prepare a spell for that slot at some later point of the day. It has to be a not-yet-used slot, and it takes quite some time. But it can be done.| 1 person marked this as a favorite. |
A concrete example:
I'm a first-level wizard (universalist school) with 16 Intelligence.
According to the table "Spells per Day" in the class description for wizard, I get three 0th-level spells and one 1st-level spell per day. That means that I can prepare three spells from the 0th-level spells in my spellbook and one spell from the 1st-level spells in my spellbook. Once they're prepared, I can cast each spell I've prepared once. In the case of 0th-level spells, there is an additional bonus: I can cast 0th-level spells over and over again so long as I have that spell prepared. In the case of the 1st-level spell, I can only cast it once before the spell slot is "used up" for the day.
But wait, I have 16 Intelligence! Looking at the Ability Modifiers and Bonus Spells table in the section on Ability Scores, I see that since I have 16 in the wizard's primary casting stat, I can prepare one more 1st-level spell per day. This can be the same spell as the other 1st-level slot or a different spell. If I prepare the same spell, I'd be able to cast that spell twice, "using up" a slot each time.
So, I can prepare three 0th-level spells (which I can cast as many times as I like) and two 1st-level spells (which I can cast once each, using up the slot as I cast). If I want to refresh those slots I used up, I have to wait until the next day, when I can prepare spells in those slots. I also have to sleep (mostly) for 8 hours before preparing those spells. Preparing all of my spells takes 1 hour, but if I only used up some of my slots yesterday, it takes less time, but always at least 15 minutes. If I don't do these things, I can't refresh my spells, but I can still cast any spells that I still have prepared from the previous day.
What if I don't know what 1st-level spell to prepare that day? Well, I can choose not to prepare one of those slots. That slot is not "used up", but it doesn't have a spell in it either. Later on, when I come across a situation that requires one of the spells in my spellbook, I can stop and prepare that spell in the open slot. That would take at least 15 minutes. (The exact time is a little fuzzy going by CRB alone.)
That's basically it.