My friend and I are in disagreement over how the rules work, yet we can't seem to find anything to accurately answer the question.
Let's say I have a 1st level Wizard, which has a default of 1 first-level spell per day. Let's also say that the Wizard has an 18 in INT, which grants him one bonus 1st, 2nd, 3rd, and 4th level spell slot.
My friend says that it's within the rules to prepare 1st level spells using those bonus 2nd, 3rd, and 4th level spell slots.
I say that I can't, because I can't cast 2nd, 3rd, or 4th level spells yet and don't have access to those bonus spell slots yet.
Which of is right?
In addition to having a high ability score, a spellcaster must be of a high enough class level to be able to cast spells of a given spell level.
You don't get bonus slots for a level until you have regular slots of that level.
The only exception is classes with a "0" written for a given level of spells (like a 4th-level Paladin or Ranger). Those classes only get to cast spells at those levels if they have an appropriate bonus slot.