Where is the explicit rule that states a wizard must have an appropriate spell slot to prepare a spell?
Asked another way: Can a wizard prepare a spell he does not have a spell slot for?
I am having trouble finding the explicit rule that states a wizard must have the appropriate spell slot available to prepare a spell he knows.
I am aware that preparing a spell one cannot cast is potentially a pointless exercise, but it does have some potential implications when it comes to item creation. Before going down that rabbit hole - I could use some help finding the exact rule or rules governing this mechanic.
To learn, prepare, or cast a spell, the wizard must have an Intelligence score equal to at least 10 + the spell level. The Difficulty Class for a saving throw against a wizard’s spell is 10 + the spell level + the wizard’s Intelligence modifier.
This clearly states that learning (knowing), preparing, and casting spells are three separate mechanics. And does not state the wizard must have an appropriate spell level slot in order to add it to their spell book - and thus know the spell.
You can cast a spell at a lower caster level than normal, but the caster level you choose must be high enough for you to cast the spell in question, and all level-dependent features must be based on the same caster level.
This mechanic ties casting the spell to a minimum caster level. But does not explicitly state or exclude preparing the spell at an even lower caster level - just that you wouldn't be able to cast it. Leading one to believe it could be possible to prepare a spell (but not cast it) if one does not have enough caster levels.
Spell Slots The various character class tables show how many spells of each level a character can cast per day. These openings for daily spells are called spell slots. A spellcaster always has the option to fill a higher-level spell slot with a lower-level spell. A spellcaster who lacks a high enough ability score to cast spells that would otherwise be his or her due still gets the slots but must fill them with spells of lower level.
Again - only mentioning that slots are needed to be filled in order to cast a spell. Leading me to believe it is implied - but not explicit - that one can prepare a spell - but not cast it - if placed in an inappropriate slot.
So the question stands: What and where is the rule that explicitly ties spells preparation to spell slots?
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