I'm DMing for a group that has a player who is an eldritch knight level 7 and wants to multiclass into wizard to expand his spellcasting abilities. The short version of my question is as given in the title and I'd think is ultimately based on two factors
- When do you get access to 3rd level spell slots as an Eldritch Knight 7/Wizard X?
- When can you cast 3rd level spells as a multiclassed character?
First, spell slots: This seems the easier question of the two and is outlined fairly clearly in the PHB p.164
You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels (rounded down) if you have the Eldritch Knight or the Arcane Trickster feature. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.
And the table is given as (again on p.164)
MULTICLASS SPELLCASTER: SPELL SLOTS PER SPELL LEVEL LvL. 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 1st 2 2nd 3 3rd 4 2 4th 4 3 5th 4 3 2 6th 4 3 3
So, for an Eldritch Knight level 7, that's 7/3 = 2 (rounded down). Each level of wizard would give a full level for the table, so Eldritch 7/ Wizard 1 = table row 3, Eldritch 7/Wizard 2 = row 4, Eldritch 7/Wizard 3 = row 5 (to hit 3rd level spell slots).
The 2nd question of "when can you cast a 3rd level spell in this situation?" doesn't seem to be directly answered by the spell slots table and the best/nearest answer I can find is found above the spell slot section on PHB. 164:
You determine what spells you know and can prepare for each class individually, as if you were a single classed member of that class.
So, taking this pretty much verbatim, from his 7 levels of Eldritch knight he'd have his same 2 cantrips, 5 spells known, 4 first level and 2 2nd level spells from his 7 levels of that class (PHB p.75). Wizard has it's own table but for the sake of brevity, doesn't give access to/spell slots for 3rd level spells until 5th level. So, my understanding is that he'd need to be an Eldritch Knight 7/Wizard 5 before he could pull off the desired "Action Surge Double Fireball" turn.
That seems to be the answer from looking online and a literal reading of the PHB but that would mean that he'd have, in theory at Eldritch 7/Wizard 3 for instance, as given above based on the table, 3rd level spell slots that... he couldn't use for 3rd level spells. The PHB does seem to support this as a possibility by saying (PHB p.164):
If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your lower level spells. If a lower level spell that you cast, like burning bands, has an enhanced effect when cast using a higher level slot, you can use the enhanced effect, even though you don't have any spells of that higher level.
For example, if you are the aforementioned ranger 4/wizard 3, you count as a 5th-level character when determining your spell slots: you have four Ist level slots, three 2nd level slots, and two 3rd level slots. However, you don't know any 3rd level spells, nor do you know any 2nd-level ranger spells. You can use the spell slots of those levels to cast the spells you do know-and potentially enhance their effects.
Is that correct? My personal opinion is that's a rather long time (12 being near the end of many campaigns) and kind of lame, but I try to go by the book for the most part.
So, please tell me if any of the above is incorrect or if there's something I've overlooked. Thanks for your time and apologies for any formatting errors.