Does Arcane Disciple give the Nar Demonbinder a 1st-level spell slot?

Question

A player wants to be an Ultimate Magus. He has poured through the forums, and I have as well to know what [we] are getting into. He wants to be a Wizard / Nar Demonbinder / Ultimate Magus.

The forums say to take Arcane Disciple to get 1st level spontaneous caster spells. The text of Arcane Disciple states you add such and such spells to your list and you can cast them using your Wisdom for the spellcasting purposes.

However, I disagree with what the forums are stating allowing Nar Demonbinder to allow one to qualify for Ultimate Magus:

At first glance it appears you can’t enter UM with Nar Demonbinder since it first level only gives you 4th and 5th level spell slots with spells you must select from a specialized list, and this list has no 1st level spells. Thus by itself you can’t cast 1st level spells and no UM for you :( . But this all changes with a feat that grants spells, such as Arcane Disciple or Mother Cyst.

The spell slots are simply not there to allow 1st level casting.

I explained to the player, if an 18th level Bard took Arcane Disciple, he doesn't have the spellcasting slots to cast his 7th+ level spells that the feat would give you.

Am I wrong? He is insisting the forums would not have stated otherwise. I have never known, nor have I personally, tried this class combination/prestige class before. I told him I would consult RPG.SE before giving him a definitive answer.

I stressed the point that I believe I am correct. But I have been wrong before, and I like to give my players the benefit of the doubt.

Answer 1

Arcane Disciple doesn’t let you cast spells of any level you couldn’t otherwise

You may learn these spells as normal for your class

The nar demonbinder does not normally learn any 1st-level spells. Arcane Disciple does not give you free spells known, it just adds them to your spell list so that you can select them as normal.

I suppose one could argue that you could use one of your 4th-level spells known to learn a 1st-level spell using Arcane Disciple. Note, however, that the nar demonbinder learns spells as a sorcerer does, and the sorcerer class says nothing about being able to choose a spell known lower than the slot indicated by the table. Note that the rules about spell casting explicitly state that you can cast spells in higher-level spell slots. Without a similar statement for learning spells, I don’t believe you can. So my conclusion here is that this does not work, by RAW.

Mother Cyst does work, however

Mother Cyst adds the spells from the feat as spells known. Thus, the nar demonbinder can cast the lower-leveled ones from his 4th-level spell slots, since casting (unlike learning) has a statement that you can use higher-level-than-necessary spell slots to cast them.

This does not work for higher-than-normal slots, as in your bard example, because you still need a slot that can cast the spell. Your bard might “know” necrotic tumor on some level, but a 6th-level slot cannot cast a 7th-level spell. The nar demonbinder’s 4th-level slot can cast the 1st-level necrotic awareness.

This is all unnecessary anyway

Prerequisites are always stated as minimums. Looking at the Mother Cyst feat itself, it requires “Caster Level 1st” – this in no way disqualifies those with higher caster levels. The ability to cast 4th-level spells is better than, and qualifies as, the ability to cast 1st-level spells.

Note that some feats are exceptions here, and use particular wording. Numerous feats have a requirement of “1st level only” – unlike Leadership, which just says “character level 6th.” Not only 6th, just a minimum of 6th.

Answer 2

I've got three points that I think are relevant here.

Most D&D forums abuse rules, especially char-op ones.

This kind of rules loophole abuse is pretty common on boards where people give character advice. The point of most of these builds is to give you as much power as possible while giving up nothing. The Nar Demonbinder is a pretty decent class on it's own, butusing Ultimate Magus to get full Demonbinder casting while losing very little from the Wizard side is pretty ridiculous. If you're uncomfortable with this kind of rules abuse, you should probably suggest that your player doesn't take advice from optimization boards like this.

I mean, he's a full caster. If you're a full wizard or sorcerer, you're already one of the most powerful classes in the game. As an Ultimate Magus, you lose out on your highest level spell slots to effectively gain more spells than you can ever cast, and more versatility than you'll ever need. Even playing it the way it was intended will make you more powerful than most other classes.

Their interpretation is, by RAW, correct.

You're right that the Demonbinder doesn't get any lower-level spell slots, but that doesn't mean that they can't cast lower-level spells. You can cast a lower-level spell using a higher-level spell slot. If a sorcerer knows magic missile but only has 4th level spell slots open, he can still cast that magic missile using his 4th level spell slot. In the same way, a Nar Demonbinder who somehow gets 1st level spells on their list can cast them using his 5th level spell slots.

The rules on spell slots say:

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.

When the Nar Demonbinder gains new spells known, it would make sense that they could choose to learn a lower-level spell than their new spell level calls for, and thus learn the new 1st level spell that they gained from Arcane Disciple. Alternately, they could use Extra Spell to gain that new spell, instead.

You're the DM. If you think a particular combo isn't okay, then you can disallow it.

If you really don't like your player using this combo, then just say it. It's totally reasonable to say to a player, "Hey, I'm not comfortable with you using the Nar Demonbinder to qualify for Ultimate Magus. It might be technically correct by the rules, but I feel it violates the spirit of that prerequisite, and so I'm disallowing it."