Chaosmancer
Legend
Here, "Necromancy" is the "darkside" of astral thought and ethereal spirit, relating to the Negative Void rather than the Positive Energy. It is mainly a category to represent the reallife thematic tropes of "necromancy" and "black magic", and is intentionally multischool for a specific genre.
If you find it annoying to separate out Necromancy in this thematic way, I am fine with just making: Conjuration be "Astral Plane with Celestial, Fiend, and Aberration", and Dunomancy be "Ethereal Plane with Fey and Shadow".
But for the sake of organizing popular themes, it can be worthwhile to silo the darkside themes into Necromancy, similar to how Warlock is a go-to for darkside magic themes − generally with effects done by dangerous and evil spirits.
I do find it annoying, because it ignores thematics within the game. Necromancy is often associated with necrotic damage, and spells like chill touch or Toll of the Dead. If you make it the "evil darkside of magic" then what do you do with the Spore Druid who deals necrotic damage and makes a zombie servant? Are they automatically evil and dark, associated with fiends and aberrations from beyond the stars?
I don't think so. That doesn't make a lot of sense.
I don't want ANY morality to be in the magic, because it is hard to justify it. Even Enchantment which I strongly feel has many negative thematics... also has spells like Zone of Truth, Bless, and Hold Person which I cannot say are evil spells.
Even saying something like "the void is evil" ignores other conceptions of the universe and morality. The Void in Shinto religions is not a force of evil. So why enforce that upon the game?
Dunomancy is the stuff of ethereal forces, including gravity and telekinesis, and including the spirit world of the Fey (and Shadow).
Divination is space-time, including seeing across space and time during precognition, traveling across space during teleportation, and traveling across time during time travel or other chronomancy effects.
Yes, the Dunomancy such as gravitational force and the Divination such as space-time are separate areas of specialization because the storytelling tropes are so different from each other. If you want a mage with a more scientific flavor, who understands how both fundamentally interrelate, then choose spells from both the Dunomancy and Divination schools.
Depends on the story-telling. Most stories that feature prophecies and precognition often don't involve gravity manipulation. Those that involve telekinesis... actually often involve precognition and telepathy, all as the same power. I've even seen psychic teleportation.
So, it matters deeply which stories you are trying to emulate, because reading people's minds, looking into the future, and throwing people around or setting them on fire can all be the exact same power source in the right sort of fiction.
Illusion is often made out transient ether, namely a construct of "force" and "magical energy", that behaves virtually as if matter but isnt actually matter. Compare the holodeck of Star Trek. However some illusions involve the alteration of reality itself, a blurriness between subjective reality and objective reality, and result in real matter and actual reality. The concept of manifesting illusion is distinctive enough in stories, and distinctive enough mechanically as statting the objects themselves, to merit its own school specialization. Consider, most stories about mages who create illusions (force constructs) dont necessarily have them be able to fly (dunomancy telekinesis and gravity). They are different themes.
It also depends on how you are creating the illusions, ie, are you manipulating light or perception. But more importantly, the point was that Fey are well known for illusions, and Dunomacny was ethereal... but then illusion was ethereal matter. Giving manipulated light a physicality can even be gravity magic.
But then again, you are correct, illusions are often seen as distinct and make sense as a field of study.
I think this is largely just a failure of the idea of making specific sections of cosmology specific types of magic. It simply doesn't work. The Feywild can be full of a dozen different types of magic, so trying to narrow it to one specialization doesn't work.
Elemental Planes can easily have Evocation responsible for Earth effects as well as the rest of the elements Air, Water, and Fire. However, so far in D&D, earth effects are consistently Transmutation. I can see the logic of linking Transmutation with Earth, Plant, Beast, thus aspects of the Material Plane generally. In this context, Plant and Beast are creatures made out of solid matter. I have made peace with how D&D separates the Earth Element from the other three "energy" Elements.
You can make peace with it, but that doesn't mean it isn't without flaw. There is logic both ways.
Most magic weapons are Divination in the sense of being "lucky". But some magic weapons might be Dunomancy relating to telekinetic aim or whatever. Really any school of magic can have its own rationale for why a weapon is more accurate and deals more damage. It depends on the flavor of the magic.
Consider weaponlike spells: Elemental Weapon is Evocation inflicting elemental energy damage, Magic Weapon is Divination being lucky.
Spiritual Weapon is tricky, some aspects are Illusion in the sense of a quasi-real force construct, but it actually deals Force damage and doesnt behave like an actual weapon would. Mainly the Force damage makes it a force effect of Dunomancy. If the quasi-real object dealt weapon damage (Pierce, Slash, Bludgeon), it would be fully an Illusion.
Some spells cover the concept of one school, but the way that the spell description is actually worded makes it belong to an other school. For example, Mage Armor generally the covers the idea of force armor that repels attacks thus would be Dunomancy, but is actually written to be more like a quasi-real Illusion.
There is no way that being lucky allows a weapon to cut what it otherwise cannot cut. That is a function of being a magical item, not a lucky item.
But you are getting to my point, this a all messy and confusing and could go in multiple different directions. The more tightly you try and define "this magic means this" the more you are going to find those edge cases that don't make sense or challenge the entire structure you have built.
DnD's current system being very loosely defined is a strength here, because it largely... doesn't matter.