Just watched the new X-Men movie for the first time. In it they showed a mutant who could create dimensional portals, which is certainly a very mage like ability if transferred into D&D or Elder Scrolls, wouldn't you say? Well, it got me thinking, what school of magic would such an ability belong to? I've pinned it down to either Alteration (because of the manipulation of the natural environment) or Conjuration (because you're creating a portal like you would a creature or object). My guess is that it's leaning more on the Alteration side of things.

The teleportation spells back in Morrowind (Almsivi/Divine Intervention, Mark and Recall) were classified as Mysticism, but opening portals to other realms would be classified as Conjuration.

That said, the schools of magic are an arbitrary system that are dictated by gameplay more than anything.

Mysticism for sure, although I'm not sure teleporting is the same as opening a portal - I presume with a portal, more than just yourself can go through it.

Mysticism is the manipulation of the world's magical energies. Alteration is the manipulation of physical properties or laws, so there's some overlap.

I think he means portals in the scene of the portal games. like I make a portal on the wall and my head comes out the floor

Along side Morrowind's own Divine Intervention/Mark and Recall, you can find a couple of mages who teleport around during combat, namely Orchendor and Vals Varen. A hagraven at Hag's End also ports around her temple.

But other then that, yeah, the Schools are constantly subject to political whims and and a institutions personal categorization. I'd reach for Mysticism first and foremost though.

I get reminded of the Psijics whenever I think of this sort of thing. For the sake of brevity, I'll simply say one of the reasons I think of them is because of the fact they can make the entirety of Artaeum disappear at will during tumultuous periods of history.

Not sure if "disappear" should be read as "rendered invisible" or "displaced."

Given that the Thalmor can't seem to find hide nor hair of them, I'm guessing the place is just gone. Displacing time to the point that other skilled mages (Tolfdir picks up on it, but has no idea what it was) around them, sending astral projections of themselves, and being skilled enough to contain something like a destabilized Eye are a testament to their prowess.

That and the College presumably teleported the Eye to its own hall as well, but those guys probably have everyone beat in the sheer scale they can pull it off.

I'm sure one potentially could portal around like Blink, but I bet it would take far to much magkia to be practical. Besides, haven't anyone played the one amulet quest line in Skyrim? You encounter a few lich's who teleport about like Nightcrawler, but mainly portals are something used in magical constructs like the Oblivion Gates and the Falmer ones in Dawn Guard and not something you see people casting.

What school of magic would create something like the Falmer magical doorways?

Mages in ESO are opening portals all the time. Mainly to get the player easily back to civilization after a long quest.

@OP: Why so obsessed with the schools anyways? Mysticism, Conjuration, take your pick. The Falmer, which build these wayshrines, didn't have such a categorization.

Can even snap their fingers and have someone from the other side of that lava river appear next to them safe and sound.

For RP reasons. I want to know what kind of mage from what school could create similar portals.

The schools of magic are nothing but a philosophy created to help new mages understand what you can do with magic, it's not something that's set in stone magicka works like this. If you know how you can do near anything.

I'm going to guess that old magic like the Wayshrines and paragon portals are something that don't fall elusively under any specific school.

If you must put it into a school I'd put it under Mysticism since the teleport spell in Morrowind was under it.

What I'm wondering is if teleportation spells are even the same as portal spells. Portals are magical doors between two realms, e.g. Wayshrines and Oblivion Gates. Recall/Intervention spells simply teleport the caster - if they were portals I would assume they'd be able to take more than just one person through.

The question really is... how do both work? By warping spacetime? Then I would say it's Alteration-esque.

Oblivion Portals surely need Conjuration.

Do portals transporting people from one point in the same realm (say Mundus) to the other involve an extradimensional medium (Oblivion/Aetherius/Outer Realms) or do they just transcend normal spacetime by literally warping it?

We know there is some kind of "Brane-Space" in TES, which links Tamrielic metaphysics to modern Quantum theory.

I believe portals and teleportation work like wormholes and quantum teleportation (Mark and Recall could be seen as a form of practical Quantum Entanglement).

But what is the unifiying force in Tamriel? Gravity is supposedly eleventh-dimensional in our reality. Is Magicka hyperdimensional? Creatia?

The universe is 3+ dimensional. The excess dimensions are probably mostly occupied by the Waters of Oblivion but the Princes can shift their planes along them to bring them closer/further to Mundus. Teleportation is taking a shortcut through these higher order dimensions.

Navigation to a safe exit point is an issue unless you use known landmarks (the planes belonging to the Princes being somewhat fixed provide these), or some form of extradimensional beacon (akin to the http://www.uesp.net/wiki/Shivering:The_Helpless_Army#All.27s_Not_Well_at_the_Wellspring provided by Sheogorath to his servants) like an altar to some sufficient divinity or a Mages Guild teleportation services expert, or a Mark a skilled mage has prepared for themselves. This is why the exit point is fixed for most forms of teleportation with only navigating through the Princes' realms allowing some degree of arbitrariness.