How does Summoning corporeal work in The Elder scrolls

[Ushakanta]

I can easily infer how summoning Daedra works (using Magicka to draw forth and bind a Daedra while simultaneously forcing it to take physical shape on Mundus) and even how summoning ghosts works (drawing forth lost souls from Oblivion or calling them down from Aetherius for assistance) but is it ever explained in any lore how summoning corporeal undead (skeletons, zombies, etc.) works? Does the caster shape their bodies out of raw Magicka or are there rotting legions somewhere that the caster teleports the bodies from?

[Isabella]

I forget which plane but I was certain there was one that had undead roaming around that could've been a possible source for undead summoning. This seemed valid to me since necromancers both had permanent undead hanging around and summoned ones as well. Then there's the game mechanics view and like proweler said in Morrowind an Orc says she'll teach you a Necromancy spell and it comes in the form of summon undead. Any explanation works for me since there's enough sense in whatever's right, but there's only one thing that really bothers me and has bothered me ever since the first time I witnessed it.

[Bricklayer]

Where would you get a lich from? If a lich dies in combat did you just 'port in some random magisterial who's life is now over because you were playing around with the Gatekeeper? The only reason so far that seems plausible is that master conjurers can forcefully summon liches to them because they're now a type of undead and can't resist for long, and hopefully no one gets the idea to start killing off every lich that is summoned to rid the world of them. It still doesn't sit right with me I'd rather that spell not be in Oblivion at all unless there's something I'm missing that justifies being able to summon what looks like a lich and how this doesn't become a problem in the Elder Scrolls world.

[Defender14]

The skill conjuration in my opinion is just an over-simplification of several of similar magical arts. You call it all conjuration because fundamentally thats what you’re doing in each case, that and it would be kind of absurd to have Necromancy, Daedric Summoning, and Misc. Summoning for individual skills. Bethesda thinks about the big picture and the big picture is it's easier for them and us to simplify such things.

[Rily]

I recall reading a text in the Imperial Library about just such a thing. Daedra come from the plane of Oblivion, they are summoned through conjuration and their animus is used a blueprint for their physical form on this plane, Though as we all know in Oblivion were the Daedra's Animus remains is where it would be strongest but having been for lack better terminology Teleported/cloned into Mundus it is weaker. A lot like taking a beer and pouring part of that beer into a different glass then filling the rest up with water. Thus it is one capability that conjuration possess is to bring forth Daedra from Oblivion.

[Messenger]

Well according to me necromancy is another capability of the skill we have come to know as Conjuration. Summoning ghosts and what not is simply calling forth a spirit from the ethereal plane and binding it's existence to Mundus. Now theoretically summoning a skeleton is not as difficult as one would think, calling forth a spirit from the ethereal plane and producing a physical form for it can either be a product of the skill of one's power in creating things from nothing or simply making a full skeleton pop from one place to another as a vessel to hold the newly bound soul.