Okay, so I just found it on my PC, and I thought it was finished enough to 'publish' on the forums.

There are several types of undead, of which they are the two most common types: the 'zombie' and the 'ghost'. It is commonly accepted that the zombie is a body with no soul, and the ghost is a soul with no body. Let us now study a very, very special example of undead. One that doesn't fit any of these categories.

The Lich.

We don't know much about these, except that they use magicka to lengthen their lives, that, to become a lich, they must temporarily transfer their soul to a soul container, and that, from Daggerfall to Oblivion, these odd magicians have become surprisingly weaker. Now, with as only sources the information we have, a bit of biological knowledge and logics, I will try to deepen the knowledge we have.

Obviously, their brain and nerve system are still intact, as else they couldn't think and move, right? But, me thinks, most of their other organs should be decomposed- they breathe very difficultly, and their body decomposes as well, which is a signal of organs sustaining the body not working- this would include lungs and heart.

But, if they don't have those, where do they get the energy to actually do things? Well, we already know they use magicka to lengthen their lives. So what is my conclusion? Magicka. They get their energy almost straight from Aetherius. I think that, to become a Lich, one must transfer their soul to said object, after which they die. Because of how close the object is to the corpse, the soul will flow back into the body, reactivating only the brain. Either the person in question will endlessly suffer in a corpse, or they will find their way into magicka and get up again, reborn as a Lich. Due to the lack of needed substances supplied by blood, their body will decompose.

I know it probably doesn't make any sense at all, but I wanted to know what you think of it.

I've killed enough liches to see form my self that they are nothing but bones and the rags of what they used to wear when they still lived that and a lack of brain and nervous system doesn't seem to bother most skeleton warriors either.

Another qeustion, how does one get magicka straight from Aetherius?

Well, I assumed that the Magicka inherent in Mundus comes from Aetherius (which makes sense), so it's just a shorter way to say

I said it didn't make sense.

Well the lack of life in a lich stops them from appearing out of nowhere?, Taking lots of blows from gigantic axes, and lets not forget summoning giant skeletons...

Well, we all know a strong mage can teleport himself to Aetherius for as long as they want to. They must be doing something fun while they're there, why not fill a backpack full of magic?

I'm mostly kidding of course, I haven't seen those mages come back. If they did, they must be hiding somewhere quietly.

I've heard of this with Oblivion, did I miss something about Aetherius somewhere???

It was a common Mages Guild mission in Daggerfall, where you had to protect a mage during his three-hour trance at the end of which he'd be teleported into Aetherius.

Liches have been present since Arena. They were pretty strong back then.