So that they can live forever in them and have lots of children without worrying about population concerns. Also because it's not a super good idea to drop tons of lifeforce on people who know sorcery but just a little.

They are very in favor of having lots of children. Someone observes that a fixed number of planets won't suffice for that.

No but a large number of them plus living for a very long time and lots and lots of magic should be enough for them to become self-sufficient before that becomes a problem.

Can they do the planet-finding thing as well?

They cannot; it's done using a magical artefact whose origin he does not know and whose properties he cannot replicate.

(A way to circumvent the terrible placement of doors occurs to him. He'll inform Aitim of it later.)

How common are those? Are they products of the same magic system?

The key's not a product of the same magic system, no, it was literally lying around in his world somewhere and his world's magic probably shouldn't have been able to produce it. And he has some other artefacts that weren't produced by sorcery—the ring of translation he's currently using so everyone here understands him in their native language is one.

How do they get those?

Those he purchased in another world.

How do they get to other worlds?

He'll open doors to them, after he finds them.

Can they get to the worlds he came from?

Not easily. Doors are—not exactly one-way, while they're open they're two way, but when they close they can only be reopened from the universe they opened from in the first place, and creating a new door where the previous one used to be doesn't lead back there so he'd have to scour this universe to find the specific door that leads back to the previous world, and the previous one, and so on.

And he, er, bought this ring several hundred years and worlds ago.

Wow. Can he tell them about all the worlds he's been to?

...well yeah actually but do they prefer to be told about that rather than learn more magic?

No.

He thought so.

So here's how to introspect on the aspects, and meditation is an extension of it. If they do it for long enough they'll start getting subjective impressions of where lifeforce goes and how to put it in different places and move it around, and an extension of that will be conversion between aspects but they definitely won't get that today. Normally an instructor would share some breath with their students to help with the first introspective exercises but he has none, so he'll compensate for that by giving them some extra health, which is a very noticeable feeling to the extent any of them were in less than perfect health—a cold, a sore throat, a contusion.

And once they get the basics he can start teaching them about the school of magic in more detail. They can suggest some designs of magical effects and he'll teach them how to tell how much they would cost and how to change them to be more efficient. They might also notice that health and youth effects are comparatively harder and more expensive than breath, stamina, and wakefulness ones.

(Which is by design—cleaning magic of the kind that would suffice to replace reds is definitely health magic and he's not making that easy on them. Not that he's telling them this.)

They ask if that's universal. 

It's not; each school of magic sacrifices some things to be better at others. There are probably schools of magic that are equally efficient with all aspects, although he does not know any, and they're probably less effective at any individual aspect than more specialised ones.

And you can learn several?

Yeah but it's just like learning languages, each one takes dedication and study and practice and, therefore, time.

They study dedicatedly.

The language metaphor is pretty apt; it's about as much as they advance today. And they'll have homework!

After this lesson Sadai would like to talk to Aitim again.

AItim always has time for outrageously powerful aliens!

"So I thought of a way to work around the placement limitation of portals to other worlds."