This is going to be such a strange conversation. 

Leareth heads over. Sits down. "You wished to know why I trust Bella to the extent I do?"

Nod. 

Start at the beginning. "Bella landed in Haven, not here. In addition to her Mindhealing-like subtle arts ability, she can do something called arcane magic, which is different from our kind. I first encountered rumours of her miraculous-seeming healing magic that could regrow missing limbs, which I discounted, and then I heard of her flying and otherwise being very impressive in rescuing people from a fire. I attempted to ask Vanyel about this, in one of our dreams, and he had in the meantime learned to relay Mindspeech from dreams, and so was pulling her in. At this point I had evidence of her altruism in general, but nothing very specific. I then learned from a spy that she had approximately invented the experimental study of arcane magic, after arriving in the other Arda, because in her home world, the process of doing science does not work. I was extremely impressed, and - well, it represented a vast opportunity, the resources available in other worlds, and...I hoped it might mean that I could refactor some of my - our - plans, if I could obtain her cooperation." 

This is earning him such a skeptical look. 

"She recognized, and followed, my spy, and we ended up speaking with him as an intermediary, using a magical artifact she made that increases the range of Mind-Gifts. She could also use it to directly use any of her subtle arts powers, which you can imagine are very dangerous as well as useful. I was very aware that if she were my enemy, she would have many routes to disable me. She did not do so." 

He glances at Bella. "I was concerned she would attract the attention of our gods, and made an offer to help if ever she were in lethal danger. At some point, she took me up on this, because after one very ineffectual attempt, I assume by the Star-Eyed, to send Need for her, Vkandis escalated to attacking Haven with his personal army." 

"I was also not aware until then that Vkandis had a personal army! They were from Iftel and had been keeping in form, despite millennia of peacetime, via an entire industry of blood-sports. It was very surprising! I suppose this is something your Velgarth ought to know. Anyway, she teleported me in with her spell; I shielded their House of Healing for a time, and walked a local Mindhealer through using node-boosted set-commands to incapacitate most of the gryphon cavalry. Bella did the rest, and then I decided to evacuate us - Vanyel as well, he had been injured by the enemy troops' Gate in - and took her north. Bella had a very good opportunity to sabotage my organization, and did not take it. She was also rather angry with me over my methods, on several occasions, but rather than trying to fight, she helped implement the changes she had made a case for, and was flexible on a few items where I argued the necessity. She knows the full plan and did not react with hostility, although she obviously was concerned about the risks and appalled by the cost, as any sane person would be. Before she found you, she had been intending to explore other worlds, and then revisit the question of us cooperating once she had more substantial resources of her own. Quite understandable on her part. Instead, she immediately rescued 'me' and tried to contact my organization, and has since then been trying to help you, even at significant cost and inconvenience to herself, while also doing her best to assist with your Arda's war." 

(could things. possibly. at some point. ever. start. making. sense.) 

"Anyway. I do not expect her judgement to always align with mine, but when it diverges, I think it is entirely possible that she will be right, and the difference will be that she has spent decades in paradise and I have not. I trust her to care about the world being good, for a definition of 'good' that is close enough to mine that it counts, and I trust her to be clever and actually trying. Vanyel has great respect for her, which I consider additional evidence about her character. Also, she has some idea of how to help you, and I really do not."

That definitely sounds like Leareth reasoning. 

Also, what. 

He's still kind of stuck on the concept of an entire world where scientific investigation doesn't work as a process - what would that even mean...

"Uh, a world where science is impossible means that if you try to do a scientific experiment, the world itself gets angry at you and the best case scenario is that it doesn't kill you in the process of informing you of this. There's a fairly high peak standard of living and state of knowledge, but all of that has to be derived by non-science methods, like practice and intuition and divination magic and stuff like that, never by trying slightly different things many times to see what happens."

Leareth sits bolt upright. He can only manage a sort of abstract alarm and horror about it, since Bella is still doing the calming effect, but - gods, that's one of the most appalling things he's ever heard. It's maybe slightly less appalling than the entire concept of Angband, because it's difficult for anything to rival that, but still. 

"I know," the local Leareth says, levelly. "I do not think I - we - would have survived young childhood in that world." 

"I lived, but that's why I went very native very fast in Valinor."

"So your - arcane magic, was from that world, and then you used experimentation to refine it once you were in Arda?" It's surprising hard to communicate in actual sentences with his actual mouth, but Leareth thinks it's probably some kind of suboptimal for him to only participate in the conversation via having his mind read; at the very least, he isn't sure if Bella is relaying anything to the other Leareth. 

"I wasn't relaying, no. And yeah, I had what a typical bright middle-class human nineteen year old knows and got from there to where I am over the subsequent twenty years with science and my Quendi friends."

She can relay to him if she wants, Leareth thinks, although she doesn't have to if it's too much work or anything, he can make more effort to say things out loud. If it's really another Leareth, then these are kind of his thoughts too, and if it's not real then it remains the case that none of his preferences matter. 

"Where did you get to?" he asks. (Asking also seems like a harmless action if this is a hallucination, what's he supposed to do with stories of made-up magic from a made-up other world, but he does still run that check.) 

"Relaying now," she says, and she bounces what she's reading. "Uh, the healing spell was mentioned, and I can teleport, and there's an artifact called a crystal ball that can do something like scrying but is specialized for scrying imaginary locations where information is stored like a library that takes up no space, and my boots are magic and make me not clumsy, and the earcuff was mentioned, and I had a necklace to counteract the psychological slowdown effect in Valinor but the Valar broke most of them, and I can fly..."

If it's a pretend magic system, Leareth thinks, it's not a very well thought out one. If it's a real world kind of magic then he's even more confused. "Those are all very different kinds of things. How does one kind of magic do all of them." 

"I noticed. You are correct to find it confusing. I imagine there is some theory behind why but I had not pressed Bella to share it with me." 

"There's not very much theory. I mean, the spells have parts and the parts do stuff, but it's about as much of a hodgepodge as you'd expect based on nobody being able to test anything while inventing stuff."

"All of that was invented by intuition and divination?" Looking at it from that angle, he's actually vaguely impressed. Maybe known magical techniques in Velgarth would look just as odd and random if the scientific method had never worked throughout their entire history. 

"Wizards in Materia can do approximately all the things I can do and more, though I assume they do most of them differently, except that it's supposed to be really difficult to make arcane magic do healing and I managed that."

Leareth nods. He's kind of starting to bounce off the conversation. It's interesting in an abstract way, but it's not relieving any confusion right now, if it ever was - he's ending up sort of shoving the contents in a box labeled 'probably fake'. Mostly he's tired, and tired of things not making sense, and ironically, starting to feel kind of overstimulated, but he doesn't want to tell them to go away because then Bella will stop doing the calm thing, and he's failing at being indifferent to that. 

"- with the earcuff I can do the calm thing from anywhere even if I go do other stuff, but I'll run out of subtle arts stamina eventually," she says gently. "I could put you to sleep before I go if you want, since you're tired?"