"Reordering those a bit for ease of answering...

The world is actually loosely based on a video game - Dwarf Fortress, if you've heard of it, but I won't be surprised if you haven't, it's not very well known even here - and that's where the weird skill thing comes from. The original game doesn't have a magic system at all, but it has a mechanic where each dwarf in your fortress can (but only about 5 or 10 percent of them will), once in their life, go into what's called a strange mood and make an artifact, and at the end they get a major boost to the relevant item creation skill and also to their mood. The game is in beta; artifacts are eventually supposed to have magical properties, but in the current version they're just really fancy and indestructible, and that's what I'm going with for my world's version - the magic system I'm using makes magic items, we don't need two ways of doing that. From an in-person perspective, a standard strange mood is basically a week-long fugue state; once the person comes out of it they don't really remember what happened during that week, but the knowledge feels like they just naturally learned the skill, and the mood boost feels like justified pride at having made a really cool thing. I'm actually treating the ability to go into a strange mood as a property of natives of the world, so someone teleporting in from outside doesn't have the capacity and someone from this world teleporting out might have a strange mood while they're on their trip. If you try to do statistics to it, who it happens to and when it happens is completely random - it doesn't happen to babies but can happen to small children - but if someone has any experience with crafting, their artifact will be something that uses the general type of material that they usually craft with - metal or stone or cloth or what have you - and if they don't have crafting experience, it's always stone, wood, or bone.

The magic-related strange mood thing is different in that it's instantaneous and doesn't result in a physical item - I'm actually using 'magic form' as a concrete noun, here, and that's the created thing - but it's otherwise the same, including using up the person's capability to have a strange mood. Also, magic is an exception to the rule that if you have experience with a type of thing that it's possible to have a strange mood about, that determines what kind of thing you make - it's impossible to have a magic-related strange mood without a crystal; mages who get moods get them for the craft they have the next most experience with, or are treated as inexperienced if they don't have any mundane crafting experience.

The crystals are a naturally occurring thing - it's technically possible to make one, but there's no in-world way to see the background magical field you need to take into account, and anyway it takes hundreds or thousands of years for one to charge... I haven't determined a whole lot of detail about that, just that generally speaking the answer is 'no'. They do have to go a long time without being disturbed, so they're almost always found away from civilization, but it's not impossible that you'd find one in some ruins or even an abandoned place in the middle of a city if it's been abandoned long enough; this also explains why they're so rare and hard to find, though - you need just the right conditions for one to form in the first place, and those conditions have to be in a place that's protected from people and animals, and then whatever was protecting them has to not keep the person from finding the thing. And they're effectively single-use, too - if you touch a charged crystal and then leave it alone where it was, it'll eventually recharge but not within a humanlike lifetime; if you move it without touching it it'll retain its charge until it's touched, but moving a crystal from the situation that it charged in means it won't be able to charge there again at all unless you can put it back absolutely perfectly and not disturb anything nearby in the process.

An interesting thing about the charged crystals, while we're on the topic - once one is ready, it takes on a property related to the kind of magic it'll give, so for example the crystal that gave the original version of Lurker invisibility magic was invisible and she only knew it was there because she had a spell on her that let her see magical things, the one that gave the other version of Lurker her teleportation magic 'found' her rather than the other way around, that kind of thing.

Learning the forms uses that same touch-telepathy I was talking about - the way I'm modeling it is that each mage has a sort of metaphysical structure in their head for each form of magic that they know; it starts out very vague and undefined and unusable, but they can refine it by copying details that they see from another mage's copy via the telepathy. It's a lossy process, beyond a certain point - you can never get a better version of a form than your teacher's, unless you have more than one teacher who learned their versions of the same form from different people with different detail patterns, and copy bits of the same form from each of them, in which case you still can't get any details that one or the other doesn't have. Whether you can in theory get your form to be as good as your teacher's depends on how detailed their form is in the first place - there's a point past which the forms don't degrade unless someone just doesn't bother to learn the whole thing, but it's hard to get more detail than that and impossible to get a perfect copy above that level - the telepathy just doesn't let you see it in enough detail. The teacher's version being better does help, learning directly from someone who got their magic from a crystal helps significantly if you can put the time in to get everything you can from it, but there's always some loss in the process.

Without otherworldly magic, crystals and the mage-telepathy are the only ways of learning this magic. With otherworldly telepathy that has enough detail to it to allow communication and isn't strictly limited to something like a voice channel, if you're in telepathic contact with a mage who's using the mage-sense or meditating at all you become a mage, and if you're in telepathic contact with a mage who's actually casting a spell or meditating on a magic form, you get copies of the magic form or forms that they're using, at the same level of detail as the mage's. This is usually true even if the telepathy usually wouldn't allow for that - in particular it tends to be involuntary even if the telepathy usually only does voluntary communication, and it's especially likely to be involuntary on the mage's part. Other sorts of otherworldly magic, particularly anything like mind-reading, might be transmission vectors too, but I'd have to look at specific cases.

Learning to cast once you have a magic form is pretty intuitive - the form is a tool and a guide at the same time, once you have enough detail to use it at all you can figure out how just by looking at it - but there's a further wrinkle; there's a skill that's roughly equivalent to hand-eye coordination except purely cognitive that's involved in moving the things you see by mage-sense around to actually make the spell, and until a new mage gets good enough at that, their spells will inevitably go weird and then kill them, unless the spell is broken first. Breaking a spell that's on an object isn't hard - depending on how you cast the spell it can be as simple as picking the object up - but it's still something a new mage has to take into consideration: their spells will last a few days at most, and they have to be careful not to lose anything they've enspelled and to check them often enough, and they technically can but really shouldn't cast on people or valued animals during that period, since spells on living things can only be broken by the spellbearer's death. (Crystal-taught mages get to skip this part, it's included in the 'knowledge as if they'd been practicing for 20 years' thing. They don't automatically know that they can skip it, but if they're not familiar with mage training they probably don't know that there's a danger in the first place.)

I haven't put together a comprehensive list of forms, and I'm probably not going to - I want to leave the option open to add new forms if that's necessary for a particular character to be instantiated; it's entirely possible that the last practitioner of a particular form is living in some obscure village somewhere, or one of the animalperson species knows a form that nobody else does and the character can be a member of that species or do something to get them to teach it to them, or whatever, even without crystals involved. I can say some things about the kinds of forms that can and can't exist, but I think I need to talk about how spells themselves work first - we're missing a whole big chunk of how magic in this world works in practice, still."

"Where do the crystals come from? Are they just regular crystals that get charged up with magic, or do they just appear mysteriously, or what? After you've learnt magic from a teacher, can you then surpass them by practising? Why are spells cast on living things more permanent? Can you dispel something you cast on a living thing?"

Glam is still reading the transcript of the whole thing.

"The crystals are just regular crystals, though I might fudge the world's geology a little to make it a bit less implausible for people to randomly find them - on the other hand, cut gems and things still count, so I might not need to.

This magic system doesn't have a way of dispelling magic at all, just breaking spells, and what happens with people and animals is that the soul 'learns' the spell and reasserts it any time it would break, otherwise with how spell breaking works you almost wouldn't be able to enspell living things at all. How spell breaking works is that when you're casting a spell, the first thing you do is define what you're casting on, which can be an object as we usually think about them but can also be part of an object or more than one object - also including liquids, though they don't hold spells well - and then if-and-when the 'object' is 'broken' into multiple parts, the spell breaks and stops existing - which is how 'you can break a spell on an object by picking it up if you cast right' works, 'casting right' means including a little bit of the table under the object in the spell, so picking it up disconnects it from that part. But if it was just using that rule, an enspelled person might be able to breathe without breaking the spell, if the mage was careful enough to not include the air in their lungs as part of what they were enspelling, but eventually they'd sweat enough to break it, or have a strand of hair fall out, or whatever.

For how good of a mage someone is, there's three factors, and you get the lowest common denominator of the first two and then whatever your aptitude is for the third one.

The first is what details your magic forms have, and for that you can't surpass the sum of your teachers - you can't research it or anything, what you can see from theirs is what you can get.

The second is the hand-eye coordination thing, which isn't hard enough to learn to be a major factor in most cases - it certainly can be for someone learning directly from a crystal-taught mage; if they can't manage fiddly little details they can't cast spells with effects that require them, but for someone a few steps down the teaching chain those details will be lost anyway and a couple years' practice will be enough to let them do anything they can do.

The third one is spell design, and this is where it's possible to do new things and surpass your teacher. The forms determine what you can do, but it's kind of like legos, or programming - you can just build from the directions, but you can also take the pieces that are on offer and put them together in new ways to make new things. Not very novel new things, you're not going to get a whole new magical effect under any circumstances, but the same old magical effect in a new context could still do something interesting - like, you could take the form that lets you create fluids and repurpose it from making self-filling water jugs to filling a dirigible with helium, if you had a sample of helium and an inventor-ish turn of mind, as a fairly dramatic example."

"I'm not sure I quite understand the hand-eye coordination thing? Why is it harder to learn for someone learning directly from a crystal-taught mage?" he asks, after he's finished catching up with the reading.

"It's like... okay, detail on a scale of one to ten - a crystal-taught mage gets a ten in hand-eye coordination and a ten in the level of detail of their magic form. Someone learning from a crystal-taught mage can get their copy of the magic form up to a nine, and then to use that nine as a nine, they also have to get their coordination up to a nine. Someone who's learning from a general mage who has the usual level of detail to their form can get that same level of detail on their own form, which is like a four, and they only have to get their coordination up to a four to use it to the fullest extent possible - as they get more practice their coordination will get up to a nine or ten level anyway, but they don't get any benefit from that because they don't have a form that's detailed enough to take advantage of it."

"Is there anything making sure magic doesn't just die out, other than luck and narrative causality?"

"Most cultures have a pretty steady supply of apprentice mages to learn the forms that are common to that culture, and those forms aren't in any more danger of being lost than any other form of knowledge. It's not particularly uncommon for newly discovered forms to fail to gain traction and die out, though, especially the ones that aren't useful by themselves - for example the 'detect magic' form can be combined with the 'emit light' form to give magic-vision - the emitted light is produced very dimly in front of the spellbearer's eyes - but it's useless without a second form to actually do something in response to the presence of magic."

"Oh, so for a low enough level of detail you don't lose any more when learning? I hadn't gotten that."

"Yeah, they'd mentioned something like that."

Nod. "Yeah, at a four out of ten or below it's possible to get all the detail that's on offer. It is still possible to lose detail over time - if, say, the last mage who knows a form has an apprentice and only manages to teach the apprentice up to a three before they die, then there's no way to get back to a four from there, that kind of thing."

"But that sounds exactly like the kind of thing that can easily be patched with the occasional crystal, I think."

"If someone gets a crystal with the same form and shares the knowledge, yep. Given a long enough time span, any form of magic can come back."

"That's an interesting system. Definitely better than the strictly personal, strictly unique kind we've got going on back in my place."

"What's the power range, though? Like, what kind of things can a ten do, and a five, and a one?"

"The difference is in variety, not power, and it varies from form to form - again, I'll be tweaking this for specific stories, but not all forms have the same range of utility. On the extremes of the scale, though, someone with a one can cast a single specific spell with no modifications, and someone with a ten can do anything that conceptually comes under that form's heading, within the realm of things this kind of magic can do at all - for example someone with a perfect form for fire magic still couldn't control fire at a distance. A ten usually or possibly always gives that person a specific usage that nobody with a lesser power can do, though - for invisibility it allows limited phasing through solids, for teleportation it allows making one-way portals that people can see through, and actually one of the other authors and I were talking and for his one character who gets really crazy amounts of magic, she would find a crystal that gives her a form of magic that lets her create various forms of energy, and the capstone power on that one is that she can charge crystals.

Another thing, with this, is that not all fives are the same five, even for the same form. Different people get different subsets of their teacher's version when they get a lesser one, mostly as a function of their own and their teacher's interests."

"That's cool." Pause. "I'm out of questions."

"Me, too. I think I have a good model of how that system works in my head now, unless there's something you haven't told us. I mean, I'm guessing the actual casting of the spells is something that people sorta learn with their mage sight and stuff?"

"There's more to say about casting, actually.

The big thing is that casting a spell doesn't directly make whatever effect you're going for; when you cast a spell, you're always casting it on someone or something, maybe yourself but usually not, and then the effect comes from whoever or whatever you cast on. A spell always has trigger conditions, too: the trigger condition can be 'now', but it can also be 'in five minutes' or 'whenever the specified part of the object is touched' or 'when the spellbearer wants it to activate' or 'under the light of the full moon' or what have you. The triggers are up to the mage, which does mean that a spell can be put on someone that will activate under conditions not of their choosing; a spell like that is called a hex, and hexing people is considered very antisocial; you only really see hexes when a mage really wants to screw someone over and has decided to let their worst nature run wild, or as a particularly nasty tactic in wars.

Any mage can cast a spell using mundane triggers, which are anything that physically affects the enspelled object, thoughts and desires and emotions in the case of people and animals, and time. Generally speaking a mage who's enspelling an object to trigger based on a non-time effect will want to subject that object to that effect and see what exactly that looks like for this particular object, but for very vague triggers - 'when exposed to light' yes, 'when exposed to moonlight' no - or very familiar ones this step can be skipped. They can also incorporate simple counting and sequencing - 'when this object is touched in this spot and then touched twice in this other spot within five seconds of the first touch' is a valid trigger - but can't use any other calculations or contextual information - in particular, there's no way of telling whether a specific person is trying to activate the spell using only mundane triggers.

Magical triggers - like the magic-detection form I mentioned - and other metamagic forms can allow for more things than that, but they're comparatively rare. One that exists but might not have gained traction, for example, allows for on-the-fly modification of what an existing spell does, without having to break it and re-cast it, in limited ways - a lot of the magic forms work like programing functions, where they take certain variables and spit out a result based on them; usually, you have to fill in the specific variables for a given spell when you cast it, and they can't be changed later - so, like, the self-filling water jug that I mentioned earlier will always and forever fill itself with water - but this one form of metamagic lets you set up an option to change one of the variables later, so for example you could have a multipurpose self-filling jug with a little cup on the side, and you fill the cup with whatever liquid you want and press a button and samples the liquid like a mage would do when casting a fluid-creation spell and then fills itself with that."

"How do you choose triggers? If they can be rare? I mean, how exactly are they a limited resource?"

"I meant rare compared to other forms of magic - nothing here is a limited resource once you have it, choosing a trigger is just a matter of doing it at that point, but some things are harder to get ahold of in the first place than others. Trigger and metamagic forms have that 'the person who finds it has to get another mage's help to actually get anything useful' problem, and with learning from crystals being unknown or at best a legend in most cultures and the reluctance of most mages to teach anyone not actively sponsored by their community as trustworthy not to hex people, that's not trivial."

"What I meant was, how do you determine what triggers you can do? How do you learn to do new triggers? Or can you just set them up arbitrarily within those constraints you mentioned?"

"Ah. That's part of the knowledge you get automatically if you find a crystal, and from there it's taught in a pretty mundane way - once you know you can do those things, and the procedure for checking what an effect looks like, it's pretty straightforward to put it together from there, but the fact that you can isn't immediately obvious. There's a specialized language for talking about the mage sense - it's actually a written-and-drawn language, not a spoken one, and not every culture knows it; there might be more than one version, too, I haven't decided - that helps with describing how to do it if someone does get stuck. The time trigger is the least intuitive of the mundane ones, and emotions and desires can be tricky too, but more in the sense of figuring out how to find the right thing to incorporate into your spell than in the sense of figuring out how to do them at all."

"Looks like I'm not out of questions after all! Why is the specialized language written-and-drawn?"

"The mage-sense is very sensory and the specific sensory details matter a lot; it's hard to describe sensory details in something as abstracted as words, but it's much easier in something that's already sensory, like drawings. Like, theoretically you could take a painting and describe it in words accurately enough that someone could pick it out from a group of similar ones, but it'd be easier to draw a sketch of the most relevant defining features instead, and supplement that with words for the bits you couldn't draw. That's not exactly how the language works, there's still a translation element, but it's like... it's like how musical notation is done as drawings rather than as English words, except more complex than that; it's nonlinear, for example. You could actually think of it as more like a mapping notation than a language, if you wanted to, but instead of the mapmaker getting to pick which markings they want to use for towns and cities and roads and train tracks and make a key, there's a standard set of symbols that everyone uses, which is large enough that calling it a vocabulary is pretty appropriate."