How does magica work ?

[myahele]

In regards to ACN:

“Adepts of the art of arcanum derive their might from symbols of power born of geometric techniques hailing from across the southern seas. Held within occult grimoires, these symbols lend shape to the arcanist's aether, thereby allowing him to produce myriad powerful spells.
Using the selfsame symbols to unlock the latent power contained within gemstones, arcanists are also able to summon forth the familiar known as Carbuncle to carry out their bidding.”

In other words they use aether around them and funnel that aether into their books. That book has an "algorithm" that then shapes/programs it into a carbuncle. Additionally, gemstones contain "power" which explains why carbuncles are all named after the gemstones used in their creation. Additionally, THM/BLM use gemstones in their weapons to channel aether.

When they're finished with Carbuncle that aether is dissipated back into the land

SCH and SMN operate under the same principal due to their base as an ACN, but there are differences on the top of my head:

SCH:
Unlike Carbuncles; Faeries are permanent and are bound into their respective soul crystal. Think of them as a more advanced carbuncle especially since they'll retain all the knowledge of their previous scholar to wield them

SMN:
You summon forth the egi/essence of the primal and beat it into submission.

In either case, the amount of aether capacity/reserve you have is important. You need to have at least enough just to be able to cast spells as seen with one of the THM brothers who wanted to become a THM like the rest, but lack the aether capacity to even cast a fire spell.

Due to that, it seems like there are people that simply cant become mages

[WyrahFhurrst]

“Adepts of the art of arcanum derive their might from symbols of power born of geometric techniques hailing from across the southern seas. Held within occult grimoires, these symbols lend shape to the arcanist's aether, thereby allowing him to produce myriad powerful spells.
Using the selfsame symbols to unlock the latent power contained within gemstones, arcanists are also able to summon forth the familiar known as Carbuncle to carry out their bidding.”

So is Arcamina from Meracydia? As far as I know, it's the only continent that we know of that fits the bill.

[Belhi]

So is Arcamina from Meracydia? As far as I know, it's the only continent that we know of that fits the bill.

Originally? Its probably hard to be sure. After all Summoning is an art that works on the same principles and it originate from Allag. It could still do so, but its hard to be sure since we don't know where Nym and Allag got the knowledge originally.

[myahele]

So is Arcamina from Meracydia? As far as I know, it's the only continent that we know of that fits the bill.

Hard to say, since we know NIN, CNJ, PGL, THM, PGL and other class/ jobs are mobs in Allagan Dungeons like Fractal Continuum/ Research Facility. The fact that their called by their class names and implies that they're atleast as old as the Allagan Empire.

Since the Summoning was specifically invented by the Allagans I am more inclined to think that Aramina is what summoning eventually became due to people actively hunting and killing summoners after Allag's fall.

From what I remember Lalafells originally lived on islands within the Southern Seas and Mhachi apparently had an aliance with them against Nym