Refresher on how classes use Aether?

[MistakeNot]

Thaumaturgy uses the body's own aether to cast spells - as can be seen in the class questline with the sibling of the guildmasters who want to learn thaumaturgy, but has too low aether.
Conjury borrows aether from the surroundings - likely in addition to using the caster's own aether since that can also be used, but apparently does so at a low enough level that it is not considered harmful to the surroundings.

White magic and Black magic draws aether from the surroundings of the caster, and when used on a large enough scale can be highly damaging to the world - just like primals are a danger because they drain aether from the world around them. Used on a small scale they are no problem - the world will quickly replace the aether used.

Red mages use their own aether, but as long as they don't use too much at once it won't be harmful to them. They will recover their own aether in between as long as they don't go overboard with the usage.

The crafting classes all use external aether in the form of crystals to help their crafting. (Fire crystals for heating, wind for drying, etc. etc.)

For the rest of the DoW/DoM classes/jobs it is never explicitly explained just how they use aether - we only assume they do since some of their abilities would otherwise be physically impossible.
The DoW classes almost certainly use their own aether. The DoM classes probably do so as well.

[Vidu]

For the rest of the DoW/DoM classes/jobs it is never explicitly explained just how they use aether - we only assume they do since some of their abilities would otherwise be physically impossible.
The DoW classes almost certainly use their own aether. The DoM classes probably do so as well.

To add my knowledge/theories on how other classes are using their aether:

Maschinst:
"Next, let's talk about that contraption at yer waist. Now, I don't rightly understand it, but the boss tells me it draws on the aether in yer body an' turns it into the spark what'll feed some new devices 'e's workin' on."
Apparently they're using their own aether and then have their devices use it.

Paladin:
Seeing how they were able to use crossclass-skills from conjurer, my guess would be that they're able to utilise aether in the same way conjurers do. All their skills seem to be very "white mage"-based aswell.

Bard:
Since they dont make much use of an form of spell casting, I'd expect them to use their own aether for that one magic ability they have - the wind-magic-dot. The poison-dot is more likely real poison? And all other abilities arent magic based, seeing how they literally sing their songs to buff their friends and weaken their foes.

Scholar, Summoner, Arcanist:
I can only make very vage assumptions based on their skills: They seem to be able to draw aether from their enemies with "Energy Drain", but since thats a specific skill, I'd guess they're mainly using their own aether (they certainly do to call their pets) and pressing that into skills via mathematical-patterns. I wouldnt be terribly surprised if thats even the most effiencient way to use your own aether: By careful calculations.

Darkknight:
Seeing how the whole quest talks about "channeling the darkness inside yourself", I'd expect them to use internal aether and not draw from the outside - I'm not 100% certain that that "darkness" is also a metaphor for aether, but to me it seems like the dark knight is more self-centered in most aspects, so I dont expect them to let the land bleed dry.

Ninja:

"We draw power from the world around us─the heaven, the earth, and the hearts of man─and channel this power into physical form. I am told that this is similar to your concept of...ay-ther, was it? I must confess that Eorzean words and ways remain unfamiliar to me.
How does one channel this power, you ask? Through the use of mudra, hand gestures that call forth each of the three forms of energy of which I spoke. The first mudra I will teach you will call power from the heavens. In Doma, we call this Ten."

Sounds more like mainly external aether - even though "hearts of man" could refer to internal aether.

Dragoon:
In terms of the jobs we can pick in the game, one would need to be more specific and call this the Azure Dragoon - the Dragoon choose by the eye of Nidhogg, which is basically pure aether, and draws their power from it.
"The Eye is no ordinary relic. It harbors the power of the dragon, which it bestows upon a single chosen soul─the strongest and wisest dragoon."
Seeing hoe dragoons arent heavy-spellcasters, my guess would be that they're mostly using their own aether for all of their more magic-like things, which the azure dragoon being able to draw aether from the Eye (as long as it exists, at least).

Monk:
The whole chakra-mechanic seems to rely on internal-aether - they say that much.
But in order to open your chakras and make use of that power, you need external aether: "We stand on an ancient battleground. A great war was waged here. The spirit of the fight lingers. The aether reaches for the chakra. It aids in their opening. That is why we monks seek such lands."

Warrior:
Only guessing again, but that guess would be that their "rage"-like state is based on internal aether, rather than external, seeing how they loose their mind over it etc.

...I dont have any real argument on samurai, but seeing how that class is more actually build around swords-techniques than magic... internal?

Drawing aether from the land seems to be both dangerous for the user and damaging for the land, and seeing how most jobs dont use extremly powerful spells - exceot BLM and WHM - I'd expect them to not take the risk and just use their own body-aether for the simple, little magic "tricks" they're performing.

[LineageRazor]

Seeing hoe dragoons arent heavy-spellcasters, my guess would be that they're mostly using their own aether for all of their more magic-like things, which the azure dragoon being able to draw aether from the Eye (as long as it exists, at least).

Actually, some dragons, and Nidhogg in particular, ARE potent spellcasters. Hraesvalgr says as much when he tests us at Sohr Khai, and promises to bring his own not-insignificant spellcasting ability to bear against us to make sure we have a chance against his brother. Whether use of magic is something exclusive to the First Brood or if any interested dragon could learn if they wanted to is unclear. Dragoons, however, explicitly attune to Nidhogg, and he has no shortage of magical might.

But yeah, considering that DRGs can continue to DRG after Nidhogg and his eyes were destroyed, I'd say the power from them was a crutch, at best. Either that, or attuning with the Eye implanted a permanent and regenerating pool of dragon-aether into each Azure Dragoon, and we draw upon that even now that Niddy's gone. I, personally, like the latter explanation better, as it feels more unique.

[Genisay]

I always kind of figured that in the case of the Bard, while they use physical implements like arrows and probably traditional forms of poisoning them, that some of their fancier attacks were aether imbued, as well as weaving a degree of aether into their songs. Though since they are not outright spells, I imagine they use their own aether, and it is at a lower cost than it would be for casting classes. Empowerment more than outright casting.
Likely this is part of what sets bards apart from mere archers besides the usage of songs.

[Gemina]

...I dont have any real argument on samurai, but seeing how that class is more actually build around swords-techniques than magic... internal?

Much like NIN with Mudra, and MNK with chakra; SAM just has another name for the explosive manipulation of aether. In their case it is Sen. Iaijutsu is the process of taking the Sen/aether they've gathered and compressing it into their blade while sheathed. When the blade comes out, all that energy bursts from the edge and into their opponent(s).

All the jobs have their way of manipulating aether. 'Magic' or arcana, is just the way mages do it.

[Ramesses]

Thaumaturgy uses the body's own aether to cast spells - as can be seen in the class questline with the sibling of the guildmasters who want to learn thaumaturgy, but has too low aether.

...The DoM classes probably do so as well.

Well said, and yes, the DoM classes indeed do so. For instance, Blackmages (developed in the Fifth Astral Era) use their own bodily reserves of mana to fuel their powerful incantations but can also use their aetherial bodies as "conduits" to tap into Hydaelyn's reserves of life energy to launch their arcane spells.

Likewise, Summoners (developed by the Allagans in the Third Astral era) basically transform the essences taken from defeated primals into aetheric allies... what we call "egi".