A World Building Decision: Magic Aptitude

[(E)]

There is always a mixture of circumstances.
Partially genetic plus partially astrological has come up in fiction before.

I've used a variation on one of the methods described earlier, "magic aptitude is a combination of genetics, old bargains with powers and the alignment of the planes of existence"
The genetic and Old bargains were a justification as to why different cultural groups used magic in different ways. (Styles, rules, weaknesses).
One culture for example had no primary* magic users as a result of a powerful curse. The magic users there used trickery and chemistry to emulate magic.


*worldbuilding in that world had each culture with a primary and secondary magical style/school. For example one nation had Antimagic clergy as their primary and illegal demonology as their secondary.

[StevenH]

Originally Posted by Shuckster

Former Possession: Being possessed by a ghost or spirit, then successfully casting the entity out through shear force of will allows you to command it's power, this basically would act as the halfway point between infection based and granted by familiar as you have effectively turned the tables on a spirit that wanted to control you.

Innate but very easy to lose: everyone is born magical but due to a very common, very simple thing that renders most people non-magical shortly thereafter, next to nobody grows into a mage. This could be the simple act of having your true name spoken aloud once you are named etc.

Possession: Perhaps Magery requires you to be possessed by a ghost or spirit, where they become your "partner" who transmit their power to you in some way, for <insert in-world explanation here>.

Innate but very easy to lose: much like the language engine that the brain is born with, the magery engine will, if not exercised/trained properly soon enough, will wither away. In some cases, again like the language engine, this withering may not happen, but it's very rare.

[TGLS]

OK, some odder options:

Genetic (Dominant): Not having Magic Aptitude is caused by a recessive or group of recessive traits. Probably results in a disadvantaged minority group.

Nonesuch: Magic Aptitude locking out spellcasting doesn't exist. Traits broadly enhancing spellcasting are as elusive as talent is in reality.

[Emerald Cat]

Oceanic: Magery is dependent on the tides at the time of birth or conception of the mage.

[Phil Masters]

Originally Posted by (E)

There is always a mixture of circumstances.
Partially genetic plus partially astrological has come up in fiction before.

Well yes. "Inborn latent aptitude but must be unlocked by training" may be the single most common option in fiction, with "Can be unlocked by stress, possibly catastrophically" not unknown as a secondary possibility.

"Inborn latent aptitude, may be unlocked by training or stress, can be unlocked and transformed into something terrifying by exposure to a cosmic artefact" may possibly crop up on occasion...

[Polkageist]

Originally Posted by Emerald Cat

Oceanic: Magery is dependent on the tides at the time of birth or conception of the mage.

Atmospheric - Magery is granted by birth/conception during specific atmospheric phenomena. Alternative, magery is granted by being struck by (and surviving) lightning.

[Tymathee]

Magical biohazardous material; prolonged exposure to certain magical substances may cause long term detrimental effects on ones health but may also infuse you with magical aptitude.

[Prince Charon]

Originally Posted by Shuckster

Transhumanism: mages are only created, never born naturally, this process involves anything from bio-tech to cybernetics but the magic is surgically or artificially "installed" into the mage in some way.

Originally Posted by Tymathee

Magical biohazardous material; prolonged exposure to certain magical substances may cause long term detrimental effects on ones health but may also infuse you with magical aptitude.

These could fit together: The first mages were accidentally created by exposure to alchemical waste (one of the possibly-less-bad results of visiting a paranormal waste repository, or not knowing that there is one upstream from your village), and later alchemists refined the process so that it could be done consistently and (possibly) safely.

[DangerousThing]

There were an interesting group of fantasy books about a city, Liavek. They were short stories written by different authors.

A person's magical power was proportionate to the length of time their mother spent in labor while birthing them.

To be a mage the person had to bind his magic in an item.

In addition, during this time every year, their magic went away and they had to reinvest their power in an item. This had a few ramifications in the stories. First, the only way to provide a permanent spell (such as immortality), you needed to convince another mage to do this, because it took all their magic. Second, during this time you were vulnerable to other people. In one story, they captured the most powerful mage and put him someplace where there were no objects to invest his magic in. (He found a solution.)

[ericthered]

A different thread asked about if twins should have the same magery. Here's a fun answer: all human twins have magery and only twins have magery.