Magic Paradigms (World-building)
Magic as Science
Anyone can do magic. It's just a question of learning the proper rituals, words, gestures, mind constructs, or whatever is used to invoke it. These invocations follow fixed and given rules, so new magic can be discovered by study of what is previously known, inferring the rules behind, or by experimentation. In many ways this kind of magic is similar to the study of mathematics.
Consequences
It's very probable that this kind of magic would be able to chain-react and cause a magical revolution, similar to the industrial revolution, once the body of knowledge is large enough for synergies to become apparent.
Thus you would have a time of rapid and accelerating magical development, just like the technical development in the still ongoing industrial revolution.
However in most fantasy worlds, you want a long history of magic use, with ruins of old empires with old magic artifacts, as good as new, to discover, and long-lost myths and legends. That is, unless you try to create a theme of alienating Magicpunk, similar to the common Cyberpunk themes (as in e.g. China Miéville's Perdido Street Station).
Also, if you want to progress the story into the future, you may run into something akin Vernor Vinge's Singularity, making it hard to create a story that the players can relate to.
Infrastructure
Follows growth speed, so probably booming.
Cyclic Growth
One way of handling rapid advances is repeated interruptions that resets the development to zero, forcing it to start all over again.
Trancendence
Growth tends to evolve society into something incomprehensible, which first warps its surroundings, and then depart.
Group Mind. Outsiders. Pocket universe.
See A Fire Upn the Deep or the birth of Slaanesh in Warhammer 40k. (Part transcendence, part meltdown)
Intervention
Hubris
The gods have had enough, smackdown.
Meltdown
Accidents and War
Growth Limiters
Knowledge Horizon
Knowledge too Esoteric, takes too long to learn.
Resource Starvation
Resource Wars if metal or souls.
If magic == aura, Niven's The Magic Goes Away.
Geography Dependence
Leylines
Fonts of Magic
Repression
Forces tries to push back magic.
May cause magic to instead be pushed underground.
Superstition
Magicians are unpopular, shunned.
People tend not not persue that career because of public opinion.
X-men
Persecution
Powerful organisation actively hunts down magic-users.
Inquisition
Witch-hunters.
Monopoly
Powerful mega-guild oversees all uses of magic.
Controls who graduates as magicians.
Able to punish transgressors. Remove magic ability.
Adventures must be kept beneath the guild's horizon, or they´ll take over. Unless players == guild troubleshooters/enforcers. No world-saving without permission.
Magic Mafia?
Prey
Too powerful magic attracts hunters from beyond.
See Earthdawn's Horrors.
Magic as Unique Talent
You need som innate ability to be able to use magic.
Consequences
Magicians seen as odd, shunned, even feared.
Infrastructure
Spotty. If peple wit the talent tend to gather in specific areas, then probably mor reliable there.
Distribution of Talent
Binar y
All or nothing.
Fits class system.
Continous
Minor talents, knacks and tricks exist. Not necessarily spells.
- Firestarters
- Horse Whisperers
- The sight
- Fey touched, god touched
- The Evil eye
- Oracles
Source of Talent
Mindset
Bloodline
Patron
Faust.
Random Chance
"Radiation Accident"
Catch a falling star.
Magic as Scraps
Magic cannot be understood by people. That does not mean that you cannot use it - you don't need to understand how a cellphone works in order to operate it.
That means that packages of magic (spells, items) are used without really understanding them. New magic cannot be invented, but you can discover more scraps by looking for them. They also tend to blow up in your face if examined too closely.
Magicians are those that know how to find and use those scraps.
Consequences
Hoarding. Jelousy. Wars over source.
Infrastructure
Extremely unreliable
Boons
Magic cannot be understood by people, true, but some greater power has given us small, ready-to-use packages of it, that has been dumbed-down and deemed safe to use. It may be because it wants to empower and protect us - or it might want to corrupt and seduce us, all depending on the source.
Having a known source, you can expand the known magic by successfully petitioning it for more.
Post-Apocalypse Leftovers
People once had a more advanced civilization, where magic was understood and studied (see the discussion on magical advance above), but that civilization fell, leaving behind a treasure trove of items, scraps of knowledge, tricks and rules of thumb. These can still be used, even if the greater picture is lost.
These scraps may be jealously hoarded, guarded and fought over, or some person or organization may have started collecting them, hoping to kickstart a new period of advancement.
Road-side Leftovers
People live in the shadow of greater beings, and sometimes these beings drop crumbs that we can use.
Magic as a Mixture
Of course you don't need to have a pure view of magic. These paradigms may be mixed and matched, and there might even be different kinds of magic that follow different paradigms.
In particular, the growth limiters from the science part may also apply as extra flavor on talent-based magic.