Read or Die sets the arbitrary yet consistent rule that only the most skilled paper-manipulators may use paper that gets wet.
Fullmetal Alchemist never gets into the "nuts and bolts" of how one learns alchemy or gets it to work, but we are shown though repeated example that it requires a great deal of research, practice and the use of inscribed runes or circles to make it happen. There is also the constantly repeated rule of Equivalent Exchange, that for the alchemist to create something, he or she must destroy something of equal value (in practice, this means just having the necessary raw materials at hand - the act of construction itself doesn't seem to "cost" anything, since alchemy uses geothermal energy). In fact, the author's notes at the beginning of the manga emphasize that the series was originally intended to showcase a B-movie style version of real-life alchemy, without so much emphasis on the actual science behind it. In the 2003 anime, though, it's revealed that human souls from our world are the cost being paid to perform alchemy.
Death Note: This is one of the central tropes of the series, with Light Yagami pushing each of the rules for using the eponymous Death Note to its breaking point, while his adversary L uses every clue available to determine the limits of "Kira's" powers. Some of the rules themselves are written out in an explicit, detailed manner in the first episode; others are puzzled out over time, and shown briefly in Eye Catch segments; a full list is here.
Nasu Kinoko's works have a nasty habit of setting up incredibly complex and detailed rules about The Verse... then having a character with some really rare ability break those rules. Of course, only that character alone can ever do it (and probably not more than once), otherwise it's completely consistent.
One of them: Nothing can reverse being a vampire, once you pass a certain point. Ever. Period, end of story. One character is an ex-vampire, through said convoluted spoilers. One character is almost at that certain point, and one character comes within inches of it
There is one thing that can reverse vampirism: death. The ex-vampire in question, for convoluted reasons, simply didn't stay dead.
Another example is that you can't just make stuff with magic and expect it to stay around. It'll be gone within minutes. Unless you happen to have mastered the First True Magic that is, or you're Shirou and have a Reality Marble that allows you to break that rule.
Reality marbles themselves are either a very good example of this trope or a glaring break from it, depending how you look at it. But ultimately the concept boils down to a detailed and structured set of rules for breaking a detailed and structured set of rules.
It's stated in-universe that the point of reality marbles IS breaking the rules.
Needless to say, the rules in the Nasuverse are extremely complicated to the point of Mind Screw. The fact that more than a few rules actually contradict others really doesn't help.
Mahou Sensei Negima! does well with this by only ever explaining the nature of strategies and techniques, and leaving the actual science of magic for the Lexicon Magicum Negimarium. Even still, the eponymous Negi makes it clear that he's never heard of anything like a money tree and that Love Potions aren't common and are unreliable because magic wasn't meant to be used like that (later it's made clear that Love Potions are completely illegal in Magical society). It doesn't stop Love Is in the Air moments from occuring (often hilarious).
Also, there is at least one rule Negi can break by kissing hard enough.
Well, technically, no one even knew if there was a rule concerning that, and considering that his ancestors created the Pactio system to begin with, he actually has a surprising amount of leverage.
In other words, magic still follows the laws, but one of those laws is nepotism.
It doesn't matter much because in the situation of Negi and Jack Rakan, whenever they break a seeming rule, it is brought to our attention, such as Chisame calling Rakan the man with infinite cheats, the one time he doesn't break a rule.
Code Geass has Lelouch test out via experiment the constraints of his Geass. The show mostly sticks to the established rules, but does leave vague the duration of a command.
The duration is "however long it takes to follow the command"; this has created a bit of Fan Wank as some believe that the "Live!" Geass on Suzaku means that he will eventually try to become immortal despite Word Of God saying it only triggers when Suzaku is in a potentially fatal situation and tries to give up the will to live.
For all the magic and curses flying around in Tsubasa Reservoir Chronicle and Xxx HO Li C, it is made indisputably clear that the one rule of that multi-verse is that the dead don't come back. No matter what you pay. Well, at least in the manga.
Hunter × Hunter does this with the Nen-system. Going further, while Nen itself has its own rules and limits, specific abilities can also have rules of their own set in place by their creators. Examples of such rules can be placing limitations on how and when an ability can be used. Further, due to the general rules of Nen, setting such limitations can make the actual ability far more powerful. For example, protagonist Kurapika creates powerful attacks with the limits that they can only be used against the Phantom Troupe and he will die if he misuses them. These limitations allow him to take on the most physically powerful of his enemies one-on-one without difficulty.
The rules of Immortality in Baccano! are made clear cut in episode 7 (and even earlier in the books). The rules in the book are elaborated on a bit more (primarily because at least two immortals have been spending 200 years testing the constraints), but the principles are still the same:
The only thing that can kill an immortal is to be "devoured" by another immortal.
No false names in the presence of other immortals.
Mirai Nikki has diaries that can predict the future. However, the limits of the future that they may predict does vary from character to character. Yukki, for instance, has a diary that can only predict what is going on around him, from his perspective. Yuno, being Yukki's stalker, has a dairy that updates her on things that are going to happen to Yukki. The only exceptions to the rules are if a character's DEAD END comes up, which will be a prediction of the future of the dairy holder's death.
NEEDLESS: One Needless, one Fragment. It's consistent throughout the story, with certain Fragments can imitate the effect of other Fragments to some extent, i.e. Kana'sFlamethrower is as good as the power of a Fire Needless. Of course, this rule is so totally broken by the hero and the Big Bad.
Partly explained by their fragment being the ability to learn others' fragments. Which is rather broken in itself.
Each episode of Gunbuster actually has a little "science lesson" short that explains a certain aspect of the show's universe, laying out the physics behind it.
A certain middle school class in Another must deal year after year with a curse that will potentially kill members of the class and/or their immediate loved ones. This goes on for twenty-five years, more than long enough to determine many of the rules that govern the curse. For instance, the curse only takes effect with the school's town. The one time a death appears to be an exception the actual cause of death was an injury that occurred before they even left.
The Zoids: Chaotic Century manga establishes a rule that Organoids cannot beam into any Zoid at will; Zeke needs their permission, and Shadow will kill any Zoid it beams into. The anime, on the other hand, never establishes an equivalent limitation, and as a result the series has a ton of plot holes as the Organoids behave in an inconsistent manner.
Zoids: Genesis also states that Bio-Zoid armour can only be harmed by Metal Zi weapons, and in particular are immune to beam weapons. Cue Bio-Zoids being destroyed by things varying from the aforementioned beam weapons to falling rocks.
While the individual powers and the rules regarding them vary wildly, every Devil Fruit ability in One Piece follows consistent general rules. Any exceptions, real or imagined, are typically unique and always Lampshaded.
Those who have powers are unable to swim and grow weak when submerged in water, two of the same fruit/power can not exist at the same time (though similar, overlapping powers are possible), and any attempt to eat more than one Devil Fruit is supposedly fatal. Logia-type users can become intangible by turning into their element, unless attacked with Haki or an opposing element, and Zoan-type users can transform into either full animal, full human, or a third in-between form. Tony Tony Chopper has seven forms before the time split and ten forms after, but is explained due to his medical knowledge and experimental pharmaceuticals that only he can make, and only for his own use.
The second source of superpowers in One Piece, Haki, was following this trope before it was even formally introduced. The "Color of Observation" grants Combat Clairvoyance, the "Color of Armaments" is a form of Instant Armor that can also be used to enhance attacks & weapons and can be used to bypass Devil Fruit provided defenses. "The Color of the Conquering King" is a Death Glare of Pure Awesomeness that can incapacitate the weak-willed. Perona's Hollow Hollow powers are the antithesis of this.
A third source of superpowers comes from Dials, or sea shells of shellfish that live in the sky-sea shallows of various Sky Islands. There are many styles of shell, each with at least two versions of the same effect. Example- Flame dials emit fire when the apex of the shell (that acts like a button) is pressed, but Heat dials only become hot. Sky Island warfare is the skillful use of dials, including embedding them into normal weapons, effectively giving them permanent enchantments. Usopp becomes very excited when he trades rubber bands for a huge bag of assorted dials, and uses them to upgrade the half-lame Clima Tact he made for Nami into the Perfect Clima Tact, and his own slingshot into the Kabuto.
In the Child BalladWillies Lady, Willie's mother knows his wife could not have given birth without undoing her spells, which lets them trick the knowledge of how to do it out of her.
He has to be within a certain range of the person he's mimicking. E.G., If there's no one nearby with a healing factor, he can't give himself one. If there is, he can.
He can only mimic five people's powers at any one time. If he wants more he has to "switch" one power set for another.
Each power he mimics is at approximately half the strength of the original user.
He can mimic a power pretty much instantly, but it fades very quickly if he doesn't spend a prolonged period of time (about six hours) in relatively close proximity to the person he's mimicking.
X-Men explicitly tries to be internally consistent with mutant powers in that each mutant gets one mutation, along with any Required Secondary Powers. The relatively recent "Secondary Mutations" throw that right out the window, not that it hasn't been broken often in the past.
Superman is an interesting example. When he was first published in The Golden Age of Comic Books, he was simply "leap an eighth of a mile or hurdle a 20 story building", "lift tremendous weights", "run faster than an express train" and "Nothing less than a bursting shell could penetrate his skin", or as later adapations more eloquently put it: "faster than a speeding bullet, more powerful than a locomotive, and able to leap tall buildings with a single bound". Then, The Silver Age of Comic Books started a massivePower Creep, Power Seep, with his abilities including powers as ludicrous as Super-Ventriloquism and Super-Weaving. It wasn't until later when his powers finally settled in the most accepted set nowadays: flight, invulnerability, super-strength, super-speed, super-hearing, X-ray vision, heat vision, and super-breath.
Additionally, the basic/familiar power set above had become cemented by the early Silver Age (heat vision became a permanently separate power from x-ray vision in the early 60s).
Jesse Custer, from the comic Preacher, possesses the Voice of God, which cannot be disobeyed. While this really falls more under the purview of divine power, it is not without its limitations:
First, Jesse must be physically and mentally able to speak. If he's gagged or delirious, no Voice.
Second, the subject must be able to hear Jesse. Jesse's recurring nemesis, Herr Starr, managed to escape Jesse's voice simply by covering his ears and repeating the word "no" over and over.
Finally, the subject must be able to understand the order Jesse is giving. In one instance, Herr Starr takes advantage of this by sending hitmen to kill Jesse that didn't speak English, and it's probably worth noting that wild animals don't speak any kind of human.
Fables is a bit confusing. All Myths Are True, and exist in another universe. However, Nick Slick (apparently the devil) and the Frankenstein monster seems to have always existed in the real world, and even mundane world wolves appear to have a complex language and even a religion, implying that they're far more intelligent that real-world wolves.
Partially resolved in that over the course of the series it becomes apparent that it is not our world. Jack of Fables makes it much more noticeable as it shows superpowered abstract entities do exist in the Fables universe.
The Green LanternPower Ring should be able to avoid this, as it is advertised as being capable of anything the wearer can imagine. People still complain when it does something exceptional, though, mostly because it stands out as being extremely unusual. Of course, as has been pointed out, most of the Green Lantern Corps has the imagination of a goddamn potato.
Runaways features the Staff of One, which can do practically anything (save bring someone back to life). However, its spells can only ever be used once, and attempting to cast the same spell twice would do something random. Despite this, Alex Wilder once got hold of the Staff and managed to cast the same spell repeatedly; this hinted at a loophole where you could get a similar or identical effect by using a synonym or the same word in another language. In the first Runaways/Young Avengers crossover, Nico took advantage of the Vision's on-board thesaurus and language capabilities to wreak utter havoc.
Subverted in Matt Wagner's Mage arc; in The Hero Discovered, Kevin Matchstick's mentor Mirth told him that "Magic is Green." Subsequently, Kevin's various magic feats are invariably depicted in a greenish hue. In the sequel, The Hero Defined, Wally Utt ( a different face of Mirth) said that Kevin was taught "Magic is Green" so he could visualize magic more easily. As Utt revealed, "Magic isn't any color. Magic is color!"
In My Little Pony: Friendship Is Magic (IDW)Twilight claims that even if Chrysalis drained her of her magic, the Queen still wouldn't be capable of the same kind of magic Twilight could do because Twilight gained her power through focused study. Chrysalis would have power without knowing how to use it.
The Legends Of Equestria continuity establishes some extra rules around those discussed in the My Little Pony: Friendship is Magic entry below. Among them:
There are two over-arching types of magic: light magic which is available to most ponies by default and includes the Pegasi's abilities with the weather and the unicorns' natural abilities; and dark magic, which is an independent entity that flows from the earth. Dark magic is significantly more powerful than standard light magic, but tends to corrupt everything it touches.
The story also makes a clear distinction between the concepts of magical power and magical complexity. While any unicorn, regardless of study or skill, can cast simplistic spells (such as the standard telekinesis), and can cast very powerful versions of these spells when properly motivated (i.e. being able to lift large objects or throw items with great force), skill and instruction are required to master complex magic. So only a pony that has studied extensively can work with transmutation, teleportation, time spells, thought control, etc.
Film - Animated
Disney's version of Aladdin puts rules on genie magic. They can't kill anyone, force someone to fall in love, or bring people back from the dead ("It's not a pretty picture; I don't like doing it!!!"). Genie doesn't mention it at first, but also eventually adds that they can't use their magic to serve themselves.
The Animated Series added that mixing different kinds of magic is a bad idea, because it produces unpredictable results. This is used as a reason why Genie can't just undo any magic used by villains. It's also hinted that lamp-bound genies are more powerful than free ones, presumably because the bound ones have wishes to grant.
They carry a fuel source around, and use their own body as a heat source.
Further, it also may be linked to UV radiation in the form of solar energy (when the sun stops shining altogether—not just at night—they lose their bending skills).
Richard Donner directed the first Superman movie using the word "verisimilitude" as the production motto in scripting and crafting the film. They devoted a lot of their effort to figuring out how to have things make sense within the ludicrous framework of the premise and plot. Why doesn't Superman solve all the world's problems? Jor-El's dialogue explains (piecemeal) that there is an intergalactic law not to interfere in the course of another planet's history, this rule having been put into place as the result of the early history of "the twelve known galaxies" being rife with warfare due to interference (presumably resulting in stringent vigilance for that sort of thing now, creating the potential for the intergalactic equivalent of an international incident). He is already bending the rules just being Superman in the first place. If the name "Superman" was invented by the media, why is there an S-logo on the outfit? Marlon Brando came up with this idea: The fancy traditional attire of Kryptonians included family crests in a chest insignia, and the symbol on the seal of Jor-El's clan coincidentally happens to look somewhat like an S. And so on.
One of Donner's criticisms of Richard Lester's Superman II was that it gave Superman a variety of powers that he'd never had before, including teleporting, telekinetic beams and, well, the power to pull off a cellophane "S" shield and throw it at your enemies. The audience has no trouble accepting a man who can shoot laser beams from his eyes or start hurricanes with his breath, but will immediately balk when the fictional boundaries of his abilities are overstepped.
In Transformers, one of the implied consistencies (enforced by Michael Bay) is that the robots don't do any of the "mass shifting" that has permeated all of the prior incarnations. The Robots have to fit inside their vehicle modes, no more and no less. This resulted in Optimus being a larger semi-truck model to allow for a bigger robot and the largest robot in the first movie, the huge helicopter Blackout, had a hulking robot form. They figured by keeping consistent with that, they could manage the (more difficult to accept) mass shifting of the All Spark because it was used as something special and not as a generic power of all the robots.
Back to the Future established three things about how their Time Machine works: you need to be moving at least 88 MPH, you need 1.21 gigawatts of energy and the Flux Capacitor makes Time Travel possible. The lack of the proper energy source to create 1.21 gigawatts is what drives the story of the first movie and after a visit to the future Doc Brown installed "Mr. Fusion" that eliminated the dilemma by being able to use anything to create that energy. In the third movie a lack of proper octane gasoline fuel the engine to get them up to speed is a different issue (they even made sure to specify that Mr. Fusion doesn't apply to the internal combustion engine). Some fans also noticed that the lightning strike in the second movie that shot Doc into the old west happened while the Delorean was mostly stationary, filmmakers clarified that the car rotated at 88 MPH which is seen with the fire trail after it happened.
Robert A. Heinlein's Waldo and Magic Inc. run on this trope. "Magic, Inc." uses it more or less conventionally - the magic in the story follows strict rules, which turns out to be important to the plot. "Waldo" is an in-universe example. The title character (after whom remote-control manipulation machines are named IRL) is an expert technologist and problem solver who is called in when remote power receptors are failing mysteriously. He finds that someone is fixing broken receptors /by magic/, and is told that magic can do anything - no rules. He disbelieves this and proceeds to discover the rules of magic and applies them, becoming a very successful magician as well as technologist.
The Heralds of Valdemar series is quite consistent with its depiction of magic and "mind-magic" - which starts to confuse the main characters in some of the later series, when characters from far-distant locales come in with techniques that break rules they thought were unbreakable. In particular, Gates from one location to another always require an arch or similar frame, and a single mage's own power... until an eastern mage shows up and says they've always done it in teams, and that frames are just a convenience for them.
The Adept Firesong once gave a speech declaring that most rules and limits of magic were all in the mage's head - they couldn't do something simply because the way they were taught made them think that it was impossible. And indeed, he and others did manage to do things that other mages couldn't - then a few books later he met the aforesaid Eastern mages who treat magic as a science complete with mathematical tools, and is forced to work with a group of engineers in figuring out a scientific approach to solving a magical crisis, proving that there are some real rules out there after all.
In John C. Wright's Chronicles of Chaos, there are six different, mutually exclusive paradigms of magic. Working out their relationships and interactions in a form of meta-magic is a major plot point, and the paradigms can, in fact, be charted.
The stories of Australian children's writer Paul Jennings often revolve around this trope— each has a Twist Ending which (however disturbing or disgusting) follows logically from the established rules of an item's or character's special power.
The Lord Darcy stories by Randall Garrett use self-consistent Laws of Magic to determine what can and can't be done by the characters. Appropriate, since in this alternate world magic is a science.
And "witchcraft" is used to refer to doing things that the Laws of Magic say are nonsense - like using willowbark to cure headaches when everyone knows that there's no symbolic affinity between the willow and pain. Magic as Science, and Science as Magic...
Though there is starting to be some of what we would consider more normal technological development: a top secret military research project has developed...a flashlight!
A few of the simpler rules are explicitly named in the stories. For example, there's the Law of Contagion, which allows a forensic wizard to determine whether a particular bullet was fired from a particular gun. Occasionally hints of greater detail are given; for instance, the bullet has a strong affinity for the gun, but the gun has a fairly weak affinity for the bullet... it's all explained in-story. It's strongly implied that at the higher levels Theoretical Magic is at least as complicated as Quantum Physics; one of the characters mentions that he has only a Master's degree and not a Th.D. (Thaumaturgiae Doctoris) because he couldn't handle the math.
The world of Harry Potter leaves out a lot of details about the limits and method of using its magic, and for the most part eschews explanations for a sense of wonder. Some rules are evidently made up as it goes along but the rules are never fully listed outright, which leaves wiggle room for further explanation (e.g The differences between casting "Accio Wand" and "Expelliarmus" on your opponent). Once the rules are listed, they are never contradicted, but it sometimes seems odd that certain magical abilities were never explained before. Since Harry is a teenager raised by muggles and unaccustomed to the world of magic his lack of knowledge is forgivable, while others take it for granted and have little reason to Expo Speak about it.
There are five specific things that cannot be created by magic (food, love, life, information, and money). Only the first is enumerated in the series, and only in the last book. The other four are via Word Of God, though it's implicit from the lack of those things being created by magic. They do explain that there are imitations that can be made (such making objects take on the appearance of life) and there are "cheats" that might be mistaken for breaking the rule (such as summoning already prepared food from one location to another).
One of the themes of magic Rowling has in the series is the dead can never be brought back to life, and the time after death is a mystery even to the greatest of wizards. There are several imitations of life, from ghosts, to zombies, to the echoes of people produced by a Deathly Hallow or Priori Incantum. There's also the horcruxes or the Philosopher's Stone, which prevent the person from dying in the first place, but they don't give true immortality because it's conditional on either item not getting destroyed.
But note there are other forms of magic — Perrin's wolf powers, Min's viewings, Hurin's sniffing — that don't fit within the rules and confuse channelers. Not to mention the Horn of Valere, which has less to do with magic and more with the story's cosmology. Then there's Padan Fain/Mordeth, whatever he really is, who has all sorts of bizarre abilities that aren't connected to the One Power, though mercifully he seems to be the only wielder of the "Mordeth Power".
Brandon Sanderson's magic systems are regulated to the point of being almost science. In one case, once the series was over and only about half the magic system was revealed, fans were able to correctly determine the rest of the system, based on the science of the parts that had been revealed. Sanderson owns this trope.
One-upping that, the "magic" in Margaret Weis and Tracy Hickman's Death Gate series is (pseudo)science, complete with a Technobabble—filled appendix describing how all of it works.
The Endowment magic system from The Rune Lords books is very much Magic A Is Magic A. Internally-consistent and thought out rigorously well, it was actually one of the inspirations behind Sanderson's ideas for the Mistborn books.
Bonus points, as well, for describing pretty much exactly how the magic works — i.e., instead of "he snapped his fingers and a flame appeared above them," it's "she snapped her fingers, felt the spark and heat generated by the friction, and fed it her magic until it grew into a visible flame."
Discworld magic hasn't been terribly consistent over the course of the books (Vancian Magic or Mana? It depends how far along in the series you are), but one rule Terry Pratchett has more or less stuck with is the Law of Conservation of Reality, which says that doing something by magic takes as much energy as doing it normally (although there are "cheats", such as where the energy is coming from). This stops Discworld wizards from being all-powerful Reality Warpers, but unfortunately doesn't apply to Sourcerers.
Magic in The Dresden Files has a very well-developed and consistent set of established rules. Working within these rules (and finding loopholes) is a major part of the story in most of the books. Among the most common ones:
Magic is generated by a variety of sources, primarily living things and emotions. Shown when Harry is trapped in a magic sealing field in an aquarium, and notes that there's still lots of magic inside the field because there's a lot of living things inside and that the aquarium is routinely visited by large numbers of people with strong emotions as they witness the animals inside.
Magic is affected and fueled by emotions. Powerful emotions like rage, fear, true happiness, etc. can make spells more powerful than usual or even fuel spells by themselves, but any sort of delicate magic, such as complicated rituals, requires total calm lest they backfire and blow your head off.
Magic is bound by the laws of physics. Harry's wind spells still need air to move, fire spells suck the oxygen from an area (and the energy can be drawn from ambient heat), and force spells still operate based on Newtonian physics. Creatures with Super Strength are helpless if airborne, for example, as they are at the mercy of physics without anything to push against.
Magic is defined by human thought. This is why wizards use a variety of dead languages to cast spells. The words simply help the wizard shape exactly what they want the spell to do in their minds. Amateurs need rituals, lengthy chants, and meditation to do even simple spells while more experienced wizards can do the same with a single word. You use a dead language because the magic becomes linked with the word in your mind. Use the word "fire" for fire spells and you'll be burning your house down within a week. Don't use words, on the other hand, and the magic comes out raw; the one time we've seen this in the books, the person trying it turned into a human TASER while having a seizure.
The exception to this are the very powerful or experienced wizards. Senior Council members can potentially cast spells without using words, like Ebanezar McCoy, and the Archive can fling literally dozens of spells off without speaking. Of course, the Archive is the living archive of all recorded knowledge, and knowledge is power. Note that "Ivy" is not a magic practitioner in the conventional sense; normal people can use magic to a limited extent, but it's like a blind person trying to paint. Ivy has the same amount of magical talent as most people. Her immense magical ability is nothing but skill and knowledge, like a blind person painting ten Mona Lisas with their feet.
Religious faith has been described as something "like" magic, but not quite. Magic is compared to feeling like electricity, while faith more like a deep ocean. The main use of faith seen is that it can harm certain supernatural beings (most prominently Vampires) and can negate supernatural powers(Micheal's duel with Nicodemus in Death Masks).
Using magic physically tires out the spellcaster. Throwing around magic wears one out like doing any other act of physical exertion; dropping lots of energy can make one black out if used too quickly or too hard.
Magic can be targeted using connections between objects, i.e. a spell can be targeted against a person by using a sample of hair, skin, or blood, or an object can be tracked by using a small piece of it. This is used throughout the series to do everything from tracking down lost items to eavesdropping on conversations to launching heart-exploding spells at targets. Harry takes this to a rather impressive extent by taking tiny samples from every building, tree, and street in Chicago and making a precise scale-model replica of the city that allows him to work tracking and eavesdropping spells across the entire city. However, this magic can only used so long as the two objects have a direct connection- hair clippings, for example, could not be used to find someone who'd shaved his head at some point after the clippings were taken because the clippings no longer matched up with any of the hairs on his head.
Mortals and certain other entities have will and choice, which are actual forces in the setting. It is what separates humans, the various types of vampires, and other denizens of the mortal world from denizens of the Nevernever. Humans and other creatures with willpower can create circles of willpower that trap, cut off, and contain magic and can hedge out entities without willpower.
In the latest novel Cold Days, mortal willpower becomes an even more crucial force, making the entire difference in several life or death battles.
Physical contact between magically-sensitive mortals generates a detectable field. Making eye contact with a person with strong magical ability triggers a "soulgaze" that shows both participants the true nature of the other. Anyone with sufficient talent at magic can initiate the "Sight" which allows them to see reality as it "truly" is - letting them see magical auras and determine the true nature of creatures and locations - with the downside that the person who uses the Sight will retain that knowledge with perfect clarity (so if you look upon a victim of a psychic mauling or an Eldritch Abomination, time will not dull the edges of the memory).
Another very important aspect of the magic is that in order to use magic you have to believe that what you are doing is right, which is why killing someone with magic is such a terrible thing- you have to believe that you have the right to kill them. This creates a psychological effect on anyone who uses magic to kill or tamper with the free will of another human, which inevitably leads to Jumping Off the Slippery Slope and becoming a raving psychopath. This is the basis for most of the Laws of Magic enforced by the White Council.
Magic in Rivers Of London, at least the type practised by human wizards, appears to be exceptionally rules based and its apparent violation of the laws of thermodynamics greatly worries apprentice Peter Grant.
But Beverley Brook, a minor river goddess, seems to do magic in an instinctive fashion.
Magic in general seems to work off of Newtonian physics. Throwing a small pebble at a certain speed requires as much energy as if you did it by hand. Then you have to consider how far away the target you're enchanting is and even the very wording you're using in the ancient language, all of which can determine how much energy you could spend on a task. This law can get abstract when you're dealing with metaphysical concepts like turning invisible, healing wounds ranging from cuts and bruises to broken bones and birth defects, and amalgamating enough particles of pure gold to be the size of your fist, to the point that experimenting with magic is extremely dangerous because you don't know exactly how much energy it will require, and it WILL kill you if you try to use more energy than you have..
Except when it doesn't, eg, dragon riders can borrow their dragon's hit points (and dragons have plenty to spare, since they are quite large). As of Eldest, Eragon learned he could also use the life energy of plants and animals around him. As of Brisingr mages can also use "Eldunari," which allow you to borrow a dead dragon's hit points.
This is still within the rules as where the life energy has to be from is never specified, just that it is used.
Angela knows a spell which uses dragon bones to predict the future, although she herself admits that interpreting them is tricky. A group of elves at some point created a spell which could outright see the future, no interpretation necessary.... and it killed them when they tried using it. Trying to raise the dead will also cause instant death. In the last book, Eragon considers trying to bring Brom back. However, what he seems to be suggesting sounds more scientific (use magic to repair the body, repair the brain, use telepathy to give the brain its memories and personality, then jumpstart) than summoning Brom's soul from beyond the void, which is specifically what he was warned against. In any case, he decides against doing it.
The Rules of Magic (or how it works) are seldom explained in J. R. R. Tolkien's Lord of the Rings - the lore and magical words are well outside the ken of the hobbits. Even people who ought to know (such as Elrond) express some ambivalence on the potential effects of, say, destroying the Ring. Still, this doesn't stop fans from getting into debates about whether the Nazgul wore their Rings or if Sauron had them on his person.
It also seems that what is considered magic by, say, Hobbits, isn't always thought of as such by, say, Elves, which makes explanations difficult and/or unnecessary.
"'Are these magic cloaks ?' asked Pippin, looking at them with wonder.
'I do not know what you mean by that,' answered the leader of the Elves. 'They are fair garments, and the web is good, for it was made in this land. They are elvish robes certainly, if that is what you mean." ("Farewell to Lórien", The Fellowship of the Ring.)
This is because, as Galadriel points out, the word for "magic" used by the hobbits covers what to the elves are two distinct concepts, both elvish "Art" and "sorcery" which is the term for the works of Sauron and the Ringwraiths. Of course, even in Sindarin the term for "sorcery" is just the prefix for "dark" or "black" (mor-) thrown on the word for art, lore, or knowledge (gul, thus sorcery or "the black arts," is morgul as in Minas Morgul and the morgul blade.)
Additionally, as is made more clear in the Silmarillion, elves simply don't think of what they can do as "magical." It's just a natural ability to them, like carpentry is to a human being — as far as the elves are concerned, they're just better at making things that us weakling humans. Basically, an elven sailor could get so good at sailing that he could make his ship fly. Likewise, the "wizards" (istari) like Gandalf aren't stock fantasy wizards so much as actually a group of minor gods (the same kind of being as Sauron and the Balrogs, actually).
It's also worth mentioning that in one of his essays, Tolkien specifically mentioned that in a true "fairy story", magic should never be explicitly explained.
A point is made in the Silmarillion that many great works that might be considered magical can only be accomplished once. The great trees: Telperion and Laurelin, created by Yavanna could only be created once; the Silmarils created by Feanor could only be created once. One may presume the One Ring created by Sauron could also only have been created once and it would make sense that reason for this is as given that he put his own power into the ring thus diminishing it in himself. In this respect the act of using one's 'magic' to create a great artifact appears to forever diminish the creator of the artifact.
A rather interesting case in Shadows of the Apt- humans all possess the Art, giving them powers and abilities based on the particular insect-archetype. This is all inherited- if you have Beetle parents, you're a Beetle yourself and you get Beetle Art. There's also Aptitude- either you're Apt, and can use- and learn to create- technology, or you're Inapt and can't even open a door with a spring-latch. However, the Inapt can learn magic- another interesting part being that if you see Art, you know it's Art not magic.
Jim Butcher's Codex Alera is a close parallel to Avatar: The Last Airbender. Furycraft is basically bending spelled sideways... though the rules in detail are different, and while strong mastery of more than a single element is rare, it is not at all unique. All the High Lords can do it. A significant feature is that it is an important issue in the series that furycraft can be treated scientifically, and while the limits are stated well, a sneaky enough furycrafter can come up with surprising new twists, yet still within the rules.
While Merlin in T.H. White's The Once and Future King can display spectacular power (such as causing a tree to instantly grow and bringing about a snowstorm in the middle of summer) he has some clear limits on what he can do. The only two powers to which he has continual access are Insight (being able to see events going on at the present) and Foresight (being able to see future events; part of the latter is due to Merlin's being born circa the late 20th Century and living backward through time). It is stated that Merlin could not use magic to imitate the Great Arts, such as Falconry or Sculpture, as it "wouldn't be fair". Also, Merlin was "given" his magical powers for the specific purpose of helping Arthur prepare for the kingship, which is why cannot transmute Kay into an animal like he does Arthur.
The Belgariad has "the Will and the Word" - you gather your Will and focus it with a Word. This uses the same ammount of energy as doing it any other way, but means you can pull in energy from your surroundings and apply it with more flexibility. The exact nature of the word isn't important (though Belgarath chides Garion several times for choosing insufficiently impressive words,) but there does need to be a word.
Most importantly, the one thing magic cannot do is "unmake" anything. It can kill and destroy, for that just changes live people to dead people or whole objects to broken ones, but it cannot erase anything from existence. Doing so causes the universe to take massive offense, protect the targeted object, and annihilate the sorcerer. (As a corollary, this means that there is one object any sorcerer can freely unmake - themselves. Several characters have either attempted or committed suicide this way.)
It is theorized that many mages who never had ay practical training accidentally killed themselves by trying to annihilate objects. When the group meets a two-hundred year old scholar whose work was ignored because all of his apprentices mysteriously vanished, they find that he is a really nice guy and the worst thing he ever did was teleport an assailant out to sea.
It also includes the fact that Newton's Laws of Motion still apply, and not pulling energy from elsewhere will drain you quickly. The main character, Garion, tries to lift a large rock when he first learns of his power. He succeeds, but then becomes very dizzy, falls asleep with his head on his arms, and only upon awakening realizes he didn't lie down. Instead, he is up to his armpits in soft soil.
In The Name of the Wind, magic is surprisingly mundane and consistent. The most common type, sympathy, follows (really follows) the law of conservation of energy. For example, if you bound two coins, lifting one would lift both, but it would weigh like both, not accounting for the loss of energy (the more similar, the less energy lost). One can use an outside energy source, though (like, say, using a fire's power to move an iron wheel). Sygaldry is sympathy, but based on written runes, and Knacks are individual and very mundane skills (always getting sevens when rolling dice, growing very large fruits). Lastly, Naming is barely explained, but it's rare, far more powerful than sympathy, and described as "fairy tale magic". There is also the even rarer Fae magic, grammarie and glamourie, the art of making things BE, versus making things SEEM.
The same University that teaches these arts also teaches medicine, informatics, rhetoric, and linguistics, which aren't exactly magic.
Subverted in the Collegia Magica trilogy by Carol Berg, in that this is certainly how it is taught...whether the true nature of magic follows this trope or not is a different matter.
Superpowers in The Grimnoir Chronicles books fall on a grid that is one part The Quade Diagram and one part ROYGBIV. All supers start out with a single power which either comes from one part of the grid or the overlapping of two or more parts. In turn, the kanjibrands are two-dimensional sympathetic representations of whichever part(s) of the grid the user wishes to draw power from.
Averted in the Shannara series, where it is made very clear over and over that magic is highly unstable and unpredictable, prone to shifting over time from one form to another. Even well known and fairly well understood magics can occasionally have unforseen effects.
In the Time Scout series, there are a few rules to time travel that aren't broken.
No paradox. Don't bother trying.
If you exist twice in the same time, you'll die. It's called shadowing yourself. You can't cross your own shadow and live.
The Alex Verus series has a fairly definite set of rules for the powers the mages can use. The author even has a series of articles on his website called the Encyclopaedia Arcana talking about it.
Zenna Henderson tended to do this with the psychic powers of The People.
David Friedman's Salamander opens with a college lecture on the laws of magic.
Live Action TV
Despite the fact that in part one of The 10th Kingdom, Wendell's transformation into a dog and of the dog into him is shown through a now-somewhat-dated but still effective slow-morph, his later restoration at the end of the series occurs in only a few split seconds while he and the Dog Prince whirl around in each others' arms and then fly apart with a burst of magical sparkles. The only explanation for this sudden change in the speed of transformation is an attempt to show off the special effects, most likely as a minor example of the Rule Of Cool. (More dramatic, after all!).
Mahou Sentai Magiranger had a well mapped magical system; there were multiple tiers with 10 words each, but said words could be combined in any which way a character wanted to do different things. The fact that the main heroes were breaking the tier system by the end of the season gave a feeling of "they're more powerful than any magicians in history" instead of ruining suspension of disbelief, because the usage still remaining consistent within the tier breaking.
On the other hand, the US version, Power Rangers Mystic Force, fell prey to the consistency ditching pretty quickly. Whereas the magic syllables were made up words that signified general intent in Japan, they became Harry Potter-copy Latin/Welsh translations in US, making it less of a detailed system and more "use whatever works whether it contradicts previous usage or not".
The later series Samurai Sentai Shinkenger has magic called Modikara invoked by writing the appropriate kanji character in the air using their magical paintbrush/cellphone transformation device. Writing the kanji for "rock" (石) will cause a rock to materialize, and writing the kanji for "horse" (馬) will also cause a horse to appear. The kanji also has to be written properly, a fact Chiaki learns early on when his terrible penmanship prevents him from using Modikara because he never learned how to write the kanji for "grass" (草) with the proper stroke order. Genta, who does not have the paintbrush/cellphone, instead uses a text-messaging interface on his cellphone transformation device.
Power Rangers Samurai has kept this system, but uses different kanji in some situations. To their credit, this series hasn't fallen into the "just make stuff up" trap that Mystic Force did; replacement characters are still actual kanji and still relevant to what the Rangers want to do.
Any number of superstitions regarding behavior of mythical creatures that "haunt" people. For example, salt keeps evil spirits at bay. Many of those rules are actually very consistent, if you know from what leaps of logic they spring. (Salt keeps food preserved, rot is caused by unclean spirits, ghosts are unclean spirits, therefore salt = no ghosts.)
On the other hand, similar things from different cultures and times can sometimes result in a lot of mythological mashups. The result being many different rules that were consistent becoming inconsistent because they're being applied to each other.
The Expanded Psionics Handbook in Dungeons & Dragons has no less than two sets of alternative rules for running a "Psionics are just different" game - either making them 100% independent of magic (so spell resistance, Dispel Magic and so forth don't work on them), or making them about 45% independent (so you need to make a caster level check to use Dispel Magic on a psionic effect, and your power resistance is 10 lower than your spell resistance). The default (and balanced) setting is the are interchangeable for such purposes and at least 1 setting has psionics as explicitly a separate type of magic.
They also have two different flavours of magic, depending on what its source is - Arcane or Divine. Arcane magic comes from wizards memorizing spells and using hand gestures to cast them (and so can be screwed up by wearing armour that restricts your movement and gets in the way), whereas Divine magic comes from the Gods and has no such restriction. Also, for the most part, healing spells are limited to divine only (except for Bards, who do things their own way).
Which gets rather head-scratchy in some of the official worlds such as Dragonlance, where Arcane magic is separate from Divine magic, and yet still comes from gods, and you get it by worshiping them.
The arcane/divine split is just a convenient Hand Wave to keep wizards in particular from (a) wearing armor and (b) using healing magic (both of which Bards, also arcane casters, do just fine), both purely for purposes of game balance. It's probably best not to try to read much more into it than that.
They designed clear rules for exceptions to the armor rule, with coresponding limitations. It is possible to get a wizard to use magic in armor, but with a drastic restriction in which spells they can then use as they have to then specialize in just one type of magic and only in specific spells. Look up the Battle Wizard build, which allows for casting in medium armor without penalties, but with a drastic reduction in versatility and number of spells they can both learn and use.
The fluff regarding the difference between Divine and Arcane magic varies by setting, but one very common tendency is that divine magic requires one to act as one's faith would have it (or at least to be able to convince oneself of that), whereas arcane magic have no such compunctions - that highly religious, saintly wizard can one day wake up and decide to become evil for his own sake rather than for any god, and it would not impact his ability to cast magic in the slightest.
In earlier editions, psionics did not interact with magic. The system was a completely bolted-on addition which barely fit the rest of the game and could be horribly broken when a wizard or paladin, no matter how powerful, was just as vulnerable to a 2nd level psionic character as a peasant. Additionally, the rules for psychic powers required ability score checks against variables and had their own, separate, entirely different mechanic for psychic combat. Defenses against psionics for non-psionicists barely existed. Gaming groups often would rather forget psionicists existed than deal with the headaches you get from averting this trope.
There are three set rules for magic in Exalted: "No time travel", "Once Exalted, you cannot Un-Exalt."*
Elaborating: Un-Exalting results in death, no exceptions.
and "No resurrections." Of course, this being Exalted, those rules exist mostly for Solar Circle Sorcerers to kick them in the nuts and steal their lunch money, but you will never see official Charms or Spells from White Wolf that allow you to break those rules. Bend, maybe. Break, no.
It should be noted that the 'no unexalting' rule has found some limited exceptions. It assumes that on a mystical level, the Exalt remains fundamentally human. Green Sun Princes who 'ascend' to full Primordial status with Heresy charms find their Exaltation flitting off to find a new host (not that they need it at that point). Likewise, Exalts who chose to take up a job offer to divinity extended via Greater Sidereal Astrology find their Exaltation moving on once they become Gods. It should be noted that in both of these cases, the exception is allowed because the action of releasing the Exaltation is a choice, and cannot be driven by any supernatural or unnatural compulsion at all else the powers fail to work. The more precise law would have to be "Exaltation cannot be taken away from Exalts, ever".
Of course, viewed through another lens the example of becoming a God or becoming a Primordial results in the end of mortality... which looks like death to the Exaltation. In the First Age, the Solar Queen K'tula twisted herself into a fundamentally inhuman cephalopod horror to the point that many of her Solar charms ceased to function properly (because she was no longer remotely human), but her Exaltation lingered because she was still unmistakably alive and mortal (in the sense that her lifespan wasn't infinite).
Likewise, there are hardwired rules on just what certain Exalts can do that other Exalts can't. Sorcery's available to all Exalts, but Dragon-Blooded only have the ability to power first circle (Terrestrial) spells and only Solars can power third circle (Solar) spells. The only way around this is with extremely powerful artifacts, such as the one that allows the Scarlet Empress to use second circle sorcery. Martial arts are likewise available, with a slightly different theme of everyone being able to attain a level above their station with huge enough effort. Mortals can enlighten their essence and use Terrestrial Martial arts, Terrestrials can refine themselves to use Celestial martial arts, and Solars/Abyssals can use Sidereal martial arts if they somehow manage to find a teacher, which is probably harder than the former two examples. The exception here are Lunars who cannot learn the highest tier of martial arts at all, only their own Celestial tier. Necromancy can only be learned at the highest levels by the Abyssals, and everyone else is capped at once less than what they have learned in Sorcery, meaning Dragon-Bloods can only cast necromancy if they forsake the ability to use sorcery. Technically everyone can learn all of these charms and spells though, even though their exaltations are too weak for them to put them to use
Dragonblooded can actually learn Celestial Martial Arts, but doing so is considerably more difficult for them - considering that such arts are a tier above their own native charms in terms of power, however, it's well worth the effort.
There is an exception to the "No Resurrection" rule, and it's a long story why and how it can be achieved. When the Primordials surrendered to the Exalted hosts, they forego their ability to rewind time and undo death in Creation. Said Primordials are then imprisoned/become Hell. In Hell, they can do whatever they want, as long as the aforementioned term is not violated. In practice, now-Yozi primordials can undo casuality of something that happened within the last 5 days in Hell. This means that if your significant other died in Hell, you can surrender his or her thread of Fate to the Yozis, and if the Yozis see something to be gained from undoing the demise of the deceased, then a resurrection is in order. Considering who the Yozis are, it's an almost-certainty that the person will no longer be the same as who he or she was...
The "No Time Travel" rule was repeatedly broken during the Primordial War(s), and there is nothing stopping you from playing a game set during that turbulent period. This was a time when Reality itself was the casualty of the war, so don't expect that rules taken for granted today existed in any form back then.
The magic in Shadowrun has similar rules to Exalted: no resurrections, no time travel, and no teleportation. Furthermore, if you do not Awaken naturally, there is (practically) no chance that you ever will. That said, there are still several different flavors of magic-user.
Adepts are limited to one type of magic; this can be casting spells (sorcerers), summoning spirits (conjurers), or enhancing the capabilities of their own bodies ("Phys-Ads").
Magicians can both cast spells and summon spirits. The exact style and trappings of each magician's talents varies from one practitioner to the next, but the two most common catchall terms are hermetic mages and shamans. It should be noted that, despite the names, there's no arcane/divine magic split; anyone capable of sorcery can learn and use any spell.
The indie superpowered-sleuth system Mutant City Blues elevates this to new heights. Sure, there are mutants in the setting, and they can fly, shoot assorted kinds of energy bolts, read minds and even steal each other's powers. All these powers, however, are meticulously catalogued in the so-called Quade Diagram which provides solid insight about what powers can concievably coexist in a person. Some, like supernatural analytical abilities and remote control of electronic devices, are very *close* so that the person possessing one can be routinely assumed to posess another. Others, say, the ability to fly and become invisible, are so far apart in the chart that it is impossible for one man to have both (without breaking the setting and/or having Infinite Experience Points). This diagram, along with more conventional investigative methods, makes the task of solving "Heightened" crimes more of a usual analytical exercise and almost none of the "whoever got more control of The Force" challenge common for less defined supernatural settings.
GURPS Thaumatology is a sourcebook dedicated entirely to making up bizarre, yet internally consistent, magic systems. GURPS also has a completely separate system for "psionics," which can be the same exact force as magic, but which are administered in the form of traits specific to a given character, rather than general rules that all magic users have to follow. That's where you go for Wrong Context Magic.
Warhammer 40000 has a very simple magic (all right, 'psychic powers') system allowing various psykers to do different things (mostly attacks or buffs), though they all have a chance of suffering the consequences.
Warhammer Fantasy has a more detailed system that has most people drawing on a collective library of spells, though Lizardmen, Chaos, Undead, Orcs and Goblins, High Elves, and Dark Elves all have access to an extra group of spells.
In Ars Magica, wizards can do virtually anything, but every spell they case must be formed by combining, basically, constructing a Latin sentence consisting of one of five "techniques" (the verbs, all with the subject "I") and one of ten "forms" (the direct objects). For example, throwing bolts of flame would be "Creo Ignem" ("I create fire"), while making someone forget something would be a "Perdo Mentem" spell ("I destroy the mind"). Every wizard has varying levels of ability with each form and technique which determine how powerful of an effect they can generate (someone with a high score in Creo is good at making things in general; someone with a high score in Mentem is good at working with people's minds in general; someone with high scores in both Creo and Mentem would be extremely good at putting thoughts in other people's heads). Each edition of the game also has a few hard-and-fast rules beyond the verb/object format, such as it being impossible to raise the dead or travel back in time, although whether those things are literally impossible or simply unknown or forbidden to members of the Order of Hermes (the organization player character magi are assumed to belong to) is generally unclear (by design).
Mage The Ascension (which draws from Ars Magica to some extent) and Mage The Awakening have spheres that work like the "mind" side, and can also be combined (e.g. Correspondence + Mind to mess with someone's head from a distance). Changeling: The Dreaming uses a two-factor system (along the lines of "the mind of a human" or "the mind of another fae"), as does Geist: The Sin-Eaters (where a Key determines general dominion and power source and a Manifestation determines what you can do with it).
World Tree RPG uses a noun/verb system (7 and 12 of each), but lets several of each be combined in one spell. Eg. a life-extension spell involves "Sustain/Body+Mind+Spirit". And that's the standard "pattern magic", one of several systems the main races know, each with known rules. The trope is played straight in that the rules exist, but subverted in that ultimately the gods control magic and don't do it predictably.
Magic: The Gathering bases everything around its Golden Rule: when a card contradicts the rules, the card takes precedence. This makes sense, since the players are Planeswalkers, beings explicitly stated to be able to violate a particular plane's magical laws by nature. So while the basic rules of the game and its universe are in a constant flux, the reasoning behind it is consistent.
In Bell Book And Candle, Gillian explains that the effects of spells have to look like coincidences: "I can't bring Niagara Falls down to Grand Central Station, or turn this house into the Taj Mahal. It doesn't work that way."
The magicka in The Elder Scrolls is an excellent example of this trope. It's never explained in full detail; but it's established as something anyone can practice it in his spare time, but also subject to substantial research by the Dunmer Temple, the Imperial Cult, and the Mages Guild. There are also some very clear rules: to enchant an item, you must know the spell you'll burn in the item, you need a soul gem with an animal soul inside (you can't trap human, bestial or elven souls), and clothes and accessories can hold much more magic than weapons.
While enchanting is consistent within each game, the exact mechanics tends to vary wildly throughout the series as a whole.
Oblivion showed us that, using Necromancy, it was possible to create a corrupted form of soul gems that are made for capturing Human, Bestial, or Elven souls. And they're more powerful than most animal souls, to boot. They're not available in Morrowind, though, because necromancy is banned in the Morrowind province by the Dunmer Temple.
In Morrowind you could trap the soul of a demigod and it is very powerfull indeed. Trying to mess with how magic works also tends to end badly, especialy with Necromancy and Conjuration. Two Oblivion quests also center around the consequences of using magic to travel into your own mind. In one of these quests a divine artifact gets involved and the dreamworld imposes itself on reality inside of the poor wizards tower.
Except with the Khajiit, which has resulted in a tangle of lore to reconcile those inconsistencies that puts most fandoms to shame.
There are many esoteric rules that are referenced throughout the series but don't appear in actual gameplay. For example, some magic requires "rituals" to perform, such as necromancy or permenant conjuration, which explains why the player can't use them in-game. "Daedric magic" is mentioned as a quick way for eager mages to get their hands on volatile power, though this isn't really elaborated upon.
It's hinted at with the Sigil Stones in Oblivion: at higher levels, they're more powerful than Soul Gems, but they can only bestow one spell effect on a weapon or piece of armor. In short, it's a quick-and-dirty way to get a super-enchantment on anything you want, that doesn't even require an Altar.
Finally, it appears some, most, or maybe even all rules of magic can be stretched, if not necessarily broken; Ancotar states that permanent invisibilty would "violate the Conservation of Perception," but has created a spell that can keep a whole village invisible for at least a year.
And in Tales Of The Abyss, this trope plays a significant and often heartbreaking part in the plot - even to the point of explaining exactly why the Big Bad's plan requires destroying the world. It also forms much of the character development of reformed Mad Scientist Jade Curtiss, who simply cannot do some things like saving Luke from vanishing due to fonon separation, no matter how skilled he may be at fonic artes.
Kingdom Hearts plays with this, where certain things will be described and appear consistent... until something comes along that 'breaks the rules'. The authorities on that particular subject will subsequently be as confused as the player, demonstrating the Aesop of “Attempting to apply strict rules to natural phenomena is foolish, as the world is chaotic and wonderful”.
Magicka revolves around this. Players have eight basic elements with which to cast spells. Each element has given properties and can be casted directly forward like a projectile, in an area around the caster, or on the caster. There are also opposing elements that will cancel each other out if used while conjuring a spell, or worse. It is very possible to kill yourself with ease or heal the enemy by accident.
Though the FEAR games do not generally provide hand-and-fast rules on how the psychic abilities of Alma work, the abilities of the Point Man and Paxton Fettel are fairly consistent. For example, the Point Man's slo-mo/reflex abilities can only be used for short periods, while Fettel's possession powers will kill anyone he possesses shortly after taking over their bodies. Including Michael Beckett.
Dragon Age has, among other restrictions, "The Rules" which apply to magic: it's impossible to raise someone from the dead, it's impossible to use magic to travel any faster than "putting one foot in front of the other" (anyone who appears to be teleporting is actually just using an illusion to make them appear to be in one location while they hide and run somewhere else), and entering the Fade physically, while it's technically possible, requires an EXTREME amount of resources (lots of lyrium and Human Sacrifice) and is a VERY bad idea likely to result in divine retribution. In addition, magic requires that mages expend mana (and/or lyrium) or blood. Exactly how other things work (magical healing and the darkspawn taint in particular) sometimes varies.
The webcomicOrder of the Stick does this with D&D rules (mostly). For an example, there's a strip where Durkon uses Weather Control to attack a group of treants warded against electrical attacks... by generating a thunderclap so loud that it breaks the treants in half. When an angel tells Thor (Durkon's patron god who enabled the spell) that that's not how the spell works (Weather Control doesn't cause sonic damage), Thor tells him to be quiet because it was awesome.
Tales of the Questor has "magic" that is, essentially, Sufficiently Advanced Science—- Magic is actually a natural ability to manipulate an exotic form of energy, can be used via technological means, and generally follows the known laws of physics (Conservation of mass and energy, for example, still apply).
A Magical Roommate is fairly flexible, but has some strict rules with its magic system. When it appeared that one of these rules had been broken, Aylia imediatly rushed to figure out how... only to discover Loophole Abuse the cause.
In Homestuck the video game sBurb (or sGrub), around which the plot is based, has a series of strict, consistent rules. Its Time Travel rules are also internally consistent.
With that said, the few "magical" concepts that pop up (usually with Rose Lalonde) tend to be loosely defined and fairly inconsistent, because real magic (ie. not based on an explicit Reality Warper's powers or on sBurb itself) is fake as all shit.
Strong Bad, in his shapeshifter e-mail, thinks of the qualms that would accompany shapeshifting. For instance, he can turn into any species of balloon animal, legal tender, has the sound 'dwayne' accompany every transformation, and turning into almost anybody in the world (that is, one-half of the intended person, hence the "almost").
In Arcana Magi, Mana is a source of energy akin to electrical energy, with kinetic and potential types. Mana energizes magical items and can be drawn from nature by people with magical powers to cast spells, but cannot be drawn from other people or creatures due to willpower and instinctual resistance. Mana is 100% pure when the object its drawn from is natural, like copper and wood, and slowly but surely the natural object will lose all its Mana when changed into something else, like when copper and electricity is used in a computer. Though in Arcana Magi Zero, different types of magical groups have different ways of drawing mana and casting spells. For instance, Alysia Perez and Megumi Miyazaki are Circular Magi, so all their magical powers come from Magic Circles.
Explicitly averted in Tales of MU, where the laws of magic will change if they detect someone trying to figure them out. In-universe, science is a heavily discredited pseudo-, uh, science, much like people who believe in All Natural Snake Oil in the real world. How, then, does the heavy use of Magitek work, in-universe? Well, that's a good question...
There's a difference between craftsmanship and science. You can make a gun without knowing ballistics.
That's as may be, but you still can't invent something without understanding the principles that make it work.
Pointing out this inconsistency to the author is an excellent way to make her not pay attention to you anymore, however.
While any sort of magic (from Hermetic rituals to Native American Ghost Magic to Voodoo to Chinese Necromancy to Holy Miracles to Australian Dreamwalking) is possible in the Global Guardians PBEM Universe, each particular type of magic is internally consistent for that type. You don't find Hermetic mages using Voodoo, or a Christian miracle-worker entering the Dream Time, and so on.
The Whateley Universe tries to be consistent about this. Given that the major characters now include a mage who is part Sidhe, a half-demon who has psychic abilities but deals with magic regularly, and an Action Girl with a magic sword, keeping the details consistent across authors must be fairly involved.
One story has a character begin to talk about a phenomenon that underlies everything in the universe which is what gives her her powers, only to be told by the other characters that it doesn't exist, or at least, they've seen absolutely no evidence of it. It's a nice thought at how theories are subjective, so when a character explains their own or someone else's powers, they could just be completely wrong yet still come up with an explanation that covers the bases.
Part of what helps keep the Whateley Universe canon stories straight is the secret "Whateley Academy Universe Bible" that only canon authors are allowed access to — this lays out every single "rule" for the storyline, canon characters, backstory, etc etc.
And, for another one of those 'secrets'...It's not been updated in about three years or so.
However it does play looser with acquisition of powers; Phase got his via some sort of virus that was non-contagious and nobody else displays any other form of symptom and Tennyo got hers via what are best described as Magic Screw The Rules I Have Plot Brownies.
The Slender Man Mythos is an interesting example; the character is shared between several projects by different groups, and one of the reasons he's so effectively frightful is that the most well-known Slenderblogs and vlogs keep things consistent. There's still wiggle-room for variation without angering the fandom, though: In Marble Hornets, audio and video distortions show up when something bad is about to happen, whereas in Everyman HYBRID, video usually doesn't distort unless Slender Man himself is both in the shot and very close to the camera.
Bending in Avatar The Last Airbender and The Legend of Korra mostly follows this. Certain characters can use various martial arts derived movements to telekinetically control one of the classical elements. It is possible to utilise this basic mechanic for more esoteric uses; e.g. "Bloodbending" is the act of a waterbender controlling the water in someone's blood, and by extension the blood in all of their bodily tissues. "Metalbending" is the act of an earthbender controlling the leftover impurities in metal to indirectly bend metal. Strong firebenders can generate lightning. As of The Legend Of Korra, it's shown that the characters are still learning and developing their understanding of these rules: Metalbending was only discovered in the original series by Toph due to her Disability Superpower, but is now understood enough to be taught to others and also to be defended against: platinum was found to be free of the impurities needed to bend it. Likewise, bloodbending was once thought to require a full moon to boost a waterbender's power, but people have been found that are powerful enough without it.
Lightningbending does show something resembling internal inconsistency in the final episodes, though. Supposedly it can only be generated by a firebender who can clear his mind of emotion and distraction—something the internally conflicted Zuko finds himself unable to pull off. However, in the end Azula seems to have no difficulties wielding it even while in the middle of emotional turmoil. Either she's just that good (she is a prodigy that bends hotter blue flames), the power-boosting Comet of Doom in the sky had something to do with it, or she has no internal conflict at all about being a psychotic sociopath.
Fire produced by firebending doesn't seem to work in the way real-world fire does; it has concussive force, and can burn in the air without fuel. Still, it is portrayed consistently, if not realistically.
Combustion Man's "sparky sparky boom" ray, which allows him to focus his firebending to an extreme level, is a power that he was born with, according to the Nickelodeon site. It also appears that it is that only form of firebending he is capable of.
Firebending appears to operate under different rules than other forms of bending. One that bends elements of earth, water, and air does so by manipulating existing matter. Firebenders, however, appear to create fire out of thin air. Despite this, it is still accepted since it is consistent in and of itself.
The Live-Action AdaptationThe Last Airbender attempted to remove the above inconsistency between the schools of bending by requiring firebenders to carry with them a source of fire to bend. In forcing firebenders to adhere to the same rules as other benders, however, the film utterly ruined the Fire Nation as a credible threat, thus proving that violating this trope isn't necessarily a bad thing.
Even Ty Lee's chi blocking, which appears to come out of nowhere with no explanation, is actually based off of the idea that acupuncture can block chi, and that bending uses chi as well.
One interesting aspect to note: According to the Grand Finale, it's implied that ALL bending arts are derived from Energybending, the most basal form of Bending. Before the arrival of the Avatar and the separation of the four elements, people bent the energy within themselves. At some point, they discovered the elemental bending arts, and, over time, the knowledge to perform energybending was almost completely lost, with the exception of the Lion Turtle who passed it down to Aang. While it's made clear that the various bending abilities came from external sources (dragons, badger-moles, flying bison, and the moon), it's also made clear that Energy-Bending was taught, not learned in complete solitude. Given all this information, it is very likely that while the bending arts are mostly separate, like the various types of martial arts they may in fact all be related in some degree, and it's possible that the current bending arts may have even evolved from Energybending, developing in various new ways but always using the same or similar principles as a basis.
Beast WarsTransformers had the "Transmetal" subline, which was forced on them by virtue of being Merchandise Driven. Essentially the story goes that they had to destroy a doomsday device in orbit that was threatening them with Death from Above. The resulting "quantum shockwave" changed the bodies of Transformers on both sides, but due to budget (CGI models take a lot more effort to redesign then with traditional animation) only a handful of current characters were redesigned. To try and explain why some changed while others didn't, those who weren't altered were otherwise incapacitated in a repair chamber or something else. It wasn't perfect though, there was still a few inconsistencies with a couple of characters.
The Transmetal process was refered to again. A device from the same aliens that sent the "Planet Buster" emitted a paralyzing pulse at the transformers around it. Those who with some form of transmetal in them proved to be immune to its effects. And even later in Beast Machines, a planet-wide virus on Cybertron incapacitated anyone who didn't change and those who did have a transmetal form reverted into their first forms. While it had some nasty side-effects such as memory loss and the inability to transform, that ended up being what saved them from certain capture.
The Fairly OddParents has consistent rules for making wishes, except in The Movie there is a magic muffin that allows a certain amount of unrestricted wishing for those trusted with it. The only wish that can't be made is for the magic muffin to taste better (yeah, the muffin is all powerful, but it tastes horrible).
Genies can also break the rules, though it might not be wise to go for it. The reason for this is that "Da Rules" aren't inherent to magic, but rather more like an unbreakable code of law for fairies; in at least one case, they actually had to add a new rule because Timmy screwed things up in a way that wasn't anticipated.
Mighty Max established how the portal system works that Portal A leads to Portal B and vice-versa. In order to travel the world they need to move through a series of portals to arrive at their destination, almost like a subway train map. In multiple episodes they show that the portal underneath Max's house leads directly to Skullmaster's cavern, and a portal overhanging a lava waterfall some distance away leads them to Australia, with the nearest portal on foot is 50 miles away.
In My Little Pony: Friendship Is Magic, magic can mostly do whatever suits the plot. However, Twilight Sparkle, an ardent student of the subject, insists that real magic has some rules. These are left vague, but she speaks of how it comes from within, and also how it is done consciously and studied. The closest thing to rules that appear in practice relates to there being different types of magic, which could be called Magic A, B, C, and a bunch of other letters.
Magic A is the obvious magic, unicorn magic. Every unicorn has some limited telekinesis for lifting small objects, plus a suite of spells related to their main talent; ergo, a unicorn whose cutie mark signified a particular skill for baking would have spells for getting dough to rise, batter to come together, what have you. Twilight Sparkle is unique in that her talent is the use and understanding of magic itself, so she can potentially learn any spell.
Unicorn magic is intimately tied to spells. Spells are something that can be read and learnt from books. It's not so clear what those books actually say, since the casting of a spell always involves nothing but mental effort and the unicorn's horn glowing. They are not external incantations; in the episode "Bridle Gossip", Twilight insist that there is no such thing as curses because curses are "artificial" and produced by external acts. However, the one spell we're given any detail about, Star Swirl the Bearded's unfinished masterpiece in "Magical Mystery Cure", is given as a rhyme (that doesn't rhyme), and the scene looks as if merely reading it out loud causes an effect, although the narration conflicts this somewhat. Go figure.
It's suggested (in "Magic Duel") that some specific effects are very difficult or impossible to achieve with (unicorn) magic, such as changing a pony's age or sex. It's also shown that an Amplifier Artifact can enable these up to a point.
Magic B is pegasus magic, mainly cloudwalking and weather control, plus some tactile telekinesis for towing things while in flight. Ducks also seem to be able to walk on clouds, so, you know, (shrug).
Magic C is the least obvious, earth pony magic. Earth ponies, according to Word Of God, have more strength and stamina than unicorns or pegasi of similar physique, and have an innate connection with the earth; so, for example, a farm run by earth ponies would outproduce a farm run by unicorns if all else were equal, simply by virtue of being tended by earth ponies. This also applies to magical crops, such as the Zap Apple.
She also has "Pinkie Sense", an ability to foretell upcoming events by various twitches and feelings in her body. It is precise and consistent enough for the residents of Ponyville to record and use them. It also only works for things in the near future, and has no consistency with any known form of magic at all, much to Twilight's frustration.
There's also her ability, or not, of Breaking the Fourth Wall. The fandom has taken this quite far, but Word Of God denies her having such abilities. What can mostly be observed in the series is a propensity to use the Aside Glance more often than other characters, and talking through the Iris Out at the end of an episode a few times. Interpreted through the denial of her having such abilities, the former is one of the weakest forms of Breaking the Fourth Wall and the latter might just be too silly to count as having actually happened in-universe. Anyways, the fans certainly like to take it further.
And then there's Magic D wielded by the Reality WarperMad God Embodiment of Disharmony Discord. It doesn't follow any rules, which is kind of the point, though it does conform to Twilight's maxim about magic stemming from within.
As of Season 3, there is also Magic E: Dark Magic. It was initially used by King Sombra and Princess Celestia, but Twilight was able to copy it to a limited extent. It seems completely designed to corrupt and inflict suffering, as it caused Twilight physical pain when she used it. King Sombra's singed, red horn might also be a hint that his overuse of it literally burned his horn away.
In a show with a name like this, one must not forget Magic F: the magic of friendship. It's not just figurative; in fact, it's about the most powerful kind of magic. In general, emotions can be used to power magic — not always in a positive sense.
The Elements of Harmony are "the most powerful magic known to ponydom", an Ancient Artifact set consisting of the elements of Honesty, Kindness, Laughter, Generosity, Loyalty, and Magic (ie. Friendship, because, after all, see show title), and powered by those things in the hearts of the ones wielding them. They unleash a Care Bear Stare that can defeat just about any evil.
The ponies themselves apparently have an inbuilt power to unleash a "Fire of Friendship" that keeps them warm and burns evil creatures, powered by love and friendship and channeled through a unicorn pony. This plays a part in the story of the founding of their country Equestria, as seen in "Hearth's Warming Eve".
It's also possible for an evil Emotion Eater to do the converse and feed on emotions, as with the Windigos feeding off on hate and the Changelings gaining power by draining a being's love for another.
The Crystal Empire can radiate emotions either positive or negative all over Equestria. They have a special Crystal Heart for focusing the emotions.
And then there are all kinds of miscellaneous magic on top of this.
The zebra Zecora is able to use magic too, somehow, though she doesn't seem to have any internal power like a unicorn. She can certainly brew potions that can do just about anything, and she is good enough to teach Twilight Sparkle about magic, which also implies that she uses some of the same principles as unicorns.
The Poison Joke is a plant that can cause humorous curses on anyone treading in it. Except, you know, they're not curses because there's no such thing, but apart from that.
Harvesting Zap Apples requires following a set of bizarre rituals worked out by trial and error that work for no apparent reason other than, "Magic is just funny that way."
Dragons have their own weird rules that aren't exactly normal physiology. For example, greed can make one grow.