When people go around using magic at random in fiction, certain laws are employed to explain how such magic works. This is particularly true of FunctionalMagic. It is not, however, true of PsychicPowers, and LeyLine magic, [[FunctionalMagic Theurgy, Force Magic, Alchemy]], and WildMagic may operate on different rules. Some constants, such as the law of Association, may still be true though (a person with PsychicPowers may be able to sense someone due to common traits).

These aren't the laws of the real universe; those are covered by science. Rather, these are quirks of human psychology. Magic that works by these laws will seem plausible enough (to a human audience) in a fictional work, and real-world human superstitions tend to take one of these forms.

This is not totally confined to fiction however, as some forensic rules also use these. For example, the Law of Association come under LocardsTheory, and anyone with a phone book prior to the age of cellphones would be using the Law of Names to look up someone's name and number.

Related to MagicAIsMagicA. And FunctionalMagic.

Not to be confused with the book series Literature/TheLawsOfMagic, despite the story using many of the below.

!The Laws
Most of these have been ripped wholly from [[http://www.themystica.com/mystica/articles/l/laws_of_magic.html this site]], which in turn took them from Isaac Bonewits' book Real Magic. Bonewits in turn took the Laws of Similarity and Contagion from Frazer's Golden Bough.

* The Law Of Knowledge: With understanding comes control and power. (This law is responsible for things like AwesomeByAnalysis).
** Law of Self-Knowledge: One who does not know himself, having never tested himself or his limitations does not know what he can do. And the reverse is also true. (This law is responsible for things like LiteralSplitPersonality, where other sides of self that are previously unknown come to light dramatically)
* The Law of Names: Related to both the Law of Knowledge and the Law of Association. The law simply states that by knowing the true and complete name of a phenomenon or entity gives you complete control over it (This law is responsible for things like IKnowYourTrueName).
** Law of Words of Power: Knowing the name of a phenomenon allows you to summon it. (This law is responsible for things like CallingYourAttacks).
* Law of Association: This law is the most commonly and frequently used of all the laws of magic. This states things react upon each other by their connection with each other (see LocardsTheory above).
** Law of Similarity: Like things produce like things, or that an effect resembles its cause (in other words, the ButterflyOfDoom and numerous other cause-and-effect tropes).
** Law of Contagion: This law states that things which have once been in contact with each other continue to act on each other at a distance even after physical contact has been severed (MachineEmpathy and TheEmpath are two examples, but there are many, many examples of this law).
** Law of Synecdoche (from the Literature/LordDarcy series) "the part is equivalent to the whole". An example would be using someone's hair to cast a spell on them. Often seen as a sub-part of the Law of Contagion.
*** Law of Identification (Imitation): Where one entity assumes the characteristics of another. The more the first entity knows about the second the better the imitation. Seen as a combination of Contagion and Similarity. (From which we get the {{Doppelganger}} trope)
** Law of Relevance: added to the Law of Contagion in the Literature/LordDarcy series. The effectiveness of the connection created by the Law of Contagion depends upon the relevance of the contact. For example, if only one person has ever worn a pair of shoes, it's easy to use the shoes magically to identify that person, because that person is very relevant to those shoes. However, identifying the last person to use, say, a house pair of bowling shoes is difficult or impossible, because that person has no special relevance to those shoes.
* Law of Opposites: The synthesis on two opposing or conflicting ideas or pieces of data will produce a new, third idea that will not be a compromise of the original two (YinYangBomb and FusionDance are examples).
** Law of Polarity: anything can be separated into two opposite parts with each part having its own essence (BlackAndWhiteMorality from GreyAndGrayMorality for instance).
** Law of Balance: One's energy or power level must be kept on an even keel, too much or too little will kill oneself (HeroicRROD is a good example).
* Law of Infinite Data: There always new information for one to learn. The sources of knowledge are limitless if one wishes to tap them. (GreatBigLibraryOfEverything or Cyberspace is a good source of infinite data)
* Law of Finite Senses: One's senses are finite. They are limited to the amount of information which one can absorb and process at any given time (This trope is responsible for YouCannotGraspTheTrueForm).
* Law of Infinite Universes: Each person sees his universe or world a different way; therefore, no two people have identical views of the world. (AlternateUniverse is the most obvious trope example, though this is from a universal rather than personal perspective).
** Law of Pragmatism: If it works, it's true (From this we get things like CombatPragmatist).
** Law of True Falsehoods: If it's a paradox, the paradox is probably true (LogicBomb is the most obvious example).

! Examples
* According to Jewish tradition, the Name of God (which is commonly written as YHWH, but there's supposedly a much longer version of this name only used by the Jewish high priest) is forbidden to be said, despite being being said liberally throughout ''Literature/TheBible''. This is definitely part of the Law of Names, and is likely due to fear of misuse or simply turning the name of God into a mundane word.
* ''Literature/TheDresdenFiles'': The title character uses the Law of Contagion as a basic crime-solving technique.
** He used the Law Of Infinite Data to send Ivy a message on one occasion. The Law of Names is also frequently used or mentioned in the series.
* Ironically, these laws in regard to FunctionalMagic are largely averted in fantasy due to a combination of the fact that the [[SmallReferencePools full list of laws is]] [[GeekReferencePool somewhat obscure]], with the exception of the Law Of Knowledge (basically in order to use magic someone has to know enough to use it), the Law of Names (in works where IKnowYourTrueName is in play), the Law of Words of Power, and the Law of Balance (mainly just used because otherwise people cast spells one right after another with no fatigue or anything).
** Even the Law of Knowledge is sometimes ignored, in cases where the person doesn't know he has magic powers uses them without meaning to. Like Harry Potter shrinking the horrible sweater, or teleporting away from the bullies, or freeing the snake.
* Terry Brooks' ''Literature/{{Shannara}}'' series frequently uses Law of Balance. Basically, the idea is that magic used up takes its toll on the body, and using more than the body has (well, it produces [[TheHeartless Shadowen]]).
* Every fantasy setting created by Creator/HarryTurtledove uses two fundamental laws of magic, the Law of Similarity (two similar-looking things have a magical link) and the Law of Contagion (two things that have touched have a magical link). Examples include ''Literature/{{Videssos}}'' and the ''Literature/DarknessSeries''--in the latter, [[FantasticScience research mages]] discover a new fundamental connection between the two laws, which allows them to create a FantasticNuke.