These are the external factors needed to make a spell or [[RitualMagic ritual]] work. They fall under five main categories.

* [[CelestialDeadline The right time]]--when the [[{{Lunacy}} moon is full]], the summer solstice, an [[TotalEclipseOfThePlot eclipse]].
* [[PlaceOfPower The right place]]--somewhere mystically significant, such as Stonehenge or a place where two or more {{Ley Line}}s intersect.
* The right target--spells that only work on werewolves, or people wearing red.
* The right caster--spells that can only be cast by someone genuinely happy, or on the brink of death.
* The right [[CurseEscapeClause condition of negation]]--[[FantasticFragility spells that only work if there is a way to undo them.]]

They range from difficult to completely impossible for the caster to control. Persuading the target to wear red is fairly easy; making the sun set on command is beyond most wizards' powers.

Spells that only work at the right time serve to control the pace of a plot. If the BigBad can only cast the ultimate spell of world domination on one specific night, that both gives the heroes a deadline and explains why the BigBad didn't conquer the world ages ago. Spells that only work in the right place lead to battles for control of the key sites.

[[FunctionalMagic Inherent gifts]] are another common form of prerequisite; the spells only work for people born with the right talent.

See also SpellConstruction, PowerSource and InsertPaymentToUse.

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!!Examples:
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[[folder:Anime and Manga]]
* The Contractors from ''Anime/DarkerThanBlack'', who are required to perform Remunerations whenever they use their powers, lest they suffer from PowerIncontinence. These Remunerations range from smoking to eating boiled eggs to writing poetry to breaking a finger to drinking the blood of children, and a Contractor doesn't exactly get much choice in which one comes with their powers.
* A number of spells in ''Manga/NegimaMagisterNegiMagi'' require that the magic of TheWorldTree be active in order to work, such as [[spoiler: the spell the the festival arc's BigBad attempts to use to break TheMasquerade.]]
* In ''Manga/YuGiOh'', Yami's power can only be activated through games. If his opponent loses the Shadow Game, he is free to dole out magical punishment.
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[[folder:Films -- Animation]]
* In ''WesternAnimation/TurningRed'', the red moon ritual only works during a lunar eclipse and if the person undergoing the ritual is within a chalk circle.
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[[folder:Film -- Live-Action]]
* ''Film/TheMask:'' The titular MaskOfPower ''only'' works at night, apparently because Loki was a night god. Oddly enough,[[WesternAnimation/TheMask the cartoon]] features no such limitation.
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[[folder:Literature]]
* In ''Franchise/HarryPotter'', the brewing of Polyjuice Potion involved particular parts of a lunar cycle. Indeed, since Astronomy is a basic class celestial phases are probably involved in many kinds of magic; we just aren't given the tedious details.
** Also, it's stated that a certain mindset is needed for certain spells, particularly hatred for the Cruciatus and Killing Curses.
** And the Patronus charm, where the caster must be thinking of the happiest thought they can muster, which, given the circumstances of using the charm (being attacked by an EmotionEater), is no easy task.
** Magic in general can only be done by wizards. Give a muggle a wand and instruct them on how to cast a spell and they'll fail.
* In ''Literature/TheMagicians,'' the effectiveness of spells vary depending on numerous factors (phase of the moon, the weather, etc) that students at [[WizardingSchool Brakebills]] have to memorise. The fourth year at [[MysteriousAntarctica Brakebills South]] is dedicated to ensuring that the graduating students can act on these factors without even thinking about it.
** Also, magic has to be practiced with a relaxed and stable mind, otherwise a particularly spectacular MagicMisfire will occur.
* ''Literature/TheDresdenFiles'': In ''Blood Rites'' Murphy asks Harry why he just doesn't do the "pocket full of sunshine" trick on the [[OurVampiresAreDifferent Red Court vamps]]. He states it turns out you have to be genuinely happy to make the spell work.
** More generally, no act of magic can be performed if the caster doesn't ''believe'' that it is an appropriate course of action. So if you don't ''believe'' that setting someone's face on fire is a good idea, you won't be able to do that (on purpose).
* ''Literature/JonathanStrangeAndMrNorrell'': Many spells only work while the "King's Roads" are active.
* This is the main limitation of magic in Rick Cook's ''Literature/WizBiz'' series. The more powerful the spell is, the more prerequisite it has and the more likely it is to fail or do something completely different if the prerequisites are not filled.
* The 'negation' angle comes up in the Literature/{{Discworld}} novel ''Literature/{{Sourcery}}''. A wizard seeks to escape Death by sealing his soul inside his wizard's staff. Death tells him no deal, unless there's a condition that causes his soul to be released (because ''nothing'' escapes Death.) The wizard offers to let his soul be freed if his son willingly tosses aside his staff. Death accepts.
** Well, his first suggestion was "when hell freezes over", but Death shut him down.
* Subverted in ''Literature/TheElenium''. Sephrenia makes a huge deal about how magic spells must be cast in Styric, not Elene, but later it is revealed that this is because the spells are actually prayers directed at each Knightly Order's patron deity. Sparhawk speaks Elene to Aphrael on several instances when requesting magic be done, and she complies with no issues. Likewise, the Bhelliom is shown responding to Elene, Styric, Tamul, and even Troll.
* In ''Literature/{{Athyra}}'', as Vlad decides to teach someone some of the basics of witchcraft, he mentions 'Places of Power'; practicing magic tends to be easier (particularly if it was created by someone performing magic there).
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[[folder:Live Action TV]]
* This is the only thing that keeps the universe of ''Series/BuffyTheVampireSlayer'' from ending, since all the [[BigBad BigBads]] that want to [[TheEndOfTheWorldAsWeKnowIt destroy the world]] have to wait their turn and go to [[CityOfAdventure Sunnydale]], where the [[{{Hellgate}} Hellmouth]] resides, and where [[UltimateShowdownOfUltimateDestiny they have to face]] the [[TheHero Slayer]].
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[[folder:Tabletop Games]]
* The cantrips of ''TabletopGame/ChangelingTheDreaming'' had bunks, little obligations to the Dreaming that would make using a certain ability easier. Want to fly? Burn an eagle's feather, or tap your foot three times. Want to talk to rocks? Paint a little sigil on them. The more complex the bunk, the more likely the cantrip is to succeed.
* ''TabletopGame/ChroniclesOfDarkness'':
** ''TabletopGame/ChangelingTheLost'': Each [[MagicByAnyOtherName Contract]] has a specific Catch. By performing the Catch, the changeling avoids spending Glamour to activate the Contract. These Contracts range in applicability from "You must be fighting multiple foes, bare-handed, by yourself" to "You must use this power within five minutes of noon" to "Your target must be wearing or touching gold."
** In ''TabletopGame/MageTheAwakening'': {{Summoning Ritual}}s impose extra conditions, unlike conventional spells:
*** Supernal entities can only be summoned by a mage whose [[MagicAIsMagicA Path]] matches the entity's home realm, and impose some kind of trial as part of the summoning. For example, to summon a spectre from Stygia, a {{Necromancer}} might have to prepare gifts that remind it of what it means to be alive.
*** [[BlackMagic Abyssal entities]] can only be summoned at a location [[EvilTaintedThePlace tainted by evil and harm]] that match the spirit's area of influence, using similarly corrupt implements. A lesser {{Familiar}} only comes for someone who destroys a SpellBook with a piece from a [[TheTower fallen tower]], whereas the [[LivingShadow Darkness that Thirsts]] requires a lightless place where atrocious human suffering has been concealed.
** ''Immortals'': Under the rules of EquivalentExchange, [[BloodMagic Blood Bather rituals]] can be [[SpellCrafting designed]] with more stringent conditions for greater benefits. A ritual that requires multiple {{Targeted Human Sacrifice}}s, a full {{Cult}} ceremony, a marble tub, precious unguents, and the night of the winter solstice generates more metaphysical oomph than a quick dousing of animal blood.
* ''TabletopGame/DungeonsAndDragons'': Several {{cursed|Item}} (or in this case unreliable) items have [[http://www.d20srd.org/srd/magicItems/cursedItems.htm prerequisites]] that would render then practically useless, others just need to be used in the dark or by a certain gender.
* There are a number of spells in ''TabletopGame/MagicTheGathering'' that can only target creatures of a certain color; more commonly, creatures will have "protection from [color]," preventing them from being harmed by creatures or spells of that color. Finally, there are some spells that can target anything-''but''-color; this is mostly [[AmbitionIsEvil Black]] being unable to destroy other Black creatures, [[FridgeLogic possibly symbolizing]] how Black can be its own worst enemy.
* ''TabletopGame/WarhammerFantasyRoleplay'': RitualMagic can surpass the limits of normal spellcasting but has more stringent prerequisites, [[EyeOfNewt ingredients]], and [[MagicMisfire consequences for failure]]. Vampires can only be resurrected on UnholyGround; the [[MysticalPlague Neiglish Rot]] can only be inflicted by a spellcaster who has survived it; a SterilityPlague can only target a bloodline with no currently pregnant members; and so on.
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[[folder:Video Games]]
* ''VideoGame/WarcraftIII'' has several spells with targeting restrictions.
** Most magic buffs and debuffs don't apply to mechanical units. Except, for some reason, Inner Fire, which increases armor and damage, and thus is often seen on the already hard-to-kill [[BatteringRam Siege Engines]].
** The Tauren Spirit Walker has the Ancestral Spirit spell which brings back a dead Tauren from the dead. Naturally, this only works on units classified as "Tauren", leading to major GameplayAndStorySegregation in Rexxar's campaign where centaurs (who are something of an EvilCounterpart to the tauren) were classified as such as one of their spellcasters had the same spell.
** InUniverse with the revival of Kel'thuzad in the pool of mystic energy called the Sunwell (requiring the destruction of the high elf kingdom to reach it) and the summoning of Archimonde at Dalaran, requiring the use of a magical artifact and Kel'thuzad channeling magic for half an hour.
[[/folder]]

[[folder:Western Animation]]
* ''WesternAnimation/AvatarTheLastAirbender'':
** Bloodbending requires a power boost from the [[{{Lunacy}} full moon]] ([[spoiler:unless you have the proper genes to bloodbend whenever you want]]). Explained by the moon being the power source for waterbenders, of which bloodbending is a complicated form.
** On a variant, there is ten-fold amplification of firebending that allows for grand conquest only happens once every hundred years - Sozin's Comet. Whether conditions exist that would amplify air or earthbending ([[FridgeLogic and why a comet would amplify fire and not earth or water]]) is open to speculation.
** On a similar note, the various forms of Bending and the way they affect their respective cultures tend to breed different ways of looking at the world; in order to master any given form of Bending, Aang has to learn to think like its practitioners. Earth gives him particular trouble because the forceful, head-on approach of the Earthbenders is the polar opposite of the Zen, understand-all-angles approach he was raised with as an Airbender.
** In a similar vein, Korra in [[WesternAnimation/TheLegendOfKorra the sequel]] has already mastered three of the four elements but has a mental block when it comes to Air because she is a HotBlooded person who likes to face challenges head-on. She also cannot tap into the Avatar state because of her lack of spirituality.
** As the bending disciplines are stronger at certain times, so is there an off switch. Where there is a solar eclipse, firebenders lose their powers. The other elements' weaknesses are not known. (Yes, you'd think waterbending's a no-go during the new moon, but that's never stated outside the realm of fanfic).
** Metalbending is apparently less bending the metal itself and more the impurities in the metal (e.g. if you interpret steel as iron and charcoal). Platinum, for whatever reason, is immune to this.
* In ''WesternAnimation/{{Gargoyles}}'', magic works easier if there is a defeat condition built into it (Gargoyles were mystically turned to stone until the castle rose above the clouds, humans would continue to turn to stone at night until the sky burned with fire, etc). The conditions tend to be hard, but not impossible, tasks. Magic requiring it is the justification for the CurseEscapeClause trope being in effect when no BigBad would ever create such a condition. [[TheFairFolk The third race]], being magically powerful by nature, rarely bother with such conditions.
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