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Circular Reasoning

This image is true because it agrees with this image.

Attorney General: Brawndo's got what plants crave.
Secretary of Energy: Yeah, it's got electrolytes.
Joe: What are electrolytes? Do you even know?
Secretary of State: It's... what they use to make Brawndo!
Joe: Yeah, but why do they use them to make Brawndo?
Secretary of Defense: 'Cause Brawndo's got electrolytes.

Begging the Question used recursively. A is true because B is true. B is true because C is true. C is true because A is true. The proof simply circles around and around, with nothing in it that isn't being proved by itself. This is a logical fallacy, because it disallows the possibility that all three are false and, like Begging the Question, presupposes the truth of the thing it's supposed to be providing an argument to prove the truth of. To summarize, the one using it thinks that their claim proves itself.

If A, B, or C has independent proofs that are "outside the loop," it is no longer circular reasoning.

The simplest form of this is a tautology; see also Shaped Like Itself and Famous for Being Famous.

Looks like this fallacy, but isn't.

• Algorithms that describe decision-making processes often loop back to the decision point, but being decisions they have more than one possible circle. These algorithms, while circular, describe a process rather than making an argument.

Examples:

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Fan Fic
• Directly invoked by the narrator in Equestria: A History Revealed, in which she states that if Celestia was willing to lie about the Hearth's Warming Eve Paegent first, then she would be willing to lie about the Hearts and Hooves Day legend too, as she would have experience in lying. But if she lied about the Hearts and Hooves Day legend first, then she would clearly also lie about the Hearth's Warming Eve Paegent, as it held much greater significance.

Film
• Invoked in Idiocracy by the Presidential Cabinet members when Joe fruitlessly tries to explain to them why they should stop watering crops with Brawndo (a sports drink):
Attorney General: Brawndo's got what plants crave.
Secretary of Energy: Yeah, it's got electrolytes.
Joe: What are electrolytes? Do you even know?
Secretary of State: It's what they use to make Brawndo.
Joe: Yeah, but why do they use them to make Brawndo?
Secretary of Defense: 'Cause Brawndo's got electrolytes.
• Clue: The blackmail against Mr. Green is that he's gay. He has no issue with it himself, but he'd be fired if his employers (the State Department) found out because they'd view him as a security risk... which he is solely because of that policy. His stating such is met with a quick beat.
• Bill and Ted wish fervently for their band The Wyld Stallyns to become famous. However, they disagree on how they should make this happen:
Bill: The truth is, Wyld Stallyns will never be a super band until we have Eddie Van Halen on guitar.
Ted: Yes, Bill. But, I do not believe we will get Eddie Van Halen until we have a triumphant video.
Bill: Ted, it's pointless to have a triumphant video before we even have decent instruments.
Ted: Well, how can we have decent instruments when we don't really even know how to play?
Bill: That is why we need Eddie Van Halen!
Ted: And that is why we need a triumphant video.
Bill and Ted: EXCELLENT! (air guitar solo)
• Erik the Viking: "Well, if the only reason for the expeditions is the looting and pillaging, and the only reason for the looting and pillaging is to pay for the next expedition, then that's a circular argument, isn't it? They cancel each other out."

Literature
• The Catch-22 of the novel of the same name is Circular Reasoning. The dialogue that explains it:
Yossarian: Is Orr crazy?
Dr. 'Doc' Daneeka: Of course he is. He has to be crazy to keep flying after all the close calls he's had.
Yossarian: Why can't you ground him?
Doc Daneeka: I can, but first he has to ask me.
Yossarian: That's all he's gotta do to be grounded?
Doc Daneeka: That's all.
Yossarian: Then you can ground him?
Doc Daneeka: No. Then I cannot ground him.
Yossarian: Aah!
Doc Daneeka: There's a CATCH!
Yossarian: A catch?
Doc Daneeka: Sure. Catch-22. Anyone who wants to get out of combat isn't really crazy, so I can't ground him.
Yossarian: Okay, let me see if I've got this straight. In order to be grounded, I've got to be crazy. And I must be crazy to keep flying. But if I ask to be grounded, that means I'm not crazy anymore, and I have to keep flying.
Doc Daneeka: You got it, that's Catch-22.
• The Little Prince encounters a tippler on his way to Earth. When asked why he drinks, the tippler explains that he wants to forget. When asked what he wants to forget, he says that he wants to forget that he is ashamed. When asked about that, he explains that he is ashamed of drinking.
• In Nomes Trilogy (about a certain almost insignificant subset of living things of Florida):
But they're the ones who matter. At least, in their opinion. And their opinion is the one that matters. In their opinion.
• Rudyard Kipling nodded at it in a darkly humorous way in "The Sleepy Sentinel" (Epitaphs of the War):
I sleep because I am slain. They slew me because I slept.
• In Jingo, the long-lost island of Leshp resurfaces in the sea between Ankh-Morpork and Klatch. Both nations have been at peace for decades and have no reason for conflict, but because Leshp is in such a strategic position and would be a natural staging point for a conflict, they can't afford to let the other country possess it.
Vimes: So we're supposed to go to war over some rock that's only useful if we have to go to war?
• In Making Money, this is why The Department of Post Mortem Communications can't be called necromancy:
Moist: So what you are saying is that necromancy is a very bad form of magic performed only by evil wizards, and since you are not evil wizards, what you are doing cannot possibly be called necromancy?
Dr. Hicks: Yes.
Moist: And what defines an evil wizard?
Dr. Hicks: Well, for a start, doing necromancy.
Moist: And because you're not evil wizards, what you're doing can't be called necromancy.
Dr. Hicks: Exactly!
• In Starfighters of Adumar, Wedge points out the use of this trope as he takes apart the concept of a Proud Warrior Race Guy:
Wedge: Circular thinking. I'm honorable because I kill the enemy, and I kill the enemy for the honor. There's nothing there, Cheriss.
• The "Gay people cannot have Government jobs, because they're a security risk, because they could be blackmailed, because gay people cannot have Government jobs" policy listed under Real Life is described by Roy Tappen in The Leaky Establishment by David Langford. In a reducto ad absurdum analogy, Tappen points out that if the security men start with "we find this behaviour suspicious", you can apply the same logic to anything. Drinking vodka, for example.
• The same policy is played with in The Laundry Files, where the Laundry bosses are more logical. Pinky and Brain are required to attend Pride every year, thereby proving that their sexuality is not a secret that could be held over them.

Live Action TV
• A sketch on That Mitchell and Webb Look had a group of government agents justify covering up the Roswell incident in this way. They could release all the information now in order to gather support and build defences against a possible invasion, but people will be angry with the government when they learn that aliens exist, especially if there is an invasion and it turns out that the government knew about them for decades but did nothing to help gather support and build defences.
• In The Twilight Zone episode, "Five Characters in Search of an Exit," when the major pounds on the wall, the clown sings, "We're here because we're here because we're here because we're here."note
• Monroe's dad in Grimm when he learns his son's marrying a Fuchsbau. This starts a huge argument, during which Bart starts ranting that mixed marriages destroy families: "It's happening already!" In other words, he disapproves of Monroe marrying Rosalee, because they're having an argument, because he disapproves of Monroe marrying Rosalee.
• In the Porridge episode "Rough Justice", Judge Stephen Rawley, convicted of corruption, gets out on appeal. Fletcher notes that Mackay is now calling him Mister Rawley (he only refers to prisoners by their surname).
Mackay: Certainly. If the appeal court judges say his nose is clean, that's good enough for me. They are men of the highest integrity in the land.
Fletcher: What're you talking about? He's one of them!
Mackay: Precisely. And he's innocent, which proves my point.
• Sherlock: Played for Laughs when Sherlock is scanning John.
Sherlock: You have a limp, which your therapist believes is psychosomatic—
John: How do you know I have a therapist?
Sherlock: You have a psychosomatic limp; of course you have a therapist.

• The Men from the Ministry: How does Mr. Lamb remember the to read the notes on the blotter? He has a notebook in which he writes notes to look at the blotter. How does he remember to look at the notebook? He has a reminder on the blotter.

Video Games
• In Ratchet & Clank: Going Commando, Ratchet and Clank come across a Circular Reasoning logic puzzle in the middle of nowhere inside of a desert cavern. The "puzzle" consists of using an upgraded wrench, currently encased in glass, to gain a rock which is also encased in glass, in order to break the glass containing the wrench. Clank is amused by the challenge and briefly tries to deduce how to solve it, but its obvious that since each requires the other, it's impossible without Taking A Third Option, which Ratchet does by using his own wrench.
• In Fallout 3 it's possible to take down President Eden by convincing it that it is using circular reasoning when it declares that it is infallible because it was programmed to be. This initiates a Logic Bomb that allows the player to convince Eden to self-destruct.
• Employed by the train robots in Broken Age. They need the "Young Hero" to save the runaway train. Because the Young Hero is the only one that can save them, the train doesn't start until the he arrives. The robots are thus completely horrified by Young Hero's disappearance, because then no one will save them. The issue is a little justified: they were built to entertain a kid eager for something exciting.
Vella: If the train isn't a runaway until your hero arrives, and your hero is missing, then what's the problem?
Train Conductor: If the Young Hero never arrives, then we have no purpose.
Robot #2: Do we even exist?!
Train Conductor: You see? Its unsafe from a philosophical point of view.

Web Animation
• On the Zero Punctuation review of World of Warcraft: Cataclysm, Yahtzee asked another player why he raids. The raider's reason is that it gets stuff. Why does he want stuff? To raid with.

Web Comics
• The Order of the Stick:
• Though she ultimately turns out to be right, Elan points out that Haley is using circular logic against Tarquin: She won't tell him that lives are at stake concerning the information she wants because she doesn't trust him, and she doesn't trust him because he's withholding information when lives are at stake. Haley is not pleased at having been out-logicked by The Ditz.
• Another instance, when Grubwiggler accuses the Thieves' Guild of robbing him even though he pays them protection:
Crystal: HEY! Our thieves are only allowed to steal from people our thieves are allowed to steal from!
Bozzok: My colleague's circular logic notwithstanding, she is correct.
• In The Non-Adventures of Wonderella: Wonderella and Dr. Shark use this when confronting an high school student about the dangers of marijuana:
Wonderella: Marijuana is illegal, young man.
Student: But, why?
Wonderella: Because it leads to harder drugs [...]
Student: Who says I have to try harder drugs?
Student: But why do I need to go to a dealer?
Dr. Shark: Because, young man, Marijuana is illegal.
• When Trawn of Electric Wonderland takes a shortcut to her Home Base through 4chan's domain, she learns from passers-by that everyone there keeps repeating certain Catch Phrases because they're humorous, those Catch Phrases are humorous because everyone there keeps repeating them, and everyone there keeps repeating them because they're humorous.
Trawn: Ugh, the logic here drives me crazy on normal days!
• Knowingly used in Basic Instructions.
Scott: "They were better, because they were superior." That's a good point, on account of its quality.
• In the xkcd "Every Major's Terrible" song, a theology major can be seen writing a proof that goes "X, therefore there exists X".
• Rose and Kanaya in Homestuck:
ROXY: so you are roses girlfriend right?
KANAYA: I Dont Know
KANAYA: Is That What Humans Call A Matesprit When The Matesprit Is A Girl
ROXY: umm
ROXY: i dunno
ROXY: is a matesprit the thing trolls call each other when they are girlfriends or boyfriends with each other?
KANAYA: Yes
ROXY: ah ha!
ROXY: then uh
KANAYA: Yes
• In Freefall, Florence is given a direct order to like the mayor, trust her, and want to make her happy. Much later, when asked if she wants the order canceled, she refuses, stating that she trusts the mayor and removing the order would not make her happy. It's removed anyway, on the grounds that she's "obviously hit a limit in self-diagnostics".

Web Original
• In Noob there seems to be little of this going on in Master Zen's situation and it comes up when Omega Zell gives him advice along the lines of "How about you stop harassing us and get yourself a hobby other than the MMORPG we're all playing?". Master Zen's reply can be paraphrased as "I can't keep myself busy with anything else than the MMORPG because I can't leave my hiding place. I escaped jail to be able to harass you guys on the game, remember?".

Western Animation
• During one Beavis and Butt-Head music video segment, Beavis asks why a certain person in the video is on TV. Butt-head says he's on TV because he's famous. What's he famous for? He's famous for being on TV. This goes back and forth for awhile, with Butt-Head getting increasingly irritated that Beavis doesn't get it.
• In the Jimmy Neutron TV movie, "The League of Villains", during a Kangaroo Court, T is upset that he has to be the court's bailiff instead of being on the jury with the rest of the villains. When he asks why he can't be on the jury, the villains tell him that they already voted on it. He asks why he didn't get to vote, to which the response is, "Because you're not on the jury."

Real Life
• A monarchy is a nation ruled by a monarch; a monarch is someone who rules a monarchy. What with Hereditary Republics, Elective Monarchies, and Presidents-For-Life, that's about the clearest definitions there are, and political scientists often admit that sometimes the only difference between a monarchy and a republic are the titles involved. Practically, it's the same: as someone wrote, "Romans noticed they had an Empire already only when the Court protocol changed".
• In practice, the usual definition of monarch is "ruler who gained his/her position by virtue of his/her bloodline", i.e. being the head of the nation's royal family. This distinguishes a monarchy (in which rulership is hereditary) from a republic (in which rulership is granted by a voting body). The question now becomes how the royal family gained the status of "royal family" in the first place, and the answer to that question can only be found in the very beginning of the civilization in question (or the most recent coup d'etat). Furthermore, either a monarchy or a republic can devolve into a dictatorship, the key aspect of that being a ruler seeking to gain, exert, and maintain effectively absolute power. (Many modern dictatorships are republics-in-name-only where elections are blatantly rigged so that only the current ruler has any chance whatsoever of winning (usually by means of anyone who doesn't vote for the current ruler being hunted down and slaughtered), Iraq under the rule of Saddam Hussein being a textbook example.)
• Fix point in mathematics (and (co-)induction). Circular reasoning done carefully enough to work.