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"I live by syllogisms: God is love. Love is blind. Stevie Wonder is blind. Therefore, Stevie Wonder is God. I don't know what I'd believe in if it wasn't for that."
"Logic, my dear Zoe, only allows one to be wrong with authority."
Logic. Every story needs it, unless you just want a series of unconnected images and no plot to speak of.
But the problem is, logic requires writers to think pretty hard about what they write, and not all writers have time for this. As such, they take shortcuts which at best can lead to Plot Holes, and at worst undermines the entire story. Most Straw Vulcans suffer from this, following the author's flawed view of what is logical. (For one thing, much of the time they say "logic" when they mean "rationality"; they aren't the same thing at all. But even when they get that much right, they still frequently fall into the errors listed below, or have their "logical" characters do so.)
Other times, writers deliberately invoke this, to make their characters more human, or to explain why they didn't take the best choice.
For examples of writers intentionally or unintentionally failing logic forever, see Insane Troll Logic.
Not to be confused with Logic Bomb.
Types of fallacies and examples
- False dilemma
 — Portraying a problem as having only two solutions. For example, telling someone "either you stop eating ice cream or you will get fat" — this ignores that there are other ways of losing weight, such as exercise, or giving up foods other than ice cream. Commonly invoked to set up a Friend Or Idol Decision or The Sadistic Choice. Subverted whenever a character Takes A Third Option.
- A common version of this is to assume that only the extreme ends of a scale are possible, without considering intermediate positions. For example "You're either with us or against us" or "If you're not part of the solution, you're part of the problem". See False Dichotomy.
- Classic examples of this include such gems as "Do you like Kirk or Picard?" "Do you like drama or comedy?" and the particularly tenacious "Do you believe in science or faith?" These things and more are magnificent examples of attempts to force a person into choosing between two things that are entirely compatable.
- Argument to moderation — In some sense the opposite of a false dichotomy, assuming that the extreme ends of the spectrum are necessarily wrong and the best option must lie somewhere in the middle:
Bob wants to kill all puppies in the world.
Alice doesn't want to kill any puppies.
Therefore, we should compromise and kill 50% of all puppies.
Belkar: See, now that's what being on a team is all about. You didn't want to kill any hobgoblins. I wanted to kill all the hobgoblins. So what did we do? We compromised, I killed one of the hobgoblins.
- Begging the question — "Proving" that something is true by supporting your argument on facts that are only assumed to be true.
Alice says she didn't kill Bob.
Alice would never lie.
Thus, Alice didn't commit murder.
- This phrase is commonly misused to mean "leading inevitably to the question" despite purists pointing out that this is not the original meaning. "Beg" in this instance is really a shortened version of "Beget."
- Because the phrase "begging the question" can be used outside an accusation of fallacy, this is often referred to by its Latin name, petitio principii in more formal settings.
- [This discussion, off topic though it is, would not be complete without explicitly noting that to educated persons, "begging the question" is always an accusation of fallacy.]
- Sharpshooter fallacy — A way of fiddling statistics where you change the conditions until you "prove" what you want. The prototypical example is of a person shooting a gun at a wall, painting a target around the bullethole, and claiming to have scored a bullseye.
- Anyone who claims to have found codes in The Bible or Shakespeare has more likely than not committed this one, since finding the codes involves trying every combination of letters until a message that suits your particular type of eschatology/authorship appears, and ignoring all the times that it does not.
- Likewise with all those claims of how various people's names are secret encodings of the Number of the Beast, 666.
- Mentioned on NUMB3RS, but the accusation proves to be invalid.
- Moving The Goalposts (also called Raising The Bar) is closely related to the Sharpshooter Fallacy, but instead of you setting your goal wherever you want, you insist that your opponent must make a new argument, meeting a more restrictive set of requirements, each time he succeeds in proving his case.
- In one noteworthy case in the field of Geophysics, what seemed to be an extraordinary claim was made by Louis Frank in 1986: dozens of house-sized ice comets were hitting the Earth's atmosphere every minute. Most of the community of geophysicists dismissed it out of hand, but Clayne Yeates decided to test it, booking time on the Spacewatch Telescope on Kitt Peak in 1988. To his surprise, he succeeded in getting photographs that showed exactly what Frank had predicted. The normal standard for publication is two photos (not necessarily consecutive) clearly showing the same object. But when Yeates submitted his findings and photos to Geophysical Research Letters, a respected, peer-reviewed journal in the field, he was told in a letter that his paper would only be accepted if he had consecutive pairs of photos, clearly of the same object. He resubmitted the paper, including six such sets of paired photos. And then he was told by the reviewing panel, "Oh, no, we need THREE consecutive photos before we'll publish it." There's no reason to believe that if he had had three such photos they wouldn't have demanded four, and so on. The editors moved the goalposts.
- Are you listening, Judge From Ace Attorney Games?
- Gambler's fallacy — believing that dice/coins have memory: if a coin has just landed on heads four times in a row, surely it's much more likely to get tails this time, to even things out... or alternatively, heads is on a roll and will appear next time too. See also Random Number God and You Fail Statistics Forever.
- In fact, if you toss a previously untested coin and (say) heads come up, there's a larger chance to get heads on a second roll, because the coin might be biased.
- A Darths & Droids strip covered this one, with one player having a carefully prepared 20-sided die that had previously rolled two ones — the chances of rolling 3 ones in a row is only 1 in 8000, so surely another one is almost impossible, right?
- By now, the die is rolled. It's a 1; Qui-Gon dies.
- Pete's answer (the one who prepared the die)? "Awesome! That die will be even luckier next time!"
- Any Warhammer gamer or tabletop roleplayer will tell you that this is absolutely true.
- Discussed at length in Rosencrantz & Guildenstern Are Dead, in which Guildenstern flips eighty-five coins in a row that all come up heads, but suggests that it shouldn't be surprising since each coin has an equal chance of coming up heads as tails.
- The chance of this series happening (with unbiased coins) is one in 38 septillion (that's million million million million), in case you are wondering. See the next point for clarification.
- Psychologically this fallacy tends to come from the fact that the odds to replicate a pattern do go up cumulatively. The odds of rolling 20 on a d20 twice is 1/400. The odds of rolling the first is 1/20, and the odds of rolling the second is also 1/20. The fallacy occurs when someone attempts apply the full cumulative odds to the next roll. Similarly the odds of rolling a 5 and a 17 on a D20 in that order are also 1/400, so that number's pretty irrelevant.
- Another factor is that many people confuse "a number of independent events" with "a series of independent events". Flipping a coin once gives me a 50% chance of getting heads. Flipping it a second time, I still have a 50% chance of getting heads. They're independent events, and there happens that there are two ("a number") of them. No matter what the number is, they remain separate independent events. But if I pick up the coin and say, before I flip it at all, "I'm going to flip this coin twice. What are the chances of my flipping two heads in a row?" the answer is that I have a 25% chance. I am not looking at two independent events but a specific series of events — a head and then another head. There are four ways the flips can come out: Heads-heads, heads-tails, tails-heads, and tails-tails. Only one of the four is the series specified.
- Post Hoc, Ergo Propter Hoc (After this, therefore because of this) = Correlation implies causation — claiming that because two things are correlated, one must cause the other. The truth can be that the correlation is coincidental, or that both things are related to a third thing, which is itself known as the Third Variable Problem.
- Pastafarianism claims that pirates prevent global warming, as the number of pirates is decreasing while temperatures increase.
- This xkcd strip using the rise of both Firefox and Wicca to imply that Firefox causes witchcraft.
- One episode of Justice League features a journalist claiming that since white-collar crime has risen since the League formed, the League clearly causes that crime. (In fact, given the League's style, it's entirely possible that the smarter criminals turn to white-collar rather than blue-collar crime to reduce the chances of Superman slapping them around Metropolis, but his logic still doesn't track.)
- The irony is that the Justice League is funded, in large part, by funds siphoned off from Wayne Enterprises by Batman. So the League is actually on the supply side of white collar crime...
- In The Simpsons episode "Much Apu About Nothing", an isolated bear attack leads the Mayor to fund a massive Bear Patrol scheme. Homer claims the lack of bears proves the Bear Patrol works, at which point Lisa points out that you might as well say that a rock keeps tigers away, since she's holding the rock, and she can't see any tigers. Homer's response? "Lisa, I want to buy your rock."
- Sesame Street had a Bert & Ernie sketch where Ernie held a banana in his ear, claiming it kept away alligators. Bert: "But there aren't any alligators on Sesame Street!" Ernie: "I know, it's working!"
- This has also been used to argue that listening to country music causes higher suicide rates, since places with a higher percentage of country music listening tend to also have a higher percentage of suicide.
- In an episode of Numb3rs, Charlie tells Don about the ice cream-rape correlation. As the sales of ice cream goes up, so do the number of rapes. The key is both take place during summer.
- This fallacy often comes up in discussions of videogame-related violence; the claim is that violent video games cause or encourage violent behavior in real life. This claim typically ignores other possible sources of correlation, such as that violence-prone people tend to enjoy violent games, or that some violent people prefer non-social activities that include games... or even that video games are simply becoming ubiquitous enough that almost every child plays them, so naturally the violent ones did too.
- The West Wing had an episode named after the Latin name for this fallacy, Post Hoc, Ergo Propter Hoc.
- Another prominent example often used in statistics classes: The declining number of storks is responsible for the declining birth rate. It should be noted that the stork population and the birth rate of humans are usually both being affected by some third factor.
- A particularly absurd (joke) example: the pretty-much-undefinable Column 8 in the Sydney Morning Herald once featured a letter correlating the difficulty of the newspaper's Sudoku with the price of petrol.
- Four terms fallacy: Using a standard 3-step proof-of-concept to prove your theory, but including one unconnected tenet which breaks the line of reasoning. Results from equivocation. It's better explained by example:
Nothing is better than eternal happiness.
A cheeseburger is better than nothing.
Therefore a cheeseburger is better than eternal happiness.
- This uses two different meanings of the word "nothing": the first line uses nothing to mean "there exists no such thing", while the second line uses nothing as in "an absence of food".
- An episode of Yes Minister called this fallacy "The Politician's Syllogism", specifically the form: "Something must be done. This is something. Therefore we must do this." The two different meanings of something: "A solution to this problem" and "A thing" are mixed and said to be the same.
- The Stephen Sondheim musical Anyone Can Whistle explains in "simple" terms what's wrong with leftists:
The opposite of left is right,
The opposite of right is wrong,
So anyone who's Left is wrong — right?
- This fallacy, combined with Reification, is the reason that one of the classic "paradoxes" is not really a paradox at all, namely, "If God can do anything, can he make a stone so big he can't lift it?" The term used twice is the idea of "can do anything". In the first sense it is abstract, referring to a lack of limitations; in the second sense it is referring to the limitations of physical strength and the laws of physics.
- God can't make a rock too heavy for him to lift, for the same reason that he can't make a square circle or a married bachelor. If something exists, He can affect it.
- This Troper always figured that the problem was semantic rather than realistic, and that, if necessary, God could, being omnipotent, alter reality in such a way as to do both at once. However, it would be far easier for Him to simply alter language so that the paradox no longer exists.
- Averted in Runaways - 'Could God make a sandwich so big He couldn't eat it?' 'Yes, and then He would eat it anyway.'
- Reification (no, not that kind): Sometimes related to the four terms fallacy, this is treating a abstract idea as a physical object. For example: "eating ice cream makes you happy. Therefore, eating more ice cream makes you more happy". This assumes that happiness is an idea that can be measured and which is a physical property of ice cream — in fact happiness is an unmeasurable emotional response to ice cream, and would probably tail off at around the point that you started to get really sick and/or fat.
- Ad hominem fallacy: Discarding an argument based on the character of the person presenting it, rather than the content of the argument itself. For example:
Bob thinks we shouldn't buy a pool, because it would be too expensive to maintain.
Why should we listen to someone who kicks puppies?
Therefore, we should buy a pool.
- This even applies when the ad hominem attack itself is related to the argument. Even if the supposition comes from a source that is known for fallibility, that does not logically make it untrue.
Bob thinks we shouldn't buy a pool, because it would be too expensive to maintain.
Bob once went bankrupt.
Why should we listen to economic advice from someone who went bankrupt?
Therefore, we should buy a pool.
- In fact, in some cases that fallibility may be a good reason to take advice from that person. I might well want to listen to economic advice from someone who went bankrupt. Maybe he went bankrupt because of the expense of maintaining a pool. Similarly, an admonition not to smoke would have more resonance coming from a smoker than from someone who never tried it themselves.
- Most people can recognize such a simplistic ad hominem attack as humorous, but that didn't stop Direc Tv from flipping out at a spot by Time Warner asserting that "DirecTv hates puppies"
- "Poisoning the Well" is a variant of Ad Hominem where a person uses an Ad Hominem attack before the other person even speaks, in an attempt to get the audience to pre-emptively discredit what they are about to say.
- The movie Enemy of the State has the evil NSA officer order his minions to destroy Robert Clayton Dean's (Will Smith) reputation before Dean can go public with his proof of the officer's misconduct.
- A variant of Ad Hominem, Tu Quoque states that a person's argument is invalid because that person is biased.
Bob thinks marijuana should be legal.
But Bob smoked marijuana once.
Bob is biased.
Therefore, marijuana should remain illegal.
- More specifically, Tu Quoque (literally "you, too!") refers to the attempt to deny an accusation by asserting that the accuser also suffers from the same flaw or has held an opposing view in the past.
Bob: "Smoking is a highly addictive habit and causes health problems. You should not smoke."
Alice: "But you yourself smoke! Therefore your argument is invalid."
(The fact that Bob smokes does not mean he is wrong.)
Bob: "This bill will be expensive and will not work, therefore you should vote against it."
Alice: "You supported the bill last month, so obviously you're wrong."
(Bob changed his mind in the meantime.)
- In some cases, Tu Quoque is a valid argument, but only when it is being used to question the speaker's reliability. It does not inherently invalidate the statement.
- This is one of the reasons that the Nuremberg tribunal specifically forbade the defendants from bringing up Allied actions that could be considered war crimes (for instance, the bombing of Dresden).
- This is a favorite tactic of politicians who want to discredit an opponent; they usually call it "flip-flopping" or "waffling" and use it to imply that the opponent can't make up their mind.
- Reductio ad Hitlerum (also known as "Reductio Ad Nazium"): Hitler did it, therefore it's bad. Can be extended to other evil or unpopular people, such as Osama bin Laden. While persuasive, it's not always true, since while Hitler did a lot of evil things, he also was a massive advocate of animal rights (more so than Jewish, gay or Gypsy rights...), built motorways, painted pictures, hosted the Olympics, ate sugar and breathed oxygen. Related to Godwins Law and Hitler Ate Sugar.
- Classic example: "Y'know, Hitler was a vegetarian." And therefore vegetarians are as morally suspicious as a dude with a German accent in an Indiana Jones film.
- "Vegetarianism then: not all it's cracked up to be. In some extreme cases may cause genocide." — Bill Bailey
- Bonus points: Hitler ate meat.
- An anti-abortion Chick Tract claims abortion is wrong because Hitler killed Jewish babies, and therefore doctors who carry out abortions are as bad as Hitler.
- The film Expelled is basically 90 minutes of Reductio ad Nazium calling evolutionists Nazis.
- In general, saying that something is bad because a bad person did/believed/approved of it is the association fallacy.
- The association fallacy, especially in its reductio ad Hitlerum form, is closely related to the ad hominem fallacy. In both cases, the goal is to link an opinion to a discredited person. The difference is that in a normal ad hominem you have to work to discredit the person you're linking the idea with, even if it's just by adding a claim that itself isn't true. But since everybody but Those Wacky Nazis hates Hitler, he comes pre-discredited.
- No True Scotsman — Redefining the terms in your argument to change the end result. The classic example works by redefining the word "Scotsman" from "person from Scotland" to "person from Scotland who doesn't eat sugar with their porridge":
Alice: No Scotsman puts sugar on their porridge.
Bob: That's not true — my Scottish uncle Scotty McScotscot puts sugar on his porridge all the time!
Alice: But no true Scotsman puts sugar on their porridge!
- The game Metal Wolf Chaos features propaganda news reports that define a true American as "anyone who supports the idea of having the families and friends of terrorist sympathisers murdered in the streets" rather than "anyone who is a citizen or long-standing resident of America". Unfortunately, only slightly less extreme examples are common in real life.
- Excessive use of this in the 2008 Presidential campaign led to The Daily Show (fake news for fake Americans) producing a handy test: 'Are You A Real American?'
- See also instances of Fan Dumb redefining "a true fan" from "someone who likes this work" to "someone who agrees with me."
- Even better are the ones who redefine true fans as "someone who hates this work now, but loved it when it was new".
- Many questions fallacy — phrasing your question in such a way that some answers are impossible. The classic example is "have you stopped beating your wife?" — whether you answer yes or no, you automatically admit to having beaten your wife at some point.
- One episode of The Simpsons has the family being accused of being unpatriotic but, when given the chance to clarify, are asked loaded questions such as, "Which part of America do you hate the most?"
- This is an easy way to brand someone a traitor in Paranoia- simply ask "Are you a happy communist?" If they say no, they're saying they're not happy, which is treason. But if they say yes, then they're saying they're a communist, which is also treason.
- Just asking these questions is an example of a False Dichotomy in that you assume the answer can only be 'yes' or 'no', whereas a normal person would say "I've never beaten my wife, get away from my family."
- It's a common cross-examination trick to do this, because the attorney conditions the witness to respond "Yes" or "No" to everything and then *Bam!* traps them with this and forces them to give a detailed answer. The delay as the person scrambles to shift back and think of the correct answer is what makes them look "shifty." It's the reason for the objection "Assumes a fact not in evidence."
- Strawman: Beloved of Author Tracts the world over, this fallacy involves misrepresenting your opponent's views, or only attacking their weakest arguments, and then claiming that because you beat this "straw man", you beat their entire argument. See The War On Straw.
- One variant is sometimes known as a "Red Herring" argument. Whereas the Straw Man will extrapolate details into a second argument in order to apparently defeat the first, a Red Herring will establish a second argument to try to make everybody else involved forget all about the first one. It's named for an old method of training hound puppies to follow a scent trail, by using a a "red herring" (a type of smoked, dried fish with a distinct scent) to lay down a trail for them to practice on. Because this was the scent they were originally trained to follow, dragging a red herring across a real scent trail could draw an adult pack off on a false trail.
- Affirming the consequent — Claiming that because the result of something is true, the original statement must also be true. For example:
If a car is a Ferrari, it is fast.
My car is fast.
Therefore it is a Ferrari.
- Denying the antecedent — the opposite of the above, where you say that because the initial conditions did not happen, the result is impossible. Example:
If a person is wearing a hat, they have a head.
I am not wearing a hat.
Therefore I do not have a head.
- Sunk cost fallacy — When somebody's sacrificed/invested a great deal in a cause or project, they tend to become irrationally dedicated to it. This applies even when the costs invested can't be recovered. More of a cognitive bias than anything. Example:
If I spend seven dollars more on this contest, I can win the prize.
I can buy the prize elsewhere for five dollars.
I have already spent X dollars on the contest. Since I don't want the money to be wasted, I will continue.
- A particularly tragic example of this — with much higher stakes — can be found in The Order Of The Stick: Start of Darkness.
- Tends to afflict professional sports teams as well. Team A signs Johnny Stud Muffin to a 10-year, $200 million guaranteed contract. Turns out, Johnny's a bit of a malingerer and spends the first three years playing poorly for Team A. Many, many teams in this situation will continue to play Johnny, even after it's clear that he's a bad player, simply because they invested assloads of money in him. The reality is, Johnny's getting that $200 million no matter what, so the best move is to cut him and play the best players.
- Not to mention fake sports companies. Far too often a "talent" is given a generous amount of screen time not because they're skilled, but because they've been signed to fixed-term, guaranteed-money contracts and the company feels that they have to get some use out of them, even if they pull down the show with them.
- In psychology this is generally related to cognitive dissonance theory. Which is basically the idea that when people think of themselves one way, but act in another way they will try to rationalize it. Specifically people think they make good decisions, but when the decisions aren't paying off, they throw more effort after it to make the decisions good rather than admit they made a bad decision.
- It's also known on social psychology as a great way to inspire obedience or adherence to a group. Cults are known for using this: How about you read a flyer? Sure, that cost nothing. Hey, why don't you answer this quiz on how happy you are with your life? Well... You've already read the flyer, that's not much more effort. How about going to a session? This technique is called Foot In The Door, or The Camel's Nose.
- In business, this is known as throwing good money after bad.
- In poker, the term is "pot committed". The best poker players can overcome the fact that they've put half of their money into the pot to get away from a hand that has little chance of winning (rather than throwing the other half in and busting out).
- More serious in life or death matters. Dead troops are a sunk cost, but many nations across history have continued on losing military campaigns because their leadership could not face up to having wasted troops. As in gambling or business, the usual result is even more waste.
- This is often the reason people will spend lots of time on internet arguments, even after they're losing. Or as Scott Adams put it, "Nothing makes [someone] argue harder than being proven wrong."
- Retrospective determinism — Assuming that because something happened it was therefore bound to happen. Often brought up as justification for Hitlers Time Travel Exemption Act by saying that World War II was inevitable.
- Extremely common for people who should know better, "If I (we) don't do/make/use it, someone else will". Most commonly used to justify a nation developing inhumane or destabilizing weapons. Also used by fans of fantasy fiction to claim that gunpowder is an inevitable invention when the idea of mixing up sulfur, charcoal, and saltpeter (made from urine) in the proper proportions is anything but inevitable.
- Error of composition — claiming that because a statement is true of the parts, it must be true of the whole. Example:
Everything is made of atoms.
Atoms are invisible to the naked eye.
Therefore everything is invisible to the naked eye.
- Wild Wild West. Everyone liked Will Smith and Barry Sonnenfield in Men In Black, so any movie made by this pair would be a hit, right?
- Cirque Du Soleil and Criss Angel are both popular, so it was believed that a collaboration between the company and the magician on a Las Vegas magic show was money in the bank; instead, Criss Angel — Believe is shaping up to be an embarrassing flop.
- Also known as the "Steak Ice Cream fallacy". Steak is good; Ice Cream is good. So steak-flavored ice cream must be great, right?
- Comedian Dave Attell used this exact example in one of his stand-up routines.
Two smells together just reek. Even your most favorite smells.
Like cotton candy, I love it! And scotch whiskey, yum-a-dumb-dumb
But cotton candy and scotch, that's a weird funk, it's like:
"Oh MAN! Did someone just f*** a clown in here?
- Error of division — generalizing from a whole to the parts. Example:
This ensemble show is extremely popular
Therefore, any show starring any member of the ensemble should be popular.
- The supposed Seinfeld curse is a classic example of this fallacy.
- Trail of the Pink Panther, Curse of the Pink Panther, Son of the Pink Panther: everyone likes a Pink Panther movie regardless of whether Inspector Clouseau (as played by Peter Sellers) is actually in it, right?
- Star Wars: The Clone Wars: a Clone Wars movie? The Warsies will love it, even though it is not directed by Genndy Tartakovsky or George Lucas and it's CGI.
- As of early 2009, Marvel seems to think Iron Man 2 will be just as good without Terrence Howard. Or Samuel L Jackson. Or potentially Jon Favreau.
- As of mid 2009, Terrence Howard's not in it, but Jackson and Favreau are.
- "Hey, Myth Busters is popular, and it has explosions in just about every episode! Let's make a show centered around Stuff Blowing Up!"
- The Cab Driver's fallacy: Similar to the sunk-costs fallacy; having a particular goal in mind and refusing to give up on it, however impossible it seems, while also ignoring the possibility of doing even better. Named from the tendency of taxi drivers to have a specific amount they'll try and earn each day. On slow days they will keep going to reach the target, while on good days they will quit early as soon as the target is reached. They would do much better when they go home early on slow days and keep going past their target if it's busy.
- Perfect Solution Fallacy: Arguing that a plan is no good because it won't completely solve the problem, even if it does make an improvement. For example, "Why bother with seatbelts? Some people will still die in car crashes."
- This is popular when answering a technical question on the internet: "There is no solution to your problem which I can guarantee to work in 100% of all cases. So I'm not going to bother telling you what will work in 99% of all cases."
- This is extremely popular with anti-vaccinationists. Their reasoning: a particular measles vaccine only protects 95% of the time, so they'd rather take their chances with a potentially fatal disease. Oh, how I wish I were making this up. This reasoning ignores that, due to herd immunity, 95% of the time is more than enough.
- This has even happened with the U.S. Army. In a series of tests to find a replacement for the M-16 assault rifle, all of the competitors were disqualified for not producing a guaranteed first-round hit.
- Also very popular among people who oppose condom distribution. Since condoms don't prevent pregnancy 100% of the time, and since there are certain ST Ds that a condom is ineffective against, it is better to simply take condoms off the table entirely than let people know they are effective most of the time for preventing pregnancy and STD transmission.
- Undistributed Middle — This fallacy occurs when the middle term of a standard three-step syllogism is not distributed in either premise. The picture at the top of this page is a case of undistributed middle. Using that image, "black and white" is the middle term; it is undistributed because neither premise refers to all things that are "black and white". Newspapers are black and white as well, and they are neither penguins nor old TV shows. "Things that are black and white" is the superset, and it contains many subsets that do not overlap at all. In casual use, undistributed middle can be hard to spot:
Conservatives always want to raise taxes.
Alice says that she's a Liberal, but she also says that the sales tax needs to be raised.
She's lying about being a Liberal; she's really a Conservative.
- The point is not how "Liberal" and "Conservative" are defined, it's that at no point is it established that only Conservatives can want to raise taxes.
- Inappropriate generalization, also known as proof by example(s): Taking one or more non-exhaustive examples from a group that have a property, and making a generalization that everything in that group has that property.
3 is a prime number, and it is odd.
5 is a prime number, and it is odd.
7 is a prime number, and it is odd.
Therefore, all prime numbers are odd.
- Note that it would be logical to prove that "at least three prime numbers are odd" by these three examples; it simply cannot be generalized to all prime numbers.
- Incidentally, all prime numbers are odd - except for 2, that is.
- Also note that the generalization can be made if the list of examples is exhaustive, in which case it is known as "proof by exhaustion" or "proof by cases", and is not a fallacy anymore:
The sum of the angles in any acute triangle add up to 180°.
The sum of the angles in any right triangle add up to 180°.
The sum of the angles in any obtuse triangle add up to 180°.
Since all triangles can be classified as one of acute, right, or obtuse, the sum of the angles in any triangle add up to 180°.
- Proof by obfuscation: Making your argument as confusing as possible in hopes that people can't find the flaws in your logic, then claiming you're right since nobody refutes you.
- The converse of that is to ignore or discredit an opinion just because it is confusing or poorly communicated. Just because the poster committed Aggravated Assault on their spellchecker is not proof that their points are incorrect. In the Internet this is often shortened to "TL,DR" (Too Long, Didn't Read).
- Argumentum ad nauseam, also known as proof by assertion: Repeating a statement until nobody cares to respond anymore, then claiming you're right since nobody contradicts you.
- The slippery slope fallacy is based on the idea that an object on the edge of a slope will slide all the way to the bottom if given even a small nudge. On a similar note, a small step taken in one direction will eventually lead to some drastic consequences, wouldn't they? This "argument" usually ignores the individual connections between events in favour of simply assuming one leads to another. However, it is not a fallacy if one does establish the chain of logical implications (or quantifying the relevant probabilities).
- Used frequently by politicians, naturally. Especially shows up around election time where voting for an opponent will usually be portrayed as resulting in a dystopia of some sort, usually authoritarian in nature, but is also used to argue against such changes as universal health care in favour of Status Quo Is God. Tropers Law is a form of the slippery slope fallacy used on this very wiki.
- The slippery slope fallacy is often combined with the strawman: Poster A explains why we should legalize Marijuana. Poster B claims that legalizing Marijuana will require us to legalize Heroin, and then post reasons why legalizing Heroin is a bad idea. If Poster B can show a proper logical chain, then this is an acceptable refutation, but rarely is that possible.
- If you give a mouse a cookie...
- One iaijustu (a Japanese sword style) master wrote that students should never practice cutting objects with their swords. The reasoning was that tatami mats aren't realistic enough, so we should cut chickens. Chickens aren't realistic enough so we should cut human cadavers. Cadavers aren't realistic enough so we will end up kidnapping people and chopping off their limbs to perfect our sword stroke.
A special subset of fallacies are appeals: claims that a position is right made by making an emotional argument without referring to your reasoning.
- Appeal To Nature: Claiming that something is good, or better than another thing, because it is natural, regardless of whether or not this is actually an advantage — after all, snake venom is natural, but that doesn't make it good. For examples, see All Natural Snake Oil.
- "Drink up, Socrates, it's all natural."
- In Troll 2, an evil witch is able to convince someone to drink a steaming green broth that has just turned someone else into green goo because "it is made from vegetable extracts".
- And let's not forget a similar scenario in the first episode of The Sarah Jane Adventures, where aliens convince millions of people to drink a new energy soda that contains alien parasites called "Bane" simply by claiming that Bane is "organic" (and by extension "healthy").
- And in the Discworld novel Carpe Jugulum, King Verence is talked into drinking a potion after being told "It's got herbs in", on the assumption it must be healthy. He spends most of the remainder of the book foaming at the mouth and randomly attacking inanimate objects. This, however, turns out to be useful.
- Also, scumble is made from apples. Well, mostly apples.
- A famous example from mathematics is Giovanni Saccheri's attempt to prove the parallel postulate. In his book, Euclid Freed of Every Flaw, Saccheri assumed the postulate was false and tried to derive a contradiction. Instead, he derived results that got stranger and stranger, finally concluding that they were "repugnant to the nature of straight lines". Saccheri didn't know it, but he was developing what we now call hyperbolic geometry — a fruitful field of study that just doesn't model the real world as well as Euclidean geometry does.
- The Eureka episode where everyone was becoming dumber, there was the supposedly also-a-genius farmer who didn't think the additives she were using were bad, since they were organic...In a town of super-geniuses, granted lacking in common sense sometimes, this seemed rather glaring in its stupidity
- Parodied in a Fry and Laurie sketch where a doctor is offering his patient cigarettes as a cure. "They're herbal are they?" asks the patient. "Yes, a naturally occuring called tobacco I believe"
- Appeal To Inherent Nature: If something is naturally predisposed to a certain act or state, it must be acceptable. Snakes bite, bears maul, poisons kill, babies scream and shit themselves, sociopaths torture and Nazis commit genocide; but those are their natures so we should not be annoyed.
- This one is Older Than Dirt. In the form of The Tale of the Scorpion and the Turtle, it dates back to an ancient Sanskrit collection of folklore that was first translated into English in 1570. "I'm a scorpion. It's my nature to sting."
- Real Life: Often used by people who want to excuse their own bad behavior rather than admit that maybe they crossed a line somewhere. "It's just the way I am." Not a 100% fallacious argument in that it's got some basis in fact when taken on the level of a single person, but fallacious enough that it usually comes off as lame and immature when people use it.
- A common example is Asperger's Syndrome-many people on the internet claim to have Asperger's (regardless of the medical community's opinion on the matter), in order to excuse any unacceptable behavior on their part without having to actually give up said behavior.
- Conversely this Troper, who actually has Asperger's Syndrome (and has turned it into his day job) is annoyed that 'claiming' to have an Autism-related disorder (or 'explaining' as it's called when it's actually true) is instantly seen as making excuses for behaviour that cannot actually be changed.
- This troper does also have Asperger's, was diagnosed at 12 (with a backstory that's good enough to fill a week in a Soap Opera), and does say that "I'm hardwired to act like this, but that doesn't mean I'm trying to change."
- When John Crichton, in Farscape, comes off to Aeryn as being unnaturally sex-obsessed, he says, "I'm a guy!"
- This is also a trope in certain religious/spiritual teachings, where it is assumed that value is subjective and not inherent to the thing in question.
- Appeal To Novelty: Arguing that one thing is automatically better than another because it is newer. See New And Improved.
- British Television Quiz QI is extremely guilty of this trope. The entire premise of the show is turning "popular" knowledge on it's head or proving old preconceptions wrong. As a result, lots of people believe the alternative, not for the inherent value of the statement, but because it's different.
- Appeal To Tradition: The opposite of appeal to novelty, where the older position is right. See They Changed It Now It Sucks.
- The short story "The Lottery" uses this.
- Illustrated in The Simpsons episode "Wacking Day", where snakes are herded to the town square and beaten to death with clubs. Lisa and Barry White are the only characters who are initially disgusted with the idea.
- In a similar vein, Weird Al's song Weasel Stomping Day is about a fictional holiday where people spread mayonnaise on their lawns, put on viking helmets and hiking boots in order to crush weasels to death. Complete with tongue-in-cheek lyrics such as "It's tradition that makes it okay" in order to mock the idea that an abhorrent act is acceptable if it is 'traditional'.
- Appeal To Authority: I'm right because this expert says the same thing. This one can be tricky, because citing experts isn't always fallacious. The determining factor is whether or not the person being cited is an expert on the subject being argued. Citing Albert Einstein on a question of Relativity is not fallacious. Citing him on a question of marine biology is.
- In Left Behind, the entire world believes a Technobabble nuclear physics explanation of the Rapture because a botanist and the president of Romania (note: not a nuclear scientist) say it's so. Later on in the book, the pseudoreligious explanation of the Rapture is accepted because it's espoused by an airline pilot. Because moderately distinguished airline pilots are noted for their theological expertise.
- In The Simpsons episode "The Monkey Suit", creationists seeking to ban the teaching of evolution succeed by getting a scientist to testify in court that evolution is a myth — a scientist with a degree in "Truthology" from "Christian Tech".
- Likewise, in one episode of Dinosaurs, in a trial for the heretical view that the earth is round, the "expert" who testifies that the world is flat's stated qualifications are that he is wearing a white lab coat and his "proof" that the world is flat is the existence of a flat-earth "globe". If a man in a white lab coat has a flat-earth globe, he can't possibly be wrong.
- Similarly, a combination of this and Appeal To Popularity (below) is used whenever people talk about however many scientists oppose or support the theory of climate change. What very few claims of this type state is how many of said scientists are climatologists, and even then, it doesn't state how many have actually done any accurate work studying climate change. Furthermore, it doesn't take into account the problem that climatologists can be well studied, have done a host of research, and still be wrong. Science is not decided by how many people agree, but by the one person who is right.
- Appeal To Wealth: Claiming that the position is correct because the rich or famous support it. This is the basis behind Celebrity Endorsements, especially when the celebrity's area of expertise is not relevant to the issue. See Screw The Rules I Have Money.
- Today people take advice about all sorts of things from showbiz celebrities.
- Lampshaded all to hell and back by a Sprite commercial that had NBA player Grant Hill doing the standard "Sprite is what I drink when my thirst really needs quenching" shtick while pictures of him holding fistfuls of cash appeared in the corner, with accompanying cash register sounds. The final screen said, "Drink Sprite because you like it. Not because an athlete says he does." This was used to wind down the "Grant Hill Drinks Sprite" ad campaign and kickoff the "Image is Nothing. Thirst Is Everything. Obey Your Thirst." campaign
- Appeal To Popularity: Many people believe it, therefore it must be right. See Quality By Popular Vote. This fallacy can be completely inverted while remaining the same, if the argument made is that "No one likes it, therefore it must be wrong."
- Basically, even if they are right in that particular instance, fifty-million Elvis fans can, in fact, be wrong.
- As can two hundred lemmings.
- Another prime example, as well as an Appeal to Authority. If everyone, including random authorities say lemmings commit mass suicide.... The truth: Stoats.
- The 'Appeal to Popularity'' fallacy is known as "Eat Shit! Millions of flies can't be wrong".
- Appeal To Consequences: The truth or falsity of a statement is decided by the positive or negative consequences of it.
If global warming is occurring and is caused by humans, then we are obligated to do something to stop or slow it.
The most effective way to do so is for businesses to cut down on carbon emissions.
The short term costs of cutting carbon emissions would be economically devastating.
Q.E.D: Global Warming is either not occurring, not caused by humans, or both
- Or, conversely,
If global warming is occurring and is caused by humans, then we are obligated to do something to stop or slow it.
The most effective way to do so is for businesses to cut down on carbon emissions.
The long-term economic benefits of stopping global warming will be enormous.
Q.E.D.: Global warming is both occurring ''and' caused by humans.
- Ain't it fun when you can use the same fallacy and essentially the same argument and prove diametrically-opposite conclusions?
- A related attempt to prove the existence of God is Anselm's Argument. To wit: Man can think some thoughts and imagine some ideas which are greater than others. An idea which is conceived of and which exists is better than one which is only imagined. There must exist some idea which is greater than all others. Such a thing would be God. Therefore God exists. This can be said to be an appeal to consequences because it assumes the most desirable possibility to be the real one, a bit like the preceding example about global warming. It also uses "greatness" in a rather shady way, leaves out the possibility that a fictional idea can be so much greater than all others that it doesn't need the added bonus of being real, and assumes that existence comes from the idea of a thing and not the experience of it, But that's beside the point.
- Can a fanfiction author write a Mary Sue who's so perfect that she even has the quality of existence in the real world?
- Only if God writes fanfic.
- That it is not possible to care about big and small problems simultaneously.
- That venting a minor complaint is sufficient proof that the major problem is considered unimportant.
- That if the person irritated over the minor problem did help the big problems, he would then not mind at all that his car broke down or whatever the frustration was.
Incidentally, I've never seen anyone who actually has charity work under their belt use disadvantaged people as leverage in arguments.
- This (specifically the starving African children) has become a fairly popular T-Shirt. It personifies Africa as saying "And you think you have problems..."
- Appeal to pity: (argumentum ad misericordiam): Attempting to make someone feel sorry for either the arguer or the subject of the argument, in order to convince them to accept the argument regardless of its validity.
Of course, before you get too carried away with these fallacies, there's one more you should remember:
- The fallacy fallacy: Claiming that a position must be false because the argument used to get to that position used a fallacy. It may sound logical, but just see an example:
To read TV Tropes, you must be on the Internet.
You are on the Internet, therefore you must be reading TV Tropes.
But wait, I just used the "Affirming the consequent" fallacy!
Therefore my argument was wrong, and therefore you're not reading TV Tropes at all!
- Lore has a nice video on the subject.
- Common in internet debates when one person knows logical fallacies but no one else does. This troper cannot count the times he's seen a Strawman argument for a claim of False Dichotomy when either alternatives were addressed originally or there otherwise really are only two options. Also claiming Appeal to Authority when someone uses a source for facts. Because when someone cites a source to establishes facts then argues from those facts there argument is not 'because X says so.'
- And don't forget the opposite of that, the "garbage in, garbage out" principle. If one of your premises is wrong, then the argument can be logically valid and still have a false conclusion.
The moon is made of cheese.
Cheese is edible.
Therefore, the moon is edible.
- You can also guess the conclusion, but use a faulty premise, and then if the conclusion is right, pretend your guess was perfectly logical. The argument is still faulty.
"The sky is blue because of fairies painting it."
The sky is blue, but because of the oxygen reacting to sunlight.
"What else floats in water?"
"A duck."
"If she weighs the same as a duck...then she's made of wood..."
"And therefore...?"
That systems wins, but because of Y and Z.
"I knew it would win!"
- And, to muddy the waters even more, your premises may be wrong, and your argument may be illogical, but you might reach a true conclusion anyway.
A human is a reptile.
All (known) reptiles live on Earth.
Therefore, all humans live on Earth.
The moon is made out of green cheese.
Green cheese is delicious.
Hitler was the political leader of Germany from 1933 to 1945.
Therefore, the more massive something is, the stronger its gravity.
Your Head A Splode now.
And all of that is why logicians do not use the words "sound", "valid" and "true" interchangeably. The chain of reasoning itself can be sound or unsound, valid or invalid, but the argument as a whole is not "true" or "false". The premises and conclusion can be true or false, but they are not called "sound" or "valid".
- "True" refers to the factual accuracy of the premises or the conclusion. It's exactly what it sounds like but it does not address the validity of the argument. (A fallacious argument can give a true conclusion.)
All animals are dogs. (false premise)
Formal logic isn't as complicated as it seems. (true premise)
Therefore, all dogs are animals. (true conclusion; no logical argument at all)
- "Valid" refers to the chain of reasoning, the logic part of the argument. It does not address the truth of either the premises or the conclusion. The logic must be correct, though. (Invalid logic results in a fallacy.)
All animals are dogs. (false premise)
All dogs are terriers. (false premise)
Therefore, all animals are terriers. (false conclusion; valid logic)
- "Sound" refers to the argument as a whole. The premises must be "true", the conclusion must be "true", and the logic must be "valid". (Using a fallacy results in an unsound argument.)
All terriers are dogs.
All dogs are animals.
Therefore, all terriers are animals.
The perfect argument, then, is true, valid, and sound. In other words the argument must be based on accurate information and not use any fallacies.
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