The problem is that logic requires writers to think pretty hard about what they write, and not all writers have time or inclination to do so. So they take shortcuts, creating fallacies which at best can lead to plot holes or, at worst, undermine the entire story.
Fallacies are common errors in logic. By strict standards, fallacies don't address the truth of the premises or syllogism; they only address the validity of the logic, and as the Sound/Valid/True rule demonstrates, "truth" and "validity" are not the same thing when speaking of formal logic. There is a reason there are Critical Thinking classes.
Where deductive logic is valid, the conclusion must be true if the premises are true. "If it rains, then the sidewalk will be wet" is valid, so if you know that it rained, you know that the sidewalk will be wet. If you simply reverse the terms and say "if the sidewalk is wet, then it rained", this would not be valid; likewise, negating the terms, yielding "if it did not rain, then the sidewalk is not wet", is also invalid. To correct this, you need to construct a "contra-positive," where you reverse the terms as well as negating them to get "if the sidewalk is not wet, then it did not rain".
However, inductive logicnote involves reasonable inferences of what might be true, but not necessarily. A sidewalk could be wet due to a passing street sweeping vehicle or neighbours carelessly watering their lawns. Seeing a wet sidewalk and concluding that there was rain is fallacious not deductively valid but it is not necessarily false, nor is it necessarily an unreasonable inference to make.
Logical fallacies are faulty deductive reasoning. This doesn't mean that they aren't effective at persuading. Many of them are extremely effective tools of persuasion. The key is that there are two primary routes of persuasion: the central (logical) route and the peripheral (emotional) route. To persuade someone using the central route, you need logic; a logical fallacy will make your argument fall flat on its face. To persuade someone using the peripheral route, you don't need logic; you simply need to play on their emotions. Some people are impassive to emotional appeals, and so you must use logic to persuade them; others are confused by logic, and so must be persuaded through emotion.
However, one must keep in mind that depending on the surrounding circumstances a deductively fallacious argument may still, nonetheless, be a reasonable and (inductively) logical argument that has decent prospects of being true despite the deductive logic being invalid. A classic example is if someone were to examine a million swans and note that all of them were white. It would be a (deductively) logical fallacy to conclude that "all swans are white". You could not make that conclusion unless you know that you had examined all swans in the universe. That doesn't make it illogical, however. If no one had ever seen a black swan, it might be rather sensible. Plus, this whole type of analysis is complicated when you talk about statistical trends. For these kinds of special cases, see the Fallacy Fallacy below.
For examples of characters falling into these fallacies (intentionally on the writer's part), see the main Logical Fallacies index. This is not an exhaustive list, and there are more fallacies in that index.
Users of ad hoc claims generally believe the excuses and rationalisations serve to shore up the original hypothesis, but in fact each additional speculative term weakens it. This is both due to the speculations being based simply on the faith that there might be an explanation, and because each additional term makes the hypothesis weaker according to the principle of Occam's Razor.
"Possibly," "probably," "maybe," "might" and "could" are all good markers of ad hoc claims.
It's a very common sight in justifying edits aimed at any supposedly negative trope, particularly if that edit calls upon things that might have happened to cause the item described. For example:
Here the second poster is not presenting evidence: rather, they are explaining what the evidence they do not have ought to look like.
It's a fallacy because at no point is it shown that A is the only possible cause of B; therefore, even if B is true, A can still be false. For example:
I clocked my car at 121 miles per hour.
Therefore, my car is a Ferrari.
Anecdotal Evidence is extremely prone to Confirmation Bias; when it doesn't fit one's viewpoint, it can be very easily dismissed as this fallacy. If it does fit one's viewpoint, it's a perfect example of that viewpoint applying to real people in the real world.
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.
Therefore, climate change is either not occurring, not caused by humans, or both.
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.
Therefore, climate change 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?
For contrast, the following is not Appeal To Consequences:
CO2 causes climate change regardless of source.
Even minor alterations to the Earth's climate would be catastrophic for humanity.
Q.E.D.: If humans wish to destroy themselves, humans should maintain or increase their current carbon emissions.
Instead, this is a contingent statement based on absolute facts that forms a chain of cause and effect.
The slightly more subtle form of Appeal to Force, Appeal to Fear isn't a direct threat, but nevertheless is based on the idea that something terrible will happen unless you agree with a given position. The difference can be summarized like this:
This is a fallacy because whether an outcome is frightening has no relevance to whether the initial statement is true or not. Social order may collapse if you disagree that 2 + 2 = 5 (as in 1984), but that does not mean that 2 + 2 = 5. A type of Appeal to Consequences, where someone is supposed to be afraid of an outcome and therefore assume it to be true or false as a result. In marketing, this fallacy is known as FUD ("Fear, Uncertainty, and Doubt") and is applied to the use of vague criticisms of opposing products in order to try to persuade consumers to buy by brand.
- Argument from Ignorance
- Argument from Lack of Imagination
- Argument from Personal Incredulity
The claim that a statement is true simply because it has not been proven false, or that a statement is false simply because it has not been proven to be true. More exactly, that if a claim A is incorrect, a separate claim B is automatically correct: it is thus a type of false dilemma, and based on Shifting the Burden of Proof onto whichever side of the argument you want to lose.
The essence of the fallacy is that if the original argument cannot explain everything right now, it must be false: the person committing the fallacy discards the possibility of gathering more evidence. This makes it essentially a claim of personal omniscience; if the arguer cannot imagine a way for something to have happened, it is clearly impossible: it is thus closely related to the Perfect Solution Fallacy, where solution A is discarded due to failing to measure up to an idealized perfect solution B. In addition, it eliminates all other possible explanations in favor of a preferred one: in the second example, for instance, the idea the victim was, say, strangled is simply discarded in favor of the preferred conclusion, without any clear reason.
Famously refuted by Carl Sagan with the statement, "Absence of evidence is not evidence of absence."
This fallacy differs from reductio ad absurdum, a legitimate debating technique; there, it is demonstrated that an absurd conclusion naturally follows from the underlying logic of an opponent's argument, therefore showing the argument as invalid. However, an attempt at reductio ad absurdum that itself uses faulty reasoning can leave you with this.
Also, just because an argument uses ridicule does not mean it runs afoul of this. A person who delivers a withering, logically sound counterattack in a mocking, rude manner is being a jerk. If the argument is still sound, it stands regardless of how insulting the phrasing is. It only becomes a fallacy when the arguer fails to explain why what they are arguing against is stupid or ridiculous and just expects you to go with it.
A variation is argumentum ad lapidem ("appeal to the stone"), in which a statement is dismissed as absurd, but with no proof that it's absurd.
See also Argument of Contradictions, in which both sides repeat their side of the argument briefly, rapidly, and back-and-forth, or simply shout something in the form of "Is not!" "Is too!" in the hope of wearing down an opponent or simply not being willing to back down or provide actual logical reasons.
This is referred to as Fear of Loss in sales; a salesman will claim that he's only allowed to sign up a certain number of people to a fantastic deal and has already got most of his quota for today, so if the person he's speaking to doesn't act they stand to lose out.
There are also times this argument is valid, such as when there are what economists call network effects. In brief, if the value of a good or service changes based on the number of users, then pointing out the number of using it could be valid. For example, when telephones were adopted, their value increased with every new telephone added to the network. If business software is used by many companies, being ubiquitous is a selling point. If no one else uses an instant messenger, it's useless, but if everyone uses it, it's more valuable to the end user. If all of one's friends use a specific social networking site and you want to use social media, it makes sense to follow your friends. If a cell phone company allows unlimited calls between two members of their networks, the number of clients they have and their demographics are both legitimate concerns. If most counties and companies are using a particular shipping container, rail-road gauge, or standard of measure, there's good reasons to adopt the same standards.
- Petitio principii (Latin: "pursuit/attack of the source")
Also called "Circular Reasoning," begging the question is "proving" that something is true by taking your conclusion as one of your premises, usually done implicitly rather than explicitly. Few people are fooled by having your conclusion as your only premise, as in "Joe is mad at Jill, therefore Joe is mad at Jill." In rhetoric, such arguments are called tautologies, and they're essentially a pretty but meaningless way of saying the same thing twice. Therefore an argument which is begging the question often isn't obvious, even to the one making it. A premise may be substantially identical to or assume the truth of its conclusion, but be concealed by using different vocabulary, phrasing, sentence structure, or go unstated entirely.
Logic, meanwhile, has its own form of tautology: a statement or chain of statements which are sound, valid, and true under any condition.note Begging the question is what happens when you confuse the two.
Put broadly, this fallacy applies to any argument where one or more premises are at least as contentious as the conclusion itself, and for the same reasons, such as:
If an honest person says something, it must be true.
Therefore Alice is an honest person, because an honest person says so.
An example where the fallacy is more hidden might go something like this:
In this example, both the premise and conclusion are based on Marxist ideology. If one were to accept one, by definition one already accepts the other. In other words it is not an "argument" at all, but merely a statement that says, "I am a Marxist."
Note that begging the question in arguments can be perfectly valid, logically speaking. However, they are not considered convincing because they do not prove anything other than what was already assumed.
"Begging the question" is often used colloquially to mean "raising the question". (Example: "With the rise of online media, this begs the question: do public libraries have a future?") This usage is a common Berserk Button for academics aware of the original meaning. It doesn't help that the original phrase was first translated from Greek into Latin, and from Latin into English, resulting in the confusing phrase, "Begging the question," which is incomprehensible to English speakers (there being no begging nor question involved) unless one is already aware of its meaning.
The Other Wiki expresses Bulverism as:
- You claim that A is true.
- Because of B, you personally desire that A should be true.
- Therefore, A is false.
In short, it can be summarized as "You're only claiming X to be the case because you want X to be the case!". This is fallacious since whether or not someone wants something to be true because it would benefit them personally has no bearing on whether or not it actually is.
The term was coined by C. S. Lewis in an essay of the same name in which he describes the (fictional) origin of the fallacy: a boy named Ezekiel Bulver heard his parents arguing when his mother said "Oh, you say that because you are a man." at which point Bulver realized that "refutation is no necessary part of argument".
Lewis himself summed up the fallacy as "to assume without discussion that [your opponent] is wrong and then distract his attention from this (the only real issue) by busily explaining how he became so silly."
So far as cab drivers are concerned, this may be explained by risk-aversion. When it comes to something like income, most people are risk-averse - they would rather be guaranteed a steady flow of money rather than risk a large variance in the amount received (possibly negative) turn-by-turn, even if the latter would yield more money in the long run.
I am not wearing a hat.
Therefore I do not have a head.
Note that, by the contrapositive rule, these two fallacies are equivalent. For example, you could replace "If a person is wearing a hat, they have a head" by the logically identical statement "If a person has no head, they aren't wearing a hat" to turn the first example of denying the antecedent into an example of affirming the consequent.
Bill's rebuttal is an appeal to fallacy, because Ginger may very well be a cat; we just can't assume so from Tom's argument.
In other words, pointing out somebody's fallacy is not fallacious in itself (you're doing it right), but using this as "proof" that their claim is false is the Fallacy Fallacy. Somebody arguing their point badly doesn't automatically mean they are wrong. The best you can say is that they have not convincingly supported it. This also applies to the Fallacy Fallacy itself: Bill's argument is a fallacy, but it would be the same fallacy to conclude that Ginger is a cat because of that, since Tom's only "proof" is not a valid argument.
It should be noted that the burden of proof applies here: if the only reason to accept a claim is a fallacious argument, accepting the claim anyway is unreasonable. If our null hypothesis is that Ginger is not a cat, Tom has given us no reason to change this assumption. As above, it may well be that Ginger actually is a cat, but logic doesn't decide what's true, it decides what makes sense.
Another excellent example of how a false argument is combined with a true conclusion: in medicine, pressure around the brain can cause severe headaches. Ancient surgeons assumed that it must be demons in the patient's head causing the pain, and that exposing them to light would kill them or drive them out; therefore, they drilled holes in the patient's skull. The end result relieved the pressure and actually did cure the headaches, even though their reasoning was entirely faulty.
An argument using fallacious reasoning is consequentially capable of being true. In logic, "invalid" (fallacious argument) and "false" are not synonymous (See Sound/Valid/True for a more complete explanation of this. There are reasons why extensive Critical Thinking courses exist.) This is related to how logical argument is used as a tool rather than as a fact-in-itself, and that logical validity can sometimes be surpassed by an objective scientific fact.
It should be noted that there are some exceptions: namely, fallacies of distraction or relevance. A Strawman argument may still have a true conclusion, for example, but by definition it is an irrelevant conclusion since it does not address the opponent's real argument. Demonstrating the opposing argument is a strawman is therefore a valid rebuttal.
A type of generalisation fallacy.
Therefore, this ant can destroy that tree.
This assumes that "ethics" is a synonym for "non-self-interested."
This assumes that the role of the State must be an active one — i.e., the State must exist. (This applies whether one is arguing that Anarchism is not a valid political position, or that Anarchism is somehow "above" politics.)
This is seen in any case where a source is either highly disparaged or esteemed. Sources will commonly be accepted or dismissed out of hand without looking into the actual validity of their facts or arguments.
However, people who assume that such actions were the result of human nature that is present in all human beings, tend to forget about those other kinds of people who actively try to help people in need (or at least support those, but cannot do much about it). These characters would assume that such actions are reflective of the entire human race, making flimsy claims of many people who do help only do so out of Pride and publicity (while there are some who do that, there are also much more people who genuinely want to help) and that ideas of hatred, prejudice and self-destruction are inherent in all human beings. They all reject claims of Rousseau Was Right and the idea of a Blank Slate, replacing them with Humans Are Bastards (or the real monsters in certain cases). Sometimes, they would deny that they share those aspects with humanity, claiming that their suffering was of the actions of humanity (when it could be their own fault) or embrace that they're part of humanity and using that as an excuse for their actions.
More blatant examples include dismissing the victims of such atrocities as being just as bad as the perpetrators, including children as part of their perceived Human Nature and igniting a Family Feud between family members, just because they perceive them as bastards deep down, no matter how they treated them.
The other way around is the assumption of all of humanity being good deep down, no matter how cruel their actions may be. Some may say that such actions were only brought upon due to their upbringing. Whilst a person can be influenced by their upbringing, characters who believe humanity is inherently good from birth would not accept that there are people who are deep down cruel. They would try to reason with even the most negative aspects of humanity, preferring to appeal to whatever little or no aspect of goodwill they have over actively combating them. They would also not recognize that there are people who are completely beyond redemption.
The more lighthearted variant is when someone assumes that all humans share a similar opinion on something, or similar habits and the like, when it's most likely not true. Such as "everyone likes spicy foods" or "everyone likes a certain film" or "everyone thinks about sex".
This idea is rarely treated as a necessary worldwide view in fiction, but when it does happen, there is a high chance of Too Bleak, Stopped Caring or Tastes Like Diabetes and accusations of the Author expressing this view.
See also Tragic Bigot and Appeal to Inherent Nature. Compare Blank Slate, Humans Are Flawed. Contrast Humans Are Bastards, In Your Nature to Destroy Yourselves, Hobbes Was Right (for the cynical version) and Humans Are Good, Rousseau Was Right (for the idealistic version). Also contrast Humans Are Indexed, which list common human archetypes.
A variation is treating a thought experiment as a physically workable one; for example, imagining that one could use Schrödinger's box apparatus to actually cause quantum superposition of a cat.
Besides a word's definition, most words have a connotation that implies that its subject is either good or bad. For example, both the words "cabin" and "shack" mean basically the same thing, but one word has a positive connotation and the other has a negative connotation. Using a loaded term by itself isn't fallacious, but using loaded terms as a basis for an argument is. Using a loaded term to imply that the subject in question is bad when the point of your argument is that it's bad is also another form of Begging the Question.
Often, a non sequitur results from the writer believing that the statement results from an "obvious" argument that doesn't need to be explicitly stated.
For when this actually works as an argument, see Chewbacca Defense. When this is to such an extreme that attempts to consider it in any rational manner results in maddening frustration, it is Insane Troll Logic.
13 is odd, and it is a prime number.
97 is odd, and it is a prime number.
Therefore, all odd numbers are prime numbers.
Or in other words, this fallacy is about mistaking inductive reasoning for deductive reasoning. A common version is to assume that anything can be extended off to infinity, or that since having a little of something is good, having more must be better. It's a line of thinking commonly used by those talking about future technology.
As the name implies, this fallacy is a favorite of prosecutors in legal cases and sometimes in procedural shows like CSI — it can be quite tempting to argue, "How likely is it that this really happened the way the defendant said it did, if the odds of it happening that way are 1 in 10 million? Which is more believable — that he's lying or that something that improbable really happened?" It also lends itself well to Cassandra Truth plots.
An argument of this form often ignores that unusual cases are, well, unusual. We tend to notice unusual events more than common events, and the very fact that the issue is being argued over guarantees that it is likely an unusual event. For instance, if a practised hunter accidentally shoots his friend, one could argue that the odds of him making such a serious error is very small. But then, the alternative explanation is that the hunter purposefully shot his friend, which is also somewhat unlikely. In the end, the event itself can only be explained by one of several improbable explanations, and so the fact that they are improbable ceases to be relevant.
Bob: After I went out for a walk, I was bound to trip and break my knee.
Bob gives no real reason as to why this was the only possible result, or even why it was the most likely; it differs from False Cause in that he did break his knee as a result of going out for a walk. He might follow on by cautioning Alice to avoid going outside, lest she suffer the same fate. Often happens during arguments over Alternate History, as someone attempts to argue for the historical result being inevitable.
More seriously, people use this to comfort themselves after losing someone, saying "it was their time." Unless they really believe that each person's time of death is determined beforehand, they don't really mean it (especially as that would be very depressing).
This fallacy is somewhat of an inversion of the False Dichotomy, in which someone ignores any grey area and posits that only two contrasts exist. The Semantic Slippery Slope emphasizes any grey area and disregards clear differences. In short, saying the concept is too vague for any real decision to be made. The Semantic Slippery Slope Fallacy is also related to the regular Slippery Slope Fallacy insofar as committing the former will often cause the latter by inferring that one thing will inevitably cause the second thing, or that they're the same thing altogether.
This is a good demonstration of why the negative side doesn't bear the burden of proof; it is for all intents impossible to demonstrate something is absolutely incapable of happening, and it would be impossible to live one's life in light of all the things that might be true. It's far easier to demonstrate proof of the positive (if it exists). Put more simply, if someone has advanced no good reason to believe something is true, believing it is true anyway is unreasonable. This does not necessarily mean it is untrue (see the Fallacy Fallacy), but it does mean it is not logical to believe it is true.
Linguistic trickery can often be used to make a negative appear to be a positive (for example, claim that rejecting the existence of the invisible landmines is a positive claim that "I can explain everything in the universe right now"). It pays to be careful in evaluating which side the burden actually belongs on.
One popular form of shifting the burden of proof is to demand your opponent do their own research. This places the onus for proving the point you're trying to make onto them. This particularly applies if the research they're supposed to perform is defined extremely vaguely, such as take some classes, you can find dozens of examples or even use common sense.
This is fallacious because even if someone has certain expertise or is part of a specific group, they still have to provide evidence and cogent reasons for their position.
Another example could be formulated like this:
In this example, the principle of helping the police is applied to investigations of police officers but not to ones neighbors.
Also known as misleading vividness or the Volvo Fallacy, this is a close cousin to the Anecdotal Fallacy. The Spotlight Fallacy is making a generalization based on how much news coverage a subject gets. This is fallacious because the news media tends to focus heavily on events that are less common in real life. However, because the news covers them so extensively, it's an easy mistake to make.
It's said that "'Dog Bites Man' is not news; 'Man Bites Dog' is news." Using that example, this trope is when somebody assumes that men biting dogs is more common than the reverse, because it appears in the papers more often.
Zero-point field theories include conservation of mass / energy as an assumption. They would disprove themselves if they actually made this conclusion.
The notion of "proof" assumes the objective existence of something to prove in the first place. Additionally, if nothing existed objectively, there would be no reliable methods of proof, including quantum physics.
While most people will not be fooled by a blatant misrepresentation of their position, careful use of a strawman can make them defend a carefully undermined version of their position, allowing their opponent to apparently destroy them with a prepared rebuttal. However, it's more often used to get the audience on one's side than it is to confuse the opponent, especially when it's coupled with an Ad Hominem implying that the opponent is immoral for "holding" the strawmanned position.
The opposite is called the Steelman, where one argues against the best possible version of an opponent's position.
No Muslims are Christians.
Therefore Jews are Christians.
No reptiles are magenta.
Dogs are magenta.
No reptiles shoot lasers out of their eyes.
Dogs shoot lasers out of their eyes.
Alice says that she's a conservative, but she also says that the sales tax needs to be raised.
She's lying about being a conservative; she's really a liberal.
The point is not how "liberal" and "conservative" are defined; it's that at no point is it established that only liberals want to raise taxes. Put another way, saying "All liberals are people who want to raise taxes" is not the same as saying "All people who want to raise taxes are liberals."