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*Producers notice a fairly small sign blending in, reading "Flim Springfield"*
—Radioactive Man Producers, on the topic of Springfield as a movie location, The Simpsons
The problem is 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, and 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 this page 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 (to correct this you need to construct a 'contrapositive' 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 logic 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 zealously and carelessly watering their lawns. Seeing a wet sidewalk and concluding that there was rain is fallacious - not deductively valid - but it is not necessarly 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 upon 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, none the less, 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 where 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.
- Ad Hoc: Mistaking an argument for an explanation.
- Ad Hominem: Attacking the arguer or the argument's presentation instead of the actual argument.
- Anecdotal Fallacy: Using a personal example as empirical evidence.
- Appeal to Authority: Assuming something is true because an authority said it to be so OR calling someone an expert (and therefore correct) when they are not an actual expert.
- Appeal to Consequences: Assuming something is correct/incorrect because of the positive/negative effects that will arise if it is implemented.
- Appeal to Fear: Saying bad things will happen to anyone who disagrees with you.
- Appeal to Flattery: Claiming that a certain conclusion reflects well on anyone who agrees with it, or poorly on anyone who does not.
- Appeal to Force: Threatening anyone who disagrees with you.
- Appeal to Ignorance: Claiming something is true/false because it has never been proven false/true.
- Appeal to Inherent Nature: Claiming something otherwise unacceptable is acceptable because it is within the nature of the doer to do it.
- Appeal to Nature: Claiming anything that appears naturally is good, and anything that appears unnaturally is bad.
- Appeal to Novelty: Claiming something is superior to something else because the first is newer.
- Appeal to Obscurity: Attributing an argument to someone the other party doesn't know and using the fact that they aren't known as evidence.
- Appeal to Pity: Claiming an argument is valid because either the arguer or an involved party deserves sympathy.
- Appeal to Popularity: Claiming something is true because many or most people believe it.
- Appeal to Ridicule: Claiming an argument is false by presenting it in an absurd fashion.
- Appeal to Tradition: Claiming something is superior to something else because the first is older.
- Appeal to Wealth: Claiming something is good because the rich or famous support it.
- Appeal to Worse Problems: Claiming an argument isn't valid because there are bigger problems than it.
- Argumentum Ad Nauseam: Repeating an argument over and over until no one wants to dispute it anymore, then claiming it to be correct.
- Argumentum Ad Lapidem: Dismissing an opposing argument as absurd without any sort of support.
- Association Fallacy: Claiming "X is a Y. X is also a Z. Therefore, Y is a Z." The page image is an example of this.
- Bandwagon Fallacy: Claiming that because everyone or a large number of people believe or support a thing, it must be true.
- Begging the Question
- Cab Driver's Fallacy
- Chewbacca Defense: Using non-sequitur arguments to prove a point, relying on distracting and confusing the opposition.
- Circular Reasoning
- Confirmation Bias
- Converse Error
- Extended Analogy
- Fallacy Fallacy
- Fallacy of Composition
- Fallacy of Division
- False Cause: Assuming that because one event came after another, that the first event must have caused the second.
- False Dichotomy (Either/Or Reasoning): Offering a choice between two extremes, usually one desired and one not, and ignoring the possibility of other options.
- Four Terms Fallacy
- Frozen Abstraction
- Gamblers Fallacy
- Genetic Fallacy
- Golden Mean Fallacy
- Hitler Ate Sugar: Claiming something is bad because an evil person (like Hitler) liked it.
- Irrelevant Thesis
- Loaded Words
- Many Questions Fallacy
- Moving the Goalposts
- Nirvana / Perfect Solution Fallacy: Comparing actual things with unrealistic, idealized alternatives.
- Non Sequitur Fallacy
- No True Scotsman
- Proof by Examples
- Prosecutor's Fallacy
- Retrospective Determinism
- Sharpshooter Fallacy: Claiming that a conclusion is inevitable after the specific results have already been witnessed: "Painting the target around the bullet hole."
- Shifting the Burden of Proof: Arguing that the burden of proof lies with the side it does not normally lie with: "guilty until proven innocent."
- Slippery Slope Fallacy: Claiming that an action will inevitably lead to another, very unacceptable action. "If X, then eventually Y."
- Special Pleading: Demanding an exception be made without justification or for a non-logical reason ("I can park in the handicapped spot because I'm a movie star!")
- Spotlight Fallacy: "I've been hearing a lot about event X in the news lately, so event X must happen a lot..." when an event only appears in the news because it's unusual.
- Stolen Concept: Making an argument that rests upon (and conveniently ignores) contradictory, intrinsically self-refuting concepts.
- Strawman Fallacy: Deliberately misrepresenting an opponent's argument by constructing it in such a way that it can be easily defeated.
- Sunk Cost Fallacy ("Throwing good money after bad"): Assuming that because one has already invested time or money into something, it is worth continuing to do that thing even if it produces no gains.
- Tautological Templar: Self-identifying as definitively good or right, then using it as a supposition for argument. "I'm a good guy so everything I do is good because I say so."
- Two Negative Premises: Identifying what something isn't doesn't identify what it is. "No dogs are reptiles. No reptiles are magenta. Therefore dogs are magenta."
- Undistributed Middle: When the middle term of a standard three-step syllogism is not distributed in either premise. "Penguins are black and white. Some old TV shows are black and white. Therefore some penguins are old TV shows."
... And not fallacies but relevant-
- Occam's Razor
- Hanlon's Razor: Don't assume malicious intent when stupidity could do.
- Sound, Valid, True