Logical Fallacies
aka: You Fail Logic Forever

Logic. Every story needs some of it, unless you just want a series of unconnected images and no plot to speak of.

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 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 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 Fallacy Fallacy.

For examples of characters falling into these fallacies (intentionally on the writer's part), see Insane Troll Logic and Chewbacca Defense. Not to be confused with Logic Bomb.
  • Ad Hoc: Mistaking an argument for an explanation.
  • Ad Hominem: Attacking the arguer or the argument's presentation instead of the actual argument.
    • Appeal To Hypocrisy: Claiming an argument is invalid because the opponent fails to act consistently in accordance with its conclusion(s), or arguing that since the opponent previously held the opposite position, their current position is untrue or untenable. Very popular in politics.
  • 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 Force: Threatening anyone who disagrees with you, and therefore claiming what you say is true: "changing your mind by altering your face." Another species of the Appeal to Consequences.
    • Appeal to Fear: Saying bad things will happen to anyone who disagrees with you, and therefore what you say is true. Yet another species of the Appeal to Consequences.
  • 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 Ignorance: Claiming that something must be true simply because nobody has proved it false (or vice-versa).
  • Appeal to Inherent Nature: Claiming something otherwise unacceptable is acceptable because it is within the nature of the doer to do it.
  • Appeal To Morality: Claming anything that is morally desirable is true/natural, and anything that is immoral is false/unnatural.
  • 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 Possibility: Claiming that if something can't be shown to be completely impossible, it must be true. A type of False Dichotomy.
  • 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: Discarding an argument on the basis that it is unimportant because of a related thing that is perceived to be more important. A type of Red Herring.
  • Argument of Contradictions: An argument that consists of nothing more than a shouting match — each side loudly repeating their side in turn.
  • 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 explaining why.
  • Association Fallacy: Claiming "X is a Y. X is also a Z. Therefore, Y is a Z." Incorporates Guilt / Honor by Association, where it is asserted that relation to a good or bad thing means the associated thing is also good or bad.
    • Hitler Ate Sugar: Claiming something is bad because an evil person (like Hitler) liked it. A species of the Association Fallacy.
  • Bandwagon Fallacy: Accept or adopt something simply because the majorities have already done so, regardless of actual validity or desirability.
  • Begging the Question: Mistaking the argument for the evidence. "People who use X are in danger of Y, because X can Y."
  • Broken Window Fallacy: Thinking the costs for recovering from disaster are equal to the benefits.
  • Bulverism: Rather than proving a statement wrong, assuming that it is wrong and then explaining why your opponent holds it.
  • Cab Driver's Fallacy: Being so devoted to meeting a quota that one tries too hard when there is little reward to be gained or doesn't try hard enough when great rewards are available.
  • Chewbacca Defense: Using non-sequitur arguments to prove a point, relying on distracting and confusing the opposition.
  • Circular Reasoning: Any argument in which the conclusion is used as a premise: for instance, "A is true because A is correct."
  • Confirmation Bias (also known as cherry-picking): Presenting only data that supports your predetermined position and ignoring data that damages your position.
  • Converse Error: Concluding that a certain set of results can only come from one set of circumstances. "If A, then B. B, therefore A."
  • Correlation Implies Causation: Believing that any two variables that happen together after another represent a cause and effect pairing. "When X occurs, Y goes up. Therefore, X causes Y to go up."
  • Extended Analogy: A comparison between X and Y for purposes of demonstrating a specific point is taken as a statement that X and Y are analogous in additional ways.
  • Fallacy Fallacy: Because someone used a fallacy to argue a point, their premise must be incorrect.
  • Fallacy of Composition: The properties of the parts are applied to the whole. "A is made of B. B has property X, so A has property X."
  • Fallacy of Division: The properties of the whole are applied to the parts. "A is made of B. A has property X, so B has property X."
  • False Cause: Assuming that because one event came after another, that the first event must have caused the second.
  • False Balance: Also known as the "balance" fallacy, this is the belief that if two opposing positions exist, they must be treated as equally credible regardless of what the positions in question actually are.
  • 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 (False Syllogism): "God is love. Love is blind. Stevie Wonder is blind. Therefore, Stevie Wonder is God."
  • Frozen Abstraction: An argument implicitly assumes that a subset of a wider class is the wider class. "Anarchism cannot be a political ideology because it denies the state."
  • Gambler's Fallacy: Thinking that previous random events will have an effect on future random events. "Odds of winning are 1:20, I've played 19 times, I'm due for some good luck."
  • Genetic Fallacy: Dismissing or accepting something entirely on the basis of its origin.
  • Golden Mean Fallacy: Thinking that the "middle ground" between two points is the best option, even when it shouldn't apply.
  • Hard Work Fallacy ("If I can do it, so can you."): The argument that the desired outcome is purely the result of the effort put in by the individual, regardless of any other factors.
  • Historian's Fallacy: When one assumes that a decision-maker had the same information and perspective as those analysing their decision(s) with the benefit of hindsight.
  • Hypostatization: Treating an abstract idea as a physical object. "Eating ice cream feels good. Therefore, we should give ice cream to criminals, so they become good."
  • Incriminating Indifference: "You are not acting as emotional as we think you should be. Therefore, you are guilty/untrustworthy/hiding something."
  • Insane Troll Logic: A conclusion drawn on irrelevant or nonsensical postulates.
  • Irrelevant Thesis: Not refuting the opposing position at all, but acting as though you did.
  • Lets See You Do Better: Claiming that one must be able to perform something in order to be able to criticise it, regardless of their arguments. A type of ad hominem.
  • Loaded Words: Using words which appeal to emotions rather than to logic.
  • Many Questions Fallacy: A question is asked that assumes the answer to one or more additional questions, and a demand is made that it be answered without qualifiers. "Yes or no: have you stopped beating your wife?"
  • Moving the Goalposts: Continually changing requirements for a goal so that it is never achieved.
  • Nirvana / Perfect Solution Fallacy: Comparing actual things with unrealistic, idealized alternatives. "If we can't fix it perfectly, we shouldn't try at all."
  • Non Sequitur Fallacy: Coming to a conclusion which is not supported by the facts or even has no relationship to the facts.
  • No True Scotsman: Redefining a category to not include something that the speaker doesn't want it to include, even though it does in fact include that thing.
  • Original Position Fallacy: Claiming something is good on the assumption that one will gain benefits from it, ignoring the possibility that they may not.
  • Oven Logic: Assuming that any one condition can still produce a valid result if a second condition is altered 'proportionately', such as by baking something for half the time at double the temperature.
  • Overwhelming Exception: A generalization with so many exceptions that what remains is less than impressive, if useful at all.
  • Poe's Law: Satire mistaken for fact, used by someone who states it as fact.
  • Presentism: Present-day ideas and perspectives being anachronistically introduced into depictions or interpretations of the past.
  • Proof by Examples: Generalizing a category to match the properties of a non-exhaustive list of given examples. "3, 17, and 97 are prime numbers; all odd numbers are prime."
  • Prosecutor's Fallacy: Rejecting an explanation on the basis that it relies on exceptional circumstances in favor of an equally exceptional, but personally desired, explanation.
  • Red Herring: In logic, a fallacy of distraction where an irrelevant side-argument is introduced in an attempt to draw the opponent away from their main one. For example, Alice tells Bob it is immoral to cheat on his wife Claire because it is betraying her trust, and Bob replies, "what is morality, though?" intending to redirect a discussion of his affair into a discussion of abstract philosophy.
  • Retrospective Determinism: Assuming that because something happened it was inevitable.
  • 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 to a general rule 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.
  • Spurious Similarity: It is suggested that some relatively superficial resemblance is proof of a relationship.
  • 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.
  • Style Over Substance: Arguing the manner in which information is presented affects the truth of the information: "Bill was very polite in presenting his points and Bob said my wife was a bitch while he was presenting his, so Bill must be right." A type of ad hominem.
  • Subjectivist Fallacy ("That's just your opinion"): Claiming that subjectivity means all conclusions are equally valid, regardless of their underlying logic.
  • 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 though it produces no gains.
  • Suppressed Correlative: Redefining two mutually exclusive options presented by an opponent so that one encompasses the other: "you say this isn't art, but I define art as this, which means it is." A specific subtype of strawman fallacy, since it is based around rebutting an argument framed in different terms to those originally used and thus a point the opponent never made.
  • Survivorship Bias: Over-playing a small number of successes of a given example, while ignoring a large number of failures.
  • 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."

... The following are relevant argumentative concepts that are not fallacies:

  • Occam's Razor: The explanation that adds the least number of speculative assumptions while explaining all the evidence is most likely to be the correct one.
  • Hanlon's Razor: Don't assume malicious intent when stupidity could do.
  • Sound/Valid/True: "Truth" means factually accurate. "Valid" means logically constructed. "Sound" means both valid and true.

"A foolish consistency is the hobgoblin of little minds, adored by little statesmen and philosophers and divines."
Ralph Waldo Emerson

Alternative Title(s): Logical Fallacy, You Fail Logic Forever, Just World Fallacy