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Logical Fallacies

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Tropes about characters misusing logic or otherwise failing at it.

See also the Useful Notes page on logical fallacies, which covers fallacies that don't have their own pages.

Subtropes include:

  • Abilene Paradox: A group-think fallacy in which the individuals in a group don't want to hurt any of the others' feelings and end up doing something nobody wants because they all think they're going along with everyone else.
  • Ad Hominem: Attacking the arguer or the argument's presentation instead of the actual argument.
  • Appeal to Authority: Assuming something is true because an authority or expert said it to be so (in cases where other experts may disagree, or if neither you nor the authority / expert are unable or willing to elaborate further) OR calling someone an expert (and therefore correct) when they are not an actual expert.
  • Appeal to Consequences: (better known as "argument from adverse consequences") Assuming something is correct/incorrect because of the positive/negative effects that will arise if it is implemented.
  • Appeal to Familial Wisdom: A subtrope of Appeal to Authority where advice is lent extra weight by claiming it was passed down from one's parents.
  • 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, and therefore claiming what you say is true: "changing your mind by altering your face." A species of the Appeal to Consequences.
  • 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: Building an argument out of obscure acts that might be irrelevant and incorrect, and claiming it is valid because the other person does not know of the obscure information.
  • Appeal to Popularity: Claiming something is true because many or most people believe it.
  • Appeal to Tradition: Claiming something is superior to something else because the first is older.
  • 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.
  • 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.
  • Because I Said So: A variant of Appeal to Authority, this fallacy is more formally known as Proof by Assertion. This fallacy posits that something is true or false, right or wrong, simply because the speaker says so, shutting down anyone who asks them why this is the case.
  • 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. Such an argument can be simplified down to "it's true because it's true."
  • Confirmation Bias (also known as cherry-picking): Presenting or accepting only data that supports your predetermined position and ignoring data that damages your position.
  • Converse Error: (part of "Correlation does not imply causation.") Concluding that a certain set of results can only come from one set of circumstances. "If A, then B. B, therefore A."
  • Enemy Mine: When it is assumed that two beliefs that share a dislike for a third one must be compatible, because the two are on the same "side".
  • Everything Except Most Things: A generalization with so many exceptions that what remains is less than impressive, if useful at all.
  • 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 (False Syllogism): "God is love. Love is blind. Stevie Wonder is blind. Therefore, Stevie Wonder is God."
  • Gambler's Fallacy: Thinking that previous random events will have an effect on future random events, when in reality the odds are the same regardless of the amount of times such a random event has taken place. "The odds of winning are 1:20. I've played 19 times, so I'm due for some good luck!"
  • Golden Mean Fallacy: Thinking that the "middle ground" between two extreme points is necessarily the best option, simply because they are extremes. "Hitler says to kill all the Jews, Rabbi Bernstein says to kill none of the Jews, therefore the correct answer is to kill half the Jews."
  • Hard Work Fallacy ("If I can do it, so can you."): The assumption that individual effort is the only thing needed to succeed, regardless of any other factors.
  • Hitler Ate Sugar: A species of the Association Fallacy. Claiming something is bad because an evil person (like Hitler) liked it, or inversely claiming something is good because they were against it.
  • 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.
  • Let's 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.
  • Made Out to Be a Jerkass: Acting in self-defense makes the actual victim considered to be the jerk, and the offender is sympathized with and defended.
  • 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.
  • 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, or changing something's definition after it's already been defined.
  • Original Position Fallacy: Advocating something because one assumes that they will themselves benefit from it or don't think they'll suffer the consequences of it. People advocating systems they think they're going to benefit from usually have only their own interest in mind, and will typically object to extending the same benefit to others.
  • 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.
  • Perfect Solution Fallacy: Rejecting an idea because it doesn't solve all addressed issues. "If we can't fix it perfectly, we shouldn't try at all."
  • Poe's Law: Satire mistaken for fact, used by someone who states it as fact. Or, alternatively, sincere expression of a (seemingly ludicrous) belief mistaken for satire.
  • 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.
  • Sharpshooter Fallacy: Claiming that a conclusion is inevitable after the specific results have already been witnessed; using the same data to generate both a hypothesis and a conclusion. Named for a hypothetical scenario where someone shoots a bullet into a wall, then paints a target around it.
  • Slippery Slope Fallacy: Claiming that an action will inevitably lead to another, very unacceptable action. "If X, then eventually Y."
  • 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.
  • Survivorship Bias: Overemphasizing 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."
  • When Is Purple: Going beyond "comparing apples to oranges" by thinking of the color orange as an apple.
  • With Us or Against Us: A form of false dilemma. Assuming that not openly supporting one side means you oppose them (or vice-versa).