Bronze-level articleLogical fallacy

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A logical fallacy is an error in logic that prevents an argument from being valid. Fallacious logic, however, does not prevent people from being swayed by said argument.


[edit] Explanation

Logical fallacies come from human intuition. A logical fallacy is not necessarily a Bayesian fallacy, so given a particular circumstance, jumping to the conclusion will be more likely than not, and get baked into human thinking as a heuristic. When the heuristic is applied outside its reasonable bounds, it becomes a cognitive bias.

The problem is that this can lead to you being grievously wrong about reality. So you may form an opinion by a heuristic (System 1 thinking), but you need to show your working to make sure you haven't just said something silly (System 2 thinking).

This particularly applies to thinking about science, because scientific thinking is unintuitive for most people unless trained into it; and to arguing your points in general, because heuristics are full of glaring exceptions.

[edit] Types

[edit] Formal

A formal fallacy is a syllogism in which, regardless of the truth of the terms, the conclusion does not follow (ie, the syllogism is invalid). It has many subfallacies:

  1. Affirmative conclusion from a negative premise: Asserting some positive fact from negative premises.
  2. Affirming a disjunct: The formal fallacy: from A-> B and B to infer A. The inverse of the valid affirming the antecedent: from A -> B and A to infer B.
  3. Affirming the consequent: If A implies B, and B, therefore A.
  4. Chewbacca Defense: A logically invalid Gish Gallop intended to confuse.
  5. Confusion of the inverse: Confusing the probability of a set of data given a hypothesis, and the probability of a hypothesis given a set of data.
  6. Denying the antecedent: If A implies B, and not-A, therefore not-B.
  7. Enthymeme: When an unstated premise is necessary for logical validity.
  8. Existential assumption: When the conclusion of a syllogism requires that a class has at least one member, but one or more of the premises do not.
  9. Fallacy fallacy: The meta-fallacious argument that your opponent (or someone arguing for a similar point) has used logical fallacies, therefore the argument is wrong.
  10. False dilemma: When two opposing views are presented as the only options, but are not.
  11. Four-term fallacy: Any syllogism in which four terms are present, instead of the mandatory three.
  12. Illicit process: Incorrectly concluding for all of a set when the premises apply to only some of a set. Specificially, the illicit major and illicit minor.
  13. Negative conclusion from affirmative premises: Asserting some negative fact from positive premises.
  14. Negative proof: Arguing that something must exist because there is no evidence it does not exist.
  15. Not even wrong: An answer that is utterly unrelated to the question.
  16. Self-refuting idea: A claim that on closer inspection disagrees with itself.
  17. Substituting explanation for premise: Asserting that, because a given explanation for why something occurs is bad, the thing does not occur.
  18. Syllogistic fallacy: Any instance in which a syllogism with incorrect structure is used.

[edit] Informal

An informal fallacy in which the conclusion would not follow if the terms were true (ie, some premise is incorrect). It has many subfallacies.

  1. Ad hoc: When some idea is asserted purely to shore up some other idea.
    1. Argumentum ex culo: When some fact is cited to defend something, but is entirely fictional.
    2. Escape hatch: When some rhetorical technique is used to
    3. Handwave: When some fact that defeats an argument is ignored.
    4. Moving the goalposts: When truth is redefined on the spot.
    5. No True Scotsman: When groups are redefined on the spot.
    6. Special pleading: When universal rules no longer apply in this specific instance.
  2. Ad hominem: When an arguer is attacked, rather than their idea.
    1. Ad iram: When an arguer's supposed anger is used to disprove their ideas.
    2. Appeal to bias: When an arguer's supposed mental bias is used to disprove their ideas.
      1. Shill gambit: Asserting an arguer is working for someone and spreading disinformation.
    3. Argumentum ad cellarium: Accusing the arguer of still being in "mom's basement".
    4. Association fallacy: When someone's associations are used as evidence against their ideas.
    5. Blaming the victim: When a victim's actions are used as proof that some offense against them was justified.
    6. Damning with faint praise: When someone is attacked through praise of an achievement that isn't praiseworthy or isn't significantly praiseworthy, suggesting that no achievements worthy of praise exist.
    7. Demonization: When one's opponent is depicted as unequivocally terrible.
      1. Poisoning the well: Where an opponent is pre-painted as terrible.
      2. Dixiecrat fallacy: Dems supported segregation! Dems are racist!
    8. Fallacy of opposition: When someone's opposition to your opinion is taken as proof of their incorrectness.
      1. Bulverism: Arguing about how someone got such bad ideas, rather than that the ideas are bad.
      2. Jonanism: Considering all people who disagree with you as the same person (or following the same ideas).
    9. Genetic fallacy: When the source of an argument is attacked, rather than its merits.
    10. Nutpicking: When a few extremists from a group are taken as representative of the group.
    11. Tu quoque: Where a criticism is falsely dismissed because its author is also guilty of the charge.
      1. Whataboutism: Tu quoque, USSR style!
    12. Scapegoat: Using someone to take the blame.
  3. Argument from ignorance: When it is claimed that the truth of a premise is based on the fact that it has not been proven false or proven true.
    1. Argument from incredulity: Literally "that's unbelievable = that's obviously not real". This kind of thinking would quickly put an end to virtually all quantum physics.
    2. Argument from silence: The lack of response to my point makes my point correct!
      1. Argument by censorship: I have created silence; this shows that my point cannot be responded to!
    3. Science doesn't know everything: And therefore it knows nothing.
    4. Science was wrong before: And therefore it can never be right.
    5. Toupee fallacy: I have never seen a toupee that I could not recognize as a toupee.
    6. Willful ignorance: *fingers in ears* nah-nah-nah-nah-nah, can't heeeeaaaarrrr youuuu!
  4. Causalation: When something is not truly the cause of an effect.
    1. Confusing correlation for causation — The number of pirates on the seas has gone down, this correlates with global temperatures rising. So, do pirates cause global cooling?
    2. Gambler's fallacy: I lost the last twenty dice rolls -- I'm due for a win, so I better double down!
    3. Post hoc, ergo propter hoc: Because event A happened before B, A must have caused B.
    4. Wrong direction: When a cause is mistakenly considered an effect.
  5. Emotional appeal: Evaluating an argument based on its emotional consequences rather than logical ones.
    1. Appeal to confidence: Trust me, I know what I'm doing.
    2. Argument from consequences: Arguing against a point's truth based on expected negative outcome.
      1. Argumentum ad baculum: A subset of arguing from adverse consequences, the negative outcomes are being actualised by the one making the argument.
    3. Appeal to fear: We're surrounded by logical fallacies! RUN!!
    4. Appeal to flattery: What a lovely fallacy you have there! You must be a smart person, someone who'd find quantum healing quite fascinating.
    5. Appeal to gravity: I'm the only one up here who takes this seriously. Disregard these jokers -- I have the truth.
    6. Appeal to money: I'm telling the truth. How else could I have gotten all this money?
    7. Appeal to shame: Would you say that in front of your mother?
    8. Argumentum ad fastidium: Ugh, that's so gross -- it must be false.
    9. Deepity: something something children of the stars, something something love is more than just chemicals
    10. Tone argument: If you can't keep it civil, you clearly can't make truthful statements!
  6. Fallacy of ambiguity: Purposefully making something unclear, to allow its misuse.
    1. Etymology: Confusing the original meaning of a word and its current meaning.
    2. Equivocation: Deliberately substituting the meaning of a given word in one context for another context that is inappropriate in order to make your argument.
    3. Fallacy of accent: When the meaning of a text is changed by what word or words are stressed, and stress is unclear.
    4. Fallacy of amphiboly: When a sentence, because of its grammar, structure, or punctuation, can be interpreted in multiple ways.
    5. Loaded language — Asking a question, which has an assumption built into it, so that it can't be answered without appearing to agree to the assumption, or else appearing evasive by questioning the assumption. To be distinguished from a Leading question, which is not a fallacy, but is a way of suggesting the desired answer by how the question is phrased. "Are you still beating your wife?" is a loaded question, for it assumes that at one time you did beat your wife; while "You weren't beating your wife, were you?" is a leading question, for it suggests the simple answer no.
    6. Masked man fallacy: When Leibniz's law is used improperly.
    7. Moral equivalence: Arguing that two things are morally equal, even though they are different things.
      1. Not as bad as: A moral equivalence fallacy that says because B is worse than A, A is justified. Also known as the 'not as bad as' fallacy.
    8. Phantom distinction: When someone spends time arguing for the superiority of one term over another (rather than the intended debate), yet there is no effective difference.
    9. Quote mining: Misquoting someone to gain the appearance of authority.
    10. Scope fallacy: When the scope of a logical operator (eg, "not", "some", or "all") is vague allows misinterpretation and incorrect conclusions.
    11. Style over substance fallacy: Using language or rhetoric (ethos or pathos) to enhance the appeal of an argument, but not its validity, or arguing the method of presentation affects the truth of a claim.
    12. Suppressed correlative: Attempting to redefine two mutually exclusive options so that one encompasses the other.
    13. Wronger than wrong: The fallacy of assuming that different degrees of "wrong" are the same.

[edit] Conditional

A conditional fallacy may or may not be fallacious, conditional on whether or not one of their premises is accepted. It has many subfallacies:

  1. Appeal to authority: incorrectly asserts that some authority's assertion proves a point. It has several subfallacies:
    1. Anonymous authority: When a source is quoted (or supposedly quoted), but no name is given.
    2. Appeal to celebrity: When a source is supposedly authoritative because of the respect people give them.
    3. Appeal to confidence: When a source is supposedly authoritative because of their confidence.
    4. Argumentum ad populum: When a source is supposedly authoritative because of their popularity.
      1. Silent Majority: When a source is supposedly authoritative because of the popularity of their views, yet there is no evidence of the popularity of their views.
    5. Invincible authority: When a source is the entirety of an argument.
    6. Ipse dixit: When a source is the person making the argument.
    7. Linking to authority: When a source is "cited" in-text yet the reference doesn't exist / is irrelevant / says something else.
    8. Ultracrepidarianism: When a source is quoted outside their expertise, as if expertise in one field extended to another.
      1. Professor of nothing: When a source is introduced as "Prof." or "Dr.", yet they aren't.
    9. Quote-mined authority: When an authority is selectively quoted to distort their views.
  2. Slippery slope: But if we legalize rabbit hunting, then pretty soon we may legalize human hunting!
    1. Continuum fallacy: Asserting that a continuum of possibilities between two distinct states renders the states identical.
  3. Special pleading: Your evidence might disprove my example, but my example is special.
  4. What's the harm: It's just some water (and your payment of $50); what harm can it do?
  5. Imprecision fallacy: When data is specific to something that doesn't apply to what is claimed.
    1. Anecdotal evidence: Using anecdotal evidence to make a general point.
      1. Generalization from fictional evidence: Using a fake story to make a general point.
    2. Apex fallacy: Using the best/worst group to generalize to the whole group.
    3. Argument from analogy: Using an ill-fitting analogy to generalize a group.
      1. Extended analogy - Arguing an opponent's analogy that A is like B in one particular way is a claim that A and B are directly comparable to one another.
    4. Category mistake: Confusing what is true of a part with what is true of the whole.
    5. Cherry picking: Using examples that support your viewpoint.
    6. Nutpicking: Using examples that are batshit insane to represent a group.
    7. Overgeneralization: Taking a few specifics and making a general rule out of them, without the few specifics adequately representing the entire group.
    8. Overprecision: Assuming a prediction is exactly correct for any given point.
    9. Pragmatic fallacy: It worked for me -- it'll work for everyone!
    10. Selection bias: Bias inherent in selecting data.
    11. Spotlight fallacy: Assuming aspects of a group from aspects from a smaller observed part of the group.
    12. Texas sharpshooter fallacy: A data mining fallacy and pattern recognition error where the arguer makes an ad hoc conclusion from a set of unrelated data without looking for corroborating data.

[edit] Argumentative

Fallacious argument styles occur when one speaker uses certain tactics to attempt to prevent honest and useful discourse.

Fallacy misidentifications occur when one speaker doesn't know what they're talking about, while also attempting to claim something's a logical fallacy.

For example, a Gish Gallop involves spewing so many arguments out that the opponent cannot respond to them. Because the opponent failed to respond to every point, the Galloper can argue that they have won the debate. However, this is fallacious; even though not every point was responded to, this does not mean that the points which went unrebutted were true; instead, the tactic merely showed that the respondent needed more time.

[edit] Must be used in argument

One common error when first learning about logical fallacies is to fail to realise that a fallacy can only be present if it is used as part of an argument: for example, "you are an idiot" is not an ad hominem fallacy because it is simply a blank statement: "you are an idiot, therefore you are wrong" is an ad hominem because a conclusion is being drawn. Further, "you are saying idiotic things, therefore you are an idiot" is a valid argument regardless of whether the premise (the opponent is saying idiotic things) is true. However, it is only a sound argument in the event the premise is true.

[edit] Validity versus truth

Just because an argument is valid does not mean the conclusion is true. A valid argument simply means that if the premises are true, the conclusion must be true as well. A sound argument is a valid argument with the additional requirement that the premises (and thus the conclusion) are true. For instance, consider the following argument.

P1: All humans are cows.
P2: All cows are plants.
C1: All humans are plants.

Although the conclusion is false and the premises are false, this is still a valid argument because if the premises were true, the conclusion must be true as well. Since at least one premise is false, the argument is valid but not sound.

[edit] Common examples

  • One single proof — Dismissing all circumstantial evidence in favor of a single "smoking gun" that may not (and may not need to) exist.
  1. Argument by assertion — The belief that if you say something enough times, it eventually becomes true and therefore you win the argument.
    1. Argumentum ad nauseam — The belief that something becomes true if repeated often enough to make you vomit (see also Gish Gallop and Chewbacca Defense).
  2. Great Beethoven fallacy
  3. Red herring — A group of fallacies which bring up a fact which is irrelevant to the issue, in an attempt to distract the opponent and/or audience.
  4. Straw man — Distorting an opponent's position for greater rhetorical flexibility.
  5. Argumentum ad lapidem — Dismissing a statement as absurd without giving proof of its absurdity.
  6. Appeal to ancient wisdom — It's right because the Maya/Chinese/Hebrews said it thousands of years ago!
  7. Appeal to tradition — Just because it's always been that way doesn't mean it's the right way.
  8. Argumentum ad populum or bandwagon — Arguing for a point based on popularity rather than merit.
  9. Galileo gambit — If someone is going against the tide of popular thinking, they must be right because the likes of Galileo were right, while in reality, Galileo was right because he had evidence (see also Argumentum ad martyrdom).
  10. Balance fallacy — Giving equal weighting to both sides of an argument, even if one really doesn't deserve the time.
  11. Argumentum ad Hitlerum — Saying something is bad because Hitler did it.
  12. Intuition pump — Deliberately abusing a thought experiment to prove a fallacious point.
  13. My enemy's enemy — Supporting someone because you've a mutual enemy with them.
  14. Nirvana fallacy — Claiming that a realistic solution is useless because it is not as good as an idealized perfect solution.
  15. Presupposition — Making an implicit assumption as part of an argument.
  16. Reductio ad absurdum — Following a chain of thought to its absurd or contradictory conclusion. Sometimes worthwhile, but oftentimes fallacious.
  17. Slothful induction — Ignoring the strongest conclusion of an inductive argument to focus on a weaker one.
  18. Appeal to novelty — Arguing that a claim is valid because it is novel.
  19. Appeal to nature — Arguing that something is good because it is "natural" (see also Moralistic fallacy).

[edit] See also

Icon fun.svg For those of you in the mood, RationalWiki has a fun article about Justification generator.

[edit] External links

[edit] Fallacy collections

There are lots of fallacy collections in the Web. Some of them promote a particular agenda, but most fallacies listed in them are real and present in arguments everyday. Unfortunately, many are deprecated.

Here is a list of websites, ordered by usefulness:

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