Logical fallacy

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A logical fallacy is an error in the logic of an argument [1][2] that prevents it from being logically valid but does not prevent it from swaying people's minds.

Logical fallacies come from human intuition. A logical fallacy is not necessarily a Bayesian fallacy [3], so given a particular circumstance, jumping to the conclusion will be more likely than not, and get baked into human thinking as a heuristic [4]. 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 [5]. 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] Explanation

See the main article on this topic: Syllogism

[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 [6]. For example, "So-and-so is a socialist" is not an ad hominem fallacy (see below) because it is simply a statement. So-and-so may be a socialist. "So-and-so is a socialist, therefore s/he is wrong" is an ad hominem because a conclusion is being drawn, and the conclusion has nothing to do with the premise. It attacks the opponent; not the opponent's argument. This can be more complicated than it sounds, however, because the conclusion that s/he is wrong is often implied.

Likewise, "You are an idiot" is not an argument - it is a statement - but it implies your argument is idiotic. Further, "you are saying idiotic things, therefore you are an idiot" may be 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, and if "saying idiotic things" makes one an idiot. (Even geniuses have said idiotic things. Just ask their spouses.)

[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 [7]. A sound argument is a valid argument with the additional requirement that the premises (and thus the conclusion) are true [8]. 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 [9].

[edit] Fallacy-dropping

What we have here is a blatant example of argument by assertion (http://rationalwiki.org/wiki/Argument_by_assertion). It's therefore clear your mother was a whore, and you flunked out of elementary school. </every_pretentious_redditor_ever>
—Colonel Custer[10]

It is not acceptable to merely state that one's opponent is using a fallacy (as above). One must explain how the opponent's argument is fallacious (eg, they claim that you are a shill), why it is wrong (there's no evidence that you are a paid government disinformation agent), and what that means for their argument (if you're not a shill, then your arguments can't be hand waved away) [11].

This need not be a drawn-out paragraph. Even "your ad hominem is irrelevant to my argument, so my argument stands" is sufficient.

Otherwise, one runs into the risk of fallacy dropping -- claiming someone's argument is wrong without bothering to explain why -- which comes dangerously close to ad hominem. (It's equivalent to shouting "your logic is bad!" and claiming victory.)

[edit] Types

There are several methods of grouping fallacies. RationalWiki categorizes fallacies into four groups:

  1. Formal fallacy: An argument in which the conclusion would not be true whether or not its premises are correct, because it does not follow valid logical structure.
  2. Informal fallacy: An argument in which the conclusion would be true if the premises were true, but those premises are almost always incorrect.
  3. Conditional fallacy: An argument which may or may not be fallacious, conditional on whether or not one of its premises is true. For example, an argument from authority can be fallacious when the authority isn't authoritative, but can be valid when there's reason to trust the source.
  4. Fallacious argument style: An argument in which one speaker uses unfair, manipulative, or disruptive tactics to prevent actual discussion of the issue.

[edit] Formal

See the main article on this topic: Formal fallacy
  1. Affirmative conclusion from a negative premise: Asserting some positive fact from negative premises.
  2. Affirming a disjunct: A or B, A, therefore not-B.
  3. Affirming the consequent: If A implies B, and B, therefore A. The inverse of the valid affirming the antecedent: from A -> B and A to infer B.
  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

See the main article on this topic: Informal fallacy
  1. General:
    1. Appeal to ancient wisdom: It's right because the Maya/Chinese/Hebrews said it thousands of years ago!
    2. Appeal to tradition: Because it's always been that way, it's absolutely the right way!
    3. Balance fallacy — Giving equal weighting to both sides of an argument, even if one really doesn't deserve the time.
    4. My enemy's enemy — Supporting someone because you've a mutual enemy with them.
    5. Reductio ad absurdum — Following a chain of thought to its absurd or contradictory conclusion. Sometimes worthwhile, but oftentimes fallacious.
    6. Appeal to novelty — Arguing that a claim is valid because it is novel.
    7. Appeal to nature — Arguing that something is good because it is "natural" (see also Moralistic fallacy).
  2. 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 evade the burden of proof.
    3. Handwave: When some fact that defeats an argument is ignored.
    4. Moving the goalposts: When truth is redefined on the spot.
    5. Nirvana fallacy: Claiming that a realistic solution is useless because it is not as good as an idealized perfect solution.
    6. No True Scotsman: When groups are redefined on the spot.
    7. Slothful induction: Ignoring the strongest conclusion of an inductive argument to focus on a weaker one.
    8. Special pleading: When universal rules no longer apply in this specific instance.
  3. 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.
  4. 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!
  5. 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.
  6. 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!
  7. Circular reasoning: Ironclad and impermeable self-supporting logic.
    1. Argumentum ad dictionarium: If the dictionary says what I think something means,the dictionary is right. If not, find a new dictionary.
    2. Argument by assertion: If you say something enough times, it eventually becomes true and therefore you win the argument.
      1. Argumentum ad nauseam: If you say something often enough to make people vomit, you win.
      2. Infinite regress: If I say X, and then say that X proves that X is true, then I win!
    3. Appeal to faith
    4. Self-refuting idea: If I need to explain why my theory is wrong, I'll just introduce a new theory that entirely cancels out my old theory.
  8. 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

See the main article on this topic: Conditional fallacy
  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

  1. 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).
  2. Intuition pump — Deliberately abusing a thought experiment to prove a fallacious point.
  3. One single proof — Dismissing all circumstantial evidence in favor of a single "smoking gun" that may not (and may not need to) exist.
  4. 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.
  5. Straw man — Distorting an opponent's position for greater rhetorical flexibility.
  6. Argumentum ad Hitlerum — Saying something is bad because Hitler did it.

[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 roughly by usefulness:

  1. Fallacy Files(link)
    1. Taxonomy of Logical Fallacies(link)
    2. Glossary(link)
    3. What is a logical fallacy?(link)
  2. Your Logical Fallacy Is(link)
  3. International Encyclopedia of Philosophy(link)
  4. Secular Web(link)
  5. Nizkor Project(link)
  6. Skeptic's Dictionary(link)
  7. About.com: Agnosticism/Atheism(link)
  8. Arthur Schopenhauer(link)
  9. Stephen's Guide to the Logical Fallacies(link)
  10. Dr. Michael LaBossiere(link)
  11. Free Dictionary(link)
  12. Bruce Thompson(link)
  13. Don Lindsay(link)
  14. Art of Debate(link)
  15. George Boeree(link)
  16. Philosophy in Action(link)
  17. Daniel Kies(link)
  18. L. Van Warren(link)
  19. Agent Orange(link)
  20. Humanist Discussion Group(link)

Deprecated ones, listed ad hoc:

  1. Sinclair Community College(link)
  2. Global Tester(link)
  3. Anti-Mormon Illogic(link)
  4. Objectivism(link)
  5. Evolution_V_Creation forums(link)
  6. Peter A. Angeles(link)
  7. Sine Wave(link)
  8. Carleton University(link)
  9. P5(link)
  10. Mathenomicon(link)
  11. Vanessa Hall(link)
  12. J. P. Craig(link)
  13. Informal Fallacies(link)
  14. Autonomist(link)
  15. Gordon, Hanks, & Zhu(link)
  16. Freemasonry(link)
  17. Taking Sides(link)
  18. Jeff Richardson(link)
  19. Chisnell.com(link)

[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] References

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