Classifying Informal Logical Fallacies

What I’m after here is not a dictionary of the fallacies with perfect definitions, but rather, by placing like with like, a systematisation of them, as far as this is possible. I try not to contradict anything done by established experts. I’d like to have good definitions and examples too, time permitting. update 26/04/2011

Something interesting to me is that in manipulating these categories diagrammatically, under multiple constraints, an insight “fell out” of the process – the grouping below False Dilemma, which I will soon change to an overall term of “Bifurcation” – as fallacies, they all play upon, or maybe even prey upon, the tendency of the human mind to think in opposites. 30/04/2011

Fallacies – Informal – an informal fallacy, as opposed to a formal fallacy, is a type of fallacy in which the content of the argument is relevant to its fallaciousness, or which is fallacious for epistemological, dialectical, or pragmatic reasons.

FALLACIES OF PRESUMPTION unsound arguments involving unfounded or unproven assumptions contained within the premises. Includes begging the question, argument from ignorance, false cause, generalisation, complex question and ignoratio elenchi.

Petitio principii

petitio principii        (begging the question). This is the fallacy of assuming, when trying to prove something, what it is that you are trying prove. For all practical purposes, this fallacy is indistinguishable from circular argumentation.

circulus in demonstrando        (circular argument). Circular argumentation occurs when someone uses what they are trying to prove as part of the proof of that thing.

circular argument        circulus in demonstrando

circulus in probando        circulus in demonstrando

vicious circle        begging the question

begging the question        also known as petitio principii, circulus in probando, circular argument, vicious circle

question-begging analogy        an analogical argument begs the question when the strength of the analogy depends upon some controversial point at issue.

False Analogy relates to metaphor

false analogy        A is like B. B has property P. Therefore, A has property P. (Where the analogy between A and B is weak.)

weak analogy          false analogy

faulty analogy        false analogy

questionable analogy        false analogy

Generalisation relates to synecdoche

dicto simpliciter        A dicto simpliciter ad dictum secundum quid. Sweeping generalisation.

sweeping generalisation        A dicto simpliciter ad dictum secundum quid

hasty generalisation        fallacy committed when a person draws a conclusion about a population based on a sample that is not large enough

converse accident        hasty generalisation

biased sample        fallacy committed when a person draws a conclusion about a population based on a sample that is biased or prejudiced in some manner

unrepresentative sample        biased sample

misleading vividness        a fallacy in which a very small number of particularly dramatic events are taken to outweigh a significant amount of statistical evidence

spotlight        committed when a person uncritically assumes that all members or cases of a certain class or type are like those that receive the most attention or coverage in the media

Volvo fallacy        when the vividness of a recent memory, or the strikingness of an unusual event, leads one to overestimate the probability of events of that type occurring, especially if you have better evidence

fallacy of significance        an assertion which seems to have an importance to the point at issue, but which does not.

fallacy of accident     

False Cause relates to metonymy

non causa pro causa        false cause

false cause        non causa pro causa. This is the most general fallacy of reasoning to conclusions about causality.

cum hoc ergo propter hoc        (with this, therefore because of this). This is the familiar fallacy of mistaking correlation for causation — i.e., thinking that because two things occur simultaneously, one must be a cause of the other.

post hoc ergo propter hoc        (after this, therefore because of this). This is the fallacy of assuming that A caused B simply because A happened prior to B.

post hoc        a fallacy with the following form: A occurs before B. Therefore A is the cause of B.

confusing cause and effect        a fallacy that has the following general form:  A and B regularly occur together. Therefore A is the cause of B.

ignoring a common cause        fallacy having the following general structure: A and B are regularly connected (but no third, common cause is looked for). Therefore A is the cause of B.

questionable cause        this fallacy has the following general form: A and B are associated on a regular basis. Therefore A is the cause of B.


argumentum ad ignorantiam        (argument to ignorance). This is the fallacy of assuming something is true simply because it hasn’t been proven false.

argument from ignorance        also known as Argumentum ad Ignorantiam. There is no evidence against p. Therefore, p.

Burden of Proof        a fallacy in which the burden of proof is placed on the wrong side

False Dilemma

black-and-white fallacy        a fallacy in which a person uses the following pattern of “reasoning”: Either claim X is true or claim Y is true (when X and Y could both be false). Claim Y is false. Therefore claim X is true.

black-or-white fallacy        black-and-white fallacy

either / or fallacy        black-and-white fallacy

false dilemma        a fallacy in which a person uses the following pattern of “reasoning”: Either claim X is true or claim Y is true (when X and Y could both be false). Claim Y is false. Therefore claim X is true.

bifurcation        black-or-white fallacy

Slippery Slope

slippery slope        a slippery slope fallacy is an argument that says adopting one policy or taking one action will lead to a series of other policies or actions also being taken, without showing a causal connection between the advocated policy and the consequent policies.

argument of the beard          slippery slope

thin end of the wedge          slippery slope

Middle Ground        fallacy committed when it is assumed that the middle position between two extremes must be correct simply because it is the middle position

argumentum ad temperantiam

Complex Question

plurium interrogationum        many questions

many questions        plurium interrogationum: “many questions”, Latin   complex question

complex question        a complex question is a question that implicitly assumes something to be true by its construction

loaded question        complex question

FALLACIES OF AMBIGUITY relates to language / puns

fallacy of ambiguity        as a logical fallacy, ambiguity occurs when linguistic ambiguity causes the form of an argument to appear validating when it is not. Includes equivocation, amphiboly, composition and division.

ambiguous middle        any valid form of categorical syllogism with an ambiguous middle term.

equivocation        based on ambiguity of a word or phrase (lexical rather than grammatical)

doublespeak        equivocation

amphiboly / amphibology        ambiguity resulting from ambiguous grammar. The fallacy of Amphiboly occurs when a bad argument trades upon grammatical ambiguity to create an illusion of cogency

accent        ambiguity by accents used to indicate pronunciation

fallacy of emphasis or accent        incorrect emphasis of the words in a sentence. Improper stress is placed on some portion of a premise or conclusion so the meaning of the argument is distorted.

scope fallacy        ambiguity based on scope. Logical terms such as “not” have a scope, that is, a part of the proposition in which they occur that they affect logically.

vagueness        the fallacy of vagueness occurs only when the appearance of soundness in an argument depends upon vagueness in its terms.


relates to example and emotional

argumentum ad populum        (argument or appeal to the public). This is the fallacy of trying to prove something by showing that the public agrees with you.

argumentum ad numerum        (argument or appeal to numbers). This fallacy is the attempt to prove something by showing how many people think that it’s true

bandwagon fallacy        the bandwagon fallacy is committed whenever one argues for an idea based upon an irrelevant appeal to its popularity.

argument by consensus        bandwagon fallacy

authority of the many        bandwagon fallacy

appeal to belief        a fallacy that has this general pattern: Most people believe that a claim, X, is true. Therefore X is true.

appeal to common practice        a fallacy with the following structure:  X is a common action. Therefore X is correct/moral/justified/reasonable, etc.

argumentum ad verecundiam        (argument or appeal to authority). This fallacy occurs when someone tries to demonstrate the truth of a proposition by citing some person who agrees, even though that person may have no expertise in the given area.

ipse dixit        (“He, himself, said it”, Latin) Appeal to misleading authority

argumentum ad antiquitatem        (the argument to antiquity or tradition). This is the familiar argument that some policy, behaviour, or practice is right or acceptable because “it’s always been done that way.”

appeal to novelty        a fallacy that occurs when it is assumed that something is better or correct simply because it is new

naturalistic fallacy        this is the fallacy of trying to derive conclusions about what is right or good (that is, about values) from statements of fact alone.

appeal to nature        this is the fallacy of assuming that whatever is “natural” or consistent with “nature” (somehow defined) is good, or that whatever conflicts with nature is bad.

relativist fallacy        committed when a person rejects a claim by asserting that the claim might be true for others but is not for him/her

argumentum ad consequentiam        arguing that a proposition is true because belief in it has good consequences, or that it is false because belief in it has bad consequences is often an irrelevancy.

appeal to consequences of a belief        X is true / false because if people accept / do not accept X as being true / false then there will be positive / negative consequences. Also includes wishful thinking.

wishful thinking        as a logical fallacy, wishful thinking is an argument whose premise expresses a desire for the conclusion to be true.

argumentum ad baculum        appeal to force. The name “argumentum ad baculum” alludes to the use of a stick, or club, to beat someone.

argument from force        a technique of distraction which occurs when force, or the threat of force, is used to “win” a debate. More frequently, it is used to cover up the fact that the threatener is losing.

argumentum ad nauseam        (argument to the point of disgust; i.e., by repetition). This is the fallacy of trying to prove something by saying it again and again.


emotional appeal        a type of argument which attempts to arouse the emotions of its audience in order to gain acceptance of its conclusion

appeal to emotion        a fallacy with the following structure: Favorable emotions are associated with X. Therefore, X is true.

argumentum ad metum        appeal to fear. A fallacy with the following pattern:  Y is presented (a claim that is intended to produce fear). Therefore claim X is true (a claim that is generally, but need not be, related to Y in some manner).

appeal to fear        argumentum ad metum

argumentum ad odium        appeal to hatred

argument from hatred        also known as Argumentum ad Odium

argumentum ad misericordiam        argument or appeal to pity

appeal to spite        a fallacy in which spite is substituted for evidence when an “argument” is made against a claim

argumentum ad superbium        appeal to pride

argument from pride        also known as Argumentum ad Superbium

appeal to flattery        a fallacy of the following form: Person A is flattered by person B. Person B makes claim X. Therefore X is true.

argumentum ad invidiam        argument from envy.

argument from envy        also known as Argumentum ad Invidiam

appeal to ridicule        a fallacy in which ridicule or mockery is substituted for evidence in an “argument.”

Argumentum ad Hominem

genetic fallacy        a line of “reasoning” in which a perceived defect in the origin of a claim or thing is taken to be evidence that discredits the claim or thing itself, or origin as evidence for the claim

argumentum ad hominem        (argument directed at the person). This is the error of attacking the character or motives of a person who has stated an idea, rather than the idea itself.

circumstantial ad hominem        a fallacy in which one attempts to attack a claim by asserting that the person making the claim is making it simply out of self interest

personal attack        when a person substitutes abusive remarks for evidence when attacking another person’s claim or claims

poisoning the well        trying to discredit what a person might later claim by presenting unfavorable information (be it true or false) about the person

guilt by association        a fallacy in which a person rejects a claim simply because it is pointed out that people she dislikes accept the claim

bad company fallacy        guilt by association – the attempt to discredit an idea based upon disfavored people or groups associated with it.

the company that you keep fallacy        guilt by association

tu quoque (ad hominem tu quoque)        (“you too”). This is the fallacy of defending an error in one’s reasoning by pointing out that one’s opponent has made the same error.

two wrongs make a right        a fallacy in which a person “justifies” an action against a person by asserting that the person would do the same thing to him/her, when the action is not necessary to prevent B from doing X to A

special pleading        a fallacy in which a person applies standards, principles, rules, etc. to others while taking herself (or those she has a special interest in) to be exempt, without providing adequate justification for the exemption

Straw Man        this is the fallacy of refuting a caricatured or extreme version of somebody’s argument, rather than the actual argument they’ve made.

Red Herring

ignoratio elenchi        (“ignorance of refutation”, Latin) red herring

red herring        introducing irrelevant facts or arguments to distract from the question at hand

irrelevant thesis        ignorantio elenchi, red herring


Loaded Language

loaded language / words        a word or phrase is “loaded” when it has a secondary, evaluative meaning in addition to its primary, descriptive meaning.

question-begging epithets        loaded language / words

one-sidedness        a one-sided case presents only evidence favouring its conclusion, and ignores or downplays the evidence against it.

one-sided assessment        one-sidedness

suppressed evidence        one-sidedness. ignoring the counterevidence

slanting        one-sidedness. related to bias.

card stacking        ignoring the counterevidence; one-sidedness

Quoting out of Context

quoting out of context        to quote out of context is to remove a passage from its surrounding matter in such a way as to distort its meaning.

abstraction        quoting out of context

Gambler’s Fallacy

gambler’s fallacy        a fallacy committed when a person assumes that a departure from what occurs on average or in the long term will be corrected in the short term

Monte Carlo fallacy        gambler’s fallacy

regression / regressive fallacy        the regression fallacy occurs when one mistakes regression to the mean for a causal relationship.

Texas Sharpshooter fallacy        this fallacy occurs when someone jumps to the conclusion that a cluster in some data must be the result of a cause, usually one that it is clustered around.

Composition relates to synecdoche

composition        a fallacy committed when a conclusion is drawn about a whole based on the features of its constituents when, in fact, no justification is provided for the inference

division        a fallacy committed when a person infers that what is true of a whole must also be true of its constituents and justification for that inference is not provided

False Precision

false precision        this fallacy occurs when an argument treats information as more precise than it really is.

misplaced precision        false precision

fake precision        false precision

spurious accuracy        false precision


About David Ruaune

My main interests are philosophy, psychology and semiotics.
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