Logical Fallacies

The following is an incomplete compilation of ways people can and have reasoned incorrectly.

Fallacies of Distraction

Ignoratio elenchi: Latin, meaning "ignorance of refutation". From the Greek ἔλενχος elenchos, meaning an argument of disproof or refutation. Also known as irrelevant conclusion or irrelevant thesis the informal fallacy of presenting an argument that may in itself be valid, but does not address the issue in question.
False dichotomy: False dilemma. Two choices are given when in fact there are more than two.
False presumption: Because something is not known to be true, presume it to be false.
Slippery slope: Claim that a small concession is total surrender.
Complex question: Unrelated points conjoined as a single proposition.
Framing fallacy: Posing a question in a misleading way that if accepted, steers the conclusion. Also called "loaded question".
Kafkatrapping: Accusing someone of something that can't be falsified, then taking protestations of innocence as confirmation of guilt. Term coined by Eric S. Raymond from the novel, The Trial, by Franz Kafka.

Appeals to Emotions instead of Fact or Logic

Appeal to fear: Target is persuaded to agree by threats or force. Argumentum ad baculum ('veiled threat', "to the stick"), or argument based on threat. Argumentum ad metum, appeal to fear.
Appeal to pity: Target is persuaded to agree by sympathy. Argumentum ad misericordiam.
Appeal to envy: Target is persuaded to agree by envy. Argumentum ad invidiam.
Appeal to hatred: Target is persuaded to agree by hatred. Argumentum ad odium.
Appeal to pride: Target is persuaded to agree by pride. Argumentum ad superbium.
Appeal to greed: Target is persuaded to focus on the gains and ignore the risks or costs. Argumentum ad edacitam, rapacitam, avaritiam, greed, rapacity, avarice.
Appeal to ignorance: Target is persuaded to agree if can't prove the contrary. Argumentum ad ignoratium.
Appeal to hope: Such as "What ought to be, is". Quod debet esse, est. Variations include "Dumbo effect" (encouraging belief that holding a feather can enable one to fly) and "placebo effect" (encouraging belief that receiving a treatment will make one feel better).
Consequences: Target is warned of unacceptable consequences.
Prejudicial language: Value or moral goodness is attached to the author or his position.
Bandwagon: A proposition is argued to be true because it is widely held to be true. Appeal to the safety of the herd. Argumentum ad populum, or appeal to the mass opinion of the people.

Fallacy of Authority

Authority: Argumentum ad verecundiam. A proposition is argued to be true because it is supported by experts or authorities. This is widely accepted as a method of argument, but strictly speaking, it is a logical fallacy. Also ipse dixit, "he said it himself".
Recognition: Everyone recognizes the person as an authority, therefore what he says must be true.
Production: The person has done a great deal of authoritative work, therefore he must be an authority.
Power: The person is powerful and successful, therefore he speaks with authority, if only by virtue of his position.
Need implies Have: I have the need to do it, therefore I have the (legal) authority to do it (Necesse ergo praesto). Basis for legal doctrine of "inherent" powers.

Changing the Subject

Attack the Person (ad hominem, "to the man"):
- (1) Attack the person's character.
- (2) Attack the person's circumstances.
- (3) Argue the person does not practise what he preaches. Tu quoque, "You also".
- (4) Attack a person's identity (race, gender, religion), sometimes called Bulverism (named for C.S. Lewis’s imaginary character: Ezekiel Bulver).
Attack the Authority:
- (1) Claim the authority is not an expert in the field.
- (2) Claim experts in the field disagree.
- (3) Claim the authority was joking, drunk, or in some other way not being serious.
Anonymous authority: Cite an authority not named
Chronological snobbery: Ad annis, "to the years". Appealing to the age of something as proof or disproof of its truth.
Style over substance: The manner in which an argument or arguer is presented used as argument to the truth of the conclusion.

Inductive Fallacies

Hasty generalization: The sample is too small to support an inductive generalization about a population. Also called apriorism.
Unrepresentative sample: The sample is unrepresentative of the sample as a whole.
False analogy: The two objects or events being compared are relevantly dissimilar.
Fervent denial: The conclusion of a strong inductive argument is denied despite the evidence to the contrary.
Exclusion: Evidence which would change the outcome of an inductive argument is excluded from consideration.

Fallacies Involving Statistical Arguments

Accident: Apply generalization when circumstances suggest that there should be an exception.
Converse accident: Apply exception in circumstances where a generalization should apply.

Causal Fallacies

Post hoc ergo propter hoc: "After this, therefore because of this". Because one thing preceded another in time, it is held to cause the other.
Joint effect: One thing is held to cause another when in fact they are both the joint effects of an underlying cause.
Insignificant: One thing is held to cause another, and it does, but it is insignificant compared to other causes of the effect.
Wrong direction: The direction between cause and effect is reversed.
Complex cause: The cause identified is only a part of the entire cause of the effect.
Overlooked cause: A cause that will greatly change the effect is ignored.
Overlooked latency: The cause may be correctly identified but is separated from the effect by too long a period of time to support the surrounding argument.
Overlooked change: The effect occurs too slowly to be deemed important. Sometimes called "boiling the frog slowly" (incorrectly, because real frogs will try to get out).
Overlooked nonlinearity: The cause-effect link is nonlinear and is affected by complicated feedback loops.
Treating chaotic system as mechanical: Attributing the effect to causes as though it is predictable, when in fact the system, while parts may exhibit seemingly predictable patterns, cannot be generally predicted in principle from initial conditions.

A common variety of these fallacies is the Rooster Syndrome — giving credit to the rooster crowing for the rising of the sun — but applied to giving credit or blame to leaders for events that occur on their watch to which they made little if any contribution. It may also be called Canute Syndrome or Deification Syndrome, attributing godlike powers to the most powerful figure on the scene.

Missing the Point

Begging the question (petitio principii): The truth of the conclusion is assumed in the premises, or in hidden assumptions. See "complex question", "framing fallacy".
Irrelevant conclusion: An argument in defense of one conclusion instead proves a different conclusion.
Straw man: Misrepresentation. Attack an argument different from (and weaker than) the opposition's best argument.

Fallacies of Ambiguity

Equivocation: Use same term with two or more different meanings. See polysemy, taking advantage of words that have different meanings in different contexts.
Reification: Treat an abstraction as though it were something concrete.
Amphiboly: Use sentence the structure of which allows two different interpretations.
Accent: Emphasis on a word or phrase to suggest a meaning contrary to what the sentence actually says.

Category Errors

Composition: Argue that because the attributes of the parts of a whole have a certain property, therefore the whole has that property.
Division: Argue that because the whole has a certain property, therefore the parts have that property

Non Sequitur

Affirming the consequent: Argument of the form: If A then B, B, therefore A.
Denying the antecedent: Argument of the form: If A then B, Not A, thus Not B.
Inconsistency: Assertion that contrary or contradictory statements are both true.

Syllogistic (Deductive) Errors

Fallacy of four terms: Use a syllogism with four terms.
Undistributed middle: Argue that two separate categories are connected because they share a common property.
Illicit major: Reach conclusion with predicate about all of something when premises only mention some cases of the term in the predicate.
Illicit minor: Reach conclusion with subject of the conclusion about all of something when premises only mention some cases of the term in the subject.
Fallacy of exclusive premises: Use a syllogism with two negative premises.
Affirmative conclusion from negative premise: Reverse the negation.
Enthymeme: Omission of an element of as syllogism as presumed or obvious, which may be logically correct but may also be deceptive, used in persuasive or informal reasoning.
Existential fallacy: Reach particular conclusion from universal premises that don't include an existence premise.
Analogic "syllogism": Reasoning that if A is similar to B, and B is similar to C, therefore A is similar to C. Of course, the relation of "similar" is not transitive, but if the target can be induced to presume it is, this ruse may succeed in persuading. This is a favorite method in the "informal reasoning" used by lawyers.

Fallacies of Explanation

Subverted support: The phenomenon being explained doesn't exist.
Non-support: Evidence for the phenomenon being explained is biased.
Untestability: The theory which explains cannot be tested.
Limited scope: The theory which explains can only explain one thing.
Limited depth: The theory which explains does not appeal to underlying causes.

Fallacies of Definition or interpretation

Too broad: The definition includes items which should not be included.
Too narrow: The definition does not include all the items which should be included.
Failure to elucidate: The definition is more difficult to understand than the word or concept being defined.
Circular definition: The definition includes the term being defined as a part of the definition.
Conflicting conditions: The definition is self-contradictory, an oxymoron.
Ignoring context: Use of language taken in isolation when the meaning is changed by context. See polysemy.
Mismatch: Use of language with either greater or lesser rigor and precision than was used by the original author. common cause of legal misinterpretation.

Fallacies of Misdirection

Red herring: Changing the subject. Claiming an argument is irrelevant when it is, or presenting another argument as relevant that is not.
- Misassociation: For example: A is evil because he did a lot of evil things, and he also did B, therefore B is evil and anyone else who does B is evil. Also a kind of hasty generalization.
Misidentification of cause: For example: The law is being violated, therefore it is defective (violata ergo vitiosa), rather than attributing the failure to the lack of public virtue.
Donkey inference: The proposition is provoking vigorous attacks from the bad guys so it must have merit. From the children's game, "Pin the tail on the donkey."

Fallacies of Miscognition

Compartmentalization: Alternating among multiple, inconsistent concepts with little or no attempt to recognize or reconcile the inconsistencies.
- Kripkean dogmatism: Refusal to engage arguments or evidence inconsistent with one's preferred position.
- Confirmation bias: Seeking information that confirms one's position.
Reductionism: Insistence on concepts that are too simple to account for all the evidence.
- Dichotomic bias: Insistence on recognizing only two alternatives when there are more.
Misforecasting: Insisting that an alternative future flowing from one's decision is available, likely, or desirable, when it is not.

Avoidance of rigor — Sometimes called "generalized logic"

Reductio ad nauseam: One denies the result he is trying to prove, and lists all the consequences of this denial he can think of, and finally announces the result to be established when it actually wasn't.
Reductio ad erratum: One denies the result he is trying to prove, and lists all the arguments he can think of, burying an error in the collection, and finally lifts out the error which appears to have proved the argument but didn't.
Proof by Misdirection: Pretending to prove "A, therefore B", when actually proving "B, therefore A". May be extended into Proof by Convergent Irrelevancies.
Proof by Definition: Defines S in a way that the proof works but avoids establishing that S is non-empty.
Proof by Assertion: Asserting the proof is obvious and moving on.
Proof by Admission of Ignorance: Asserting something must be true but does not know why.
Proof by Non-Existent Reference: Citing to something that cannot be found.
Proof by Example: Proves for one instance, but neglects to prove for all instances.
Proof by Assignment: Leaving the proof as an exercise for the reader.
Delayed Lemma: Announces that proof will be provided later, then moves on. If the proof is never provided it becomes Proof by Infinite Neglect.
Proof by Circular Cross-Reference: Creates a chain of reasoning that may be an infinite loop.
Proof by Osmosis: The proposition is never stated, and no hint of its proof is given, but by the end of the discussion it is tacitly assumed to be known.
Proof by Aesthetics: "This result is too beautiful to be false".
Proof by Oral Tradition: Asserting there is a proof, perhaps reported by another, but not having it available.

Acknowledgment: Many of the above were suggested by Stephen Downes, now found on this web page.

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