View Full Version : Guides to Logical Fallacies

Prodigal Son
Tuesday, February 17th, 2004, 06:24 PM

Ahura Mazda
Sunday, March 21st, 2004, 10:38 PM
A better guide to Logical fallacies would be here: http://www.don-lindsay-archive.org/skeptic/arguments.html (http://www.don-lindsay-archive.org/skeptic/arguments.html)

In Chinkanakistan
Monday, March 22nd, 2004, 01:43 AM
Another one:


Thursday, October 13th, 2005, 09:37 PM
Three listings of common logical fallacies:


Thursday, October 13th, 2005, 09:41 PM
Thanks for the links! They'll come in handy!

Monday, September 15th, 2008, 09:29 PM
What is a logical fallacy?

All arguments have the same basic structure: A therefore B. They begin with one or more premises (A), which is a fact or assumption upon which the argument is based. They then apply a logical principle (therefore) to arrive at a conclusion (B). An example of a logical principle is that of equivalence. For example, if you begin with the premises that A=B and B=C, you can apply the logical principle of equivalence to conclude that A=C. A logical fallacy is a false or incorrect logical principle. An argument that is based upon a logical fallacy is therefore not valid. It is important to note that if the logic of an argument is valid then the conclusion must also be valid, which means that if the premises are all true then the conclusion must also be true. Valid logic applied to one or more false premises, however, leads to an invalid argument. Also, if an argument is not valid the conclusion may, by chance, still be true.
Top 20 Logical Fallacies (in alphabetical order)

1. Ad hominem
An ad hominem argument is any that attempts to counter anothers claims or conclusions by attacking the person, rather than addressing the argument itself. True believers will often commit this fallacy by countering the arguments of skeptics by stating that skeptics are closed minded. Skeptics, on the other hand, may fall into the trap of dismissing the claims of UFO believers, for example, by stating that people who believe in UFO's are crazy or stupid.

2. Ad ignorantiam
The argument from ignorance basically states that a specific belief is true because we don't know that it isn't true. Defenders of extrasensory perception, for example, will often overemphasize how much we do not know about the human brain. UFO proponents will often argue that an object sighted in the sky is unknown, and therefore it is an alien spacecraft.

3. Argument from authority
Stating that a claim is true because a person or group of perceived authority says it is true. Often this argument is implied by emphasizing the many years of experience, or the formal degrees held by the individual making a specific claim. It is reasonable to give more credence to the claims of those with the proper background, education, and credentials, or to be suspicious of the claims of someone making authoritative statements in an area for which they cannot demonstrate expertise. But the truth of a claim should ultimately rest on logic and evidence, not the authority of the person promoting it.

4. Argument from final Consequences
Such arguments (also called teleological) are based on a reversal of cause and effect, because they argue that something is caused by the ultimate effect that it has, or purpose that is serves. For example: God must exist, because otherwise life would have no meaning.

5. Argument from Personal Incredulity
I cannot explain or understand this, therefore it cannot be true. Creationists are fond of arguing that they cannot imagine the complexity of life resulting from blind evolution, but that does not mean life did not evolve.

6. Confusing association with causation
This is similar to the post-hoc fallacy in that it assumes cause and effect for two variables simply because they are correlated, although the relationship here is not strictly that of one variable following the other in time. This fallacy is often used to give a statistical correlation a causal interpretation. For example, during the 1990s both religious attendance and illegal drug use have been on the rise. It would be a fallacy to conclude that therefore, religious attendance causes illegal drug use. It is also possible that drug use leads to an increase in religious attendance, or that both drug use and religious attendance are increased by a third variable, such as an increase in societal unrest. It is also possible that both variables are independent of one another, and it is mere coincidence that they are both increasing at the same time. A corollary to this is the invocation of this logical fallacy to argue that an association does not represent causation, rather it is more accurate to say that correlation does not necessarily mean causation, but it can. Also, multiple independent correlations can point reliably to a causation, and is a reasonable line of argument.

7. Confusing currently unexplained with unexplainable
Because we do not currently have an adequate explanation for a phenomenon does not mean that it is forever unexplainable, or that it therefore defies the laws of nature or requires a paranormal explanation. An example of this is the "God of the Gapsâ" strategy of creationists that whatever we cannot currently explain is unexplainable and was therefore an act of god.

8. False Continuum
The idea that because there is no definitive demarcation line between two extremes, that the distinction between the extremes is not real or meaningful: There is a fuzzy line between cults and religion, therefore they are really the same thing.

9. False Dichotomy
Arbitrarily reducing a set of many possibilities to only two. For example, evolution is not possible, therefore we must have been created (assumes these are the only two possibilities). This fallacy can also be used to oversimplify a continuum of variation to two black and white choices. For example, science and pseudoscience are not two discrete entities, but rather the methods and claims of all those who attempt to explain reality fall along a continuum from one extreme to the other.

10. Inconsistency
Applying criteria or rules to one belief, claim, argument, or position but not to others. For example, some consumer advocates argue that we need stronger regulation of prescription drugs to ensure their safety and effectiveness, but at the same time argue that medicinal herbs should be sold with no regulation for either safety or effectiveness.

11. The Moving Goalpost
A method of denial arbitrarily moving the criteria for "proof" or acceptance out of range of whatever evidence currently exists.

12. Non-Sequitur
In Latin this term translates to "doesn't follow". This refers to an argument in which the conclusion does not necessarily follow from the premises. In other words, a logical connection is implied where none exists.

13. Post-hoc ergo propter hoc
This fallacy follows the basic format of: A preceded B, therefore A caused B, and therefore assumes cause and effect for two events just because they are temporally related (the latin translates to "after this, therefore because of this").

14. Reductio ad absurdum
In formal logic, the reductio ad absurdum is a legitimate argument. It follows the form that if the premises are assumed to be true it necessarily leads to an absurd (false) conclusion and therefore one or more premises must be false. The term is now often used to refer to the abuse of this style of argument, by stretching the logic in order to force an absurd conclusion. For example a UFO enthusiast once argued that if I am skeptical about the existence of alien visitors, I must also be skeptical of the existence of the Great Wall of China, since I have not personally seen either. This is a false reductio ad absurdum because he is ignoring evidence other than personal eyewitness evidence, and also logical inference. In short, being skeptical of UFO's does not require rejecting the existence of the Great Wall.

15. Slippery Slope
This logical fallacy is the argument that a position is not consistent or tenable because accepting the position means that the extreme of the position must also be accepted. But moderate positions do not necessarily lead down the slippery slope to the extreme.
16. Straw Man Arguing against a position which you create specifically to be easy to argue against, rather than the position actually held by those who oppose your point of view.

17. Special pleading, or ad-hoc reasoning
This is a subtle fallacy which is often difficult to recognize. In essence, it is the arbitrary introduction of new elements into an argument in order to fix them so that they appear valid. A good example of this is the ad-hoc dismissal of negative test results. For example, one might point out that ESP has never been demonstrated under adequate test conditions, therefore ESP is not a genuine phenomenon. Defenders of ESP have attempted to counter this argument by introducing the arbitrary premise that ESP does not work in the presence of skeptics. This fallacy is often taken to ridiculous extremes, and more and more bizarre ad hoc elements are added to explain experimental failures or logical inconsistencies.

18. Tautology
A tautology is an argument that utilizes circular reasoning, which means that the conclusion is also its own premise. The structure of such arguments is A=B therefore A=B, although the premise and conclusion might be formulated differently so it is not immediately apparent as such. For example, saying that therapeutic touch works because it manipulates the life force is a tautology because the definition of therapeutic touch is the alleged manipulation (without touching) of the life force.

19. Tu quoque
Literally, you too. This is an attempt to justify wrong action because someone else also does it. "My evidence may be invalid, but so is yours."

20. Unstated Major Premise
This fallacy occurs when one makes an argument which assumes a premise which is not explicitly stated. For example, arguing that we should label food products with their cholesterol content because Americans have high cholesterol assumes that: 1) cholesterol in food causes high serum cholesterol; 2) labeling will reduce consumption of cholesterol; and 3) that having a high serum cholesterol is unhealthy. This fallacy is also sometimes called begging the question.

Source (http://www.theskepticsguide.org/logicalfallacies.asp)

Monday, September 15th, 2008, 09:35 PM
Moderators should be required to know this by heart and hand out warnings accordingly.

Wednesday, October 15th, 2008, 05:18 PM
Formal fallacies

Formal fallacies are arguments that are fallacious due to an error in their form or technical structure. All formal fallacies are specific types of non sequiturs.

* Appeal to probability: because something could happen, it is inevitable that it will happen. This is the premise on which Murphy's Law is based.
* Argument from fallacy: if an argument for some conclusion is fallacious, then the conclusion must necessarily be false.
* Bare assertion fallacy: premise in an argument is assumed to be true purely because it says that it is true.
* Base rate fallacy: using weak evidence to make a probability judgment without taking into account known empirical statistics about the probability.
* Conjunction fallacy: assumption that specific conditions are more probable than a single general one.
* Correlative based fallacies

o Denying the correlative: where attempts are made at introducing alternatives where there are none

o Suppressed correlative: where a correlative is redefined so that one alternative is made impossible
* Fallacy of necessity: a degree of unwarranted necessity is placed in the conclusion based on the necessity of one or more of its premises
* False dilemma (false dichotomy): where two alternative statements are held to be the only possible options, when in reality there are several
* If-by-whiskey: An answer that takes side of the questioner's suggestive question
* Ignoratio elenchi (irrelevant conclusion or irrelevant thesis)
* Homunculus fallacy: where a "middle-man" is used for explanation, this usually leads to regressive middle-man explanations without actually explaining the real nature of a function or a process
* Masked man fallacy: the substitution of identical designators in a true statement can lead to a false one
* Naturalistic fallacy: a fallacy that claims that if something is natural, then it is "good" or "right"
* Nirvana fallacy: when solutions to problems are said not to be right because they are not perfect
* Negative Proof fallacy: that, because a premise cannot be proven false, the premise must be true; or that, because a premise cannot be proven true, the premise must be false
* Package-deal fallacy: when two or more things have been linked together by tradition or culture are said to stay that way forever

Propositional fallacies:

* Affirming a disjunct: concluded that one logical disjunction must be false because the other disjunct is true.
* Affirming the consequent: the antecedent in an indicative conditional is claimed to be true because the consequent is true. Has the form if A, then B; B, therefore A
* Denying the antecedent: the consequent in an indicative conditional is claimed to be false because the antecedent is false; if A, then B; not A, therefore not B

Quantificational fallacies:

* Existential fallacy: an argument has two universal premises and a particular conclusion, but the premises do not establish the truth of the conclusion
* Illicit conversion: the invalid conclusion that because a statement is true, the inverse must be as well
* Proof by example: where things are proven by giving an example

Formal syllogistic fallacies

Syllogistic fallacies are logical fallacies that occur in syllogisms.

* Affirmative conclusion from a negative premise
* Fallacy of exclusive premises: a categorical syllogism that is invalid because both of its premises are negative
* Fallacy of four terms: a categorical syllogism has four terms
* Illicit major: a categorical syllogism that is invalid because its major term is undistributed in the major premise but distributed in the conclusion
* Illicit minor: a categorical syllogism that is invalid because its minor term is undistributed in the minor premise but distributed in the conclusion.
* Fallacy of the undistributed middle: the middle term in a categorical syllogism is not distributed
* Categorical syllogism: an argument with a positive conclusion, but one or two negative premises

Informal fallacies

Informal fallacies are arguments that are fallacious for reasons other than structural ("formal") flaws.

* Argument from repetition (argumentum ad nauseam)
* Appeal to ridicule: a specific type of appeal to emotion where an argument is made by presenting the opponent's argument in a way that makes it appear ridiculous
* Argument from ignorance ("appeal to ignorance"): The fallacy of assuming that something is true/false because it has not been proven false/true. For example: "The student has failed to prove that he didn't cheat on the test, therefore he must have cheated on the test."
* Begging the question ("petitio principii"): where the conclusion of an argument is implicitly or explicitly assumed in one of the premises
* Burden of proof
* Circular cause and consequence
* Continuum fallacy (fallacy of the beard)
* Correlation does not imply causation (cum hoc ergo propter hoc)
* Equivocation
* Fallacies of distribution

o Division: where one reasons logically that something true of a thing must also be true of all or some of its parts

o Ecological fallacy
* Fallacy of many questions (complex question, fallacy of presupposition, loaded question, plurium interrogationum)
* Fallacy of the single cause
* Historian's fallacy
* False attribution

o Fallacy of quoting out of context
* False compromise/middle ground
* Gambler's fallacy: the incorrect belief that the likelihood of a random event can be affected by or predicted from other, independent events
* Incomplete comparison
* Inconsistent comparison
* Intentional fallacy
* Loki's Wager
* Moving the goalpost
* No true Scotsman
* Perfect solution fallacy: where an argument assumes that a perfect solution exists and/or that a solution should be rejected because some part of the problem would still exist after it was implemented
* Post hoc ergo propter hoc: also known as false cause, coincidental correlation or correlation not causation.
* Proof by verbosity (argumentum verbosium)
* Psychologist's fallacy
* Regression fallacy
* Reification (hypostatization)
* Retrospective determinism (it happened so it was bound to)
* Special pleading: where a proponent of a position attempts to cite something as an exemption to a generally accepted rule or principle without justifying the exemption
* Suppressed correlative: an argument which tries to redefine a correlative (two mutually exclusive options) so that one alternative encompasses the other, thus making one alternative impossible
* Wrong direction

Faulty generalizations:

* Accident (fallacy): when an exception to the generalization is ignored
* Cherry picking
* Composition: where one infers that something is true of the whole from the fact that it is true of some (or even every) part of the whole
* Dicto simpliciter

o Converse accident (a dicto secundum quid ad dictum simpliciter): when an exception to a generalization is wrongly called for
* False analogy
* Hasty generalization (fallacy of insufficient statistics, fallacy of insufficient sample, fallacy of the lonely fact, leaping to a conclusion, hasty induction, secundum quid)
* Loki's Wager: insistence that because a concept cannot be clearly defined, it cannot be discussed
* Misleading vividness
* Overwhelming exception
* Spotlight fallacy
* Thought-terminating cliché: a commonly used phrase, sometimes passing as folk wisdom, used to quell cognitive dissonance.

Red herring fallacies

A red herring is an argument, given in response to another argument, which does not address the original issue. See also irrelevant conclusion

* Ad hominem: attacking the personal instead of the argument. A form of this is reductio ad Hitlerum.
* Argumentum ad baculum ("appeal to force", "appeal to the stick"): where an argument is made through coercion or threats of force towards an opposing party
* Argumentum ad populum ("appeal to belief", "appeal to the majority", "appeal to the people"): where a proposition is claimed to be true solely because many people believe it to be true
* Association fallacy & Guilt by association
* Appeal to authority: where an assertion is deemed true because of the position or authority of the person asserting it
* Appeal to consequences: a specific type of appeal to emotion where an argument concludes a premise is either true or false based on whether the premise leads to desirable or undesirable consequences for a particular party
* Appeal to emotion: where an argument is made due to the manipulation of emotions, rather than the use of valid reasoning

o Appeal to fear: a specific type of appeal to emotion where an argument is made by increasing fear and prejudice towards the opposing side

o Wishful thinking: a specific type of appeal to emotion where a decision is made according to what might be pleasing to imagine, rather than according to evidence or reason

o Appeal to spite: a specific type of appeal to emotion where an argument is made through exploiting people's bitterness or spite towards an opposing party

o Appeal to flattery: a specific type of appeal to emotion where an argument is made due to the use of flattery to gather support
* Appeal to motive: where a premise is dismissed, by calling into question the motives of its proposer
* Appeal to novelty: where a proposal is claimed to be superior or better solely because it is new or modern
* Appeal to poverty (argumentum ad lazarum)
* Appeal to wealth (argumentum ad crumenam)
* Argument from silence (argumentum ex silentio)
* Appeal to tradition: where a thesis is deemed correct on the basis that it has a long-standing tradition behind it
* Chronological snobbery: where a thesis is deemed incorrect because it was commonly held when something else, clearly false, was also commonly held
* Genetic fallacy
* Judgmental language
* Poisoning the well
* Sentimental fallacy: it would be more pleasant if; therefore it ought to be; therefore it is
* Straw man argument
* Style over substance fallacy
* Texas sharpshooter fallacy
* Two wrongs make a right
* Tu quoque

Conditional or questionable fallacies

* Definist fallacy
* Slippery slope

List of Fallacies (http://en.wikipedia.org/wiki/List_of_fallacies)
Links to all at source.

Saturday, November 15th, 2008, 05:16 PM
In psychology and cognitive science, confirmation bias is a tendency to search for or interpret new information in a way that confirms one's preconceptions and avoids information and interpretations which contradict prior beliefs. It is a type of cognitive bias and represents an error of inductive inference, or as a form of selection bias toward confirmation of the hypothesis under study or disconfirmation of an alternative hypothesis.

Confirmation bias is of interest in the teaching of critical thinking, as the skill is misused if rigorous critical scrutiny is applied only to evidence challenging a preconceived idea but not to evidence supporting it.