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Logical Fallacies

Contents

  1. 1 What is a Logical Fallacy?
  2. 2 Formal Logical Fallacies  
    1. 2.1 Non sequitur
    2. 2.2 Fallacies of Conditional Syllogisms
      1. 2.2.1 Affirming the Consequent
      2. 2.2.2 Denying the Antecedent
    3. 2.3 Fallacies of Categorical Syllogisms
      1. 2.3.1 Illicit Major 
      2. 2.3.2 Undistributed Middle  
      3. 2.3.3 Fallacy of Exclusive Premises
  3. 3 Informal Logical Fallacies  
    1. 3.1 Ad Populum (or "Appeal to Popularity") 
    2. 3.2 Ad Populum Bandwagoning 
    3. 3.3 Ad Populum Snobbery 
    4. 3.4 Alternate Description 
    5. 3.5 Appeal to Authority
    6. 3.6 Appeal to Complexity
    7. 3.7 Appeals to Emotion
      1. 3.7.1 Appeal to Pity 
      2. 3.7.2 Appeal to Spite 
      3. 3.7.3 Appeal to Pride 
      4. 3.7.4 Appeal to Shame 
      5. 3.7.5 Appeal to Victimization
      6. 3.7.6 The arguer claims priviliged knowledge of a questionable entity by claiming to be a victim of it (and thereby shielding himself from criticism).
    8. 3.8 Appeal to Force
    9. 3.9 Appeal to Quantum Physics
    10. 3.10 Argument from Antiquity (also Appeal to Tradition)
    11. 3.11 Argument by Artifice 
    12. 3.12 Argument from Final Consequence
    13. 3.13 Argument from Ignorance  (Ad ignormantiam)
    14. 3.14 Argument From Personal Incredulity
    15. 3.15 Bad Reasons Fallacy
    16. 3.16 Begging the Question  
      1. 3.16.1 Begging the Question by Circular Reasoning  
      2. 3.16.2 Begging the Question by Unstated Major Premise
    17. 3.17 Black Swan Fallacy 
    18. 3.18 Burden of Proof 
    19. 3.19 Composition/ Division
      1. 3.19.1 Composition Fallacy 
      2. 3.19.2 Division Fallacy 
    20. 3.20 Confirmation Bias 
    21. 3.21 Confusing Correlation, Coincidence and Causation (False Cause)
      1. 3.21.1 "Cum Hoc Ergo Propter Hoc" 
      2. 3.21.2 Post Hoc Fallacy ("Post Hoc Ergo Propter Hoc")
    22. 3.22 Conjunction Fallacy
    23. 3.23 Equivocation 
    24. 3.24 Exaggerated Conflict
    25. 3.25 Fallacy Fallacy
    26. 3.26 False Analogy
    27. 3.27 False Continuum 
    28. 3.28 False Dichotomy 
    29. 3.29 False Premise
    30. 3.30 Gambler's Fallacy 
    31. 3.31 "Genetic" Fallacies
      1. 3.31.1   The Genetic Fallacy
      2. 3.31.2   Ad Hominem
      3. 3.31.3   Ad Hominem Abusive
      4. 3.31.4   Ad Hominem Association 
      5. 3.31.5   Ad Hominem Circumstantial 
      6. 3.31.6   Ad Hominem Tu Quoque ('You Too')
      7. 3.31.7   Poisoning the Well
    32. 3.32 Gish Gallop
    33. 3.33 Hasty Generalization
    34. 3.34 Loaded Question 
    35. 3.35 Misleading Vividness
    36. 3.36 Moving the Goalpost
    37. 3.37 Nirvana Fallacy
    38. 3.38 "No True Scotsman" 
    39. 3.39 Proof by Lack of Evidence
    40. 3.40 Red Herring 
    41. 3.41 Regressive Fallacy
    42. 3.42 Sanctimony 
    43. 3.43 Self-sealing Fallacy 
    44. 3.44 Slippery Slope Fallacy
    45. 3.45 Special Pleading
    46. 3.46 Straw Man Fallacy
    47. 3.47 Sunk Cost Fallacy
    48. 3.48 Toupee Fallacy
    49. 3.49 Texas Sharpshooter Fallacy
    50. 3.50 Weasel Words 
  4. 4 Conclusion
  5. 5 References and Links
What is a Logical Fallacy?


A logical fallacy is a mistake in reasoning. In deductive logic (and hence in deductive arguments), fallacies are errors in the structure of the argument such that the conclusion does not necessarily follow from the premises. In inductive logic, fallacies are unjustified warrants that the arguer tries to use to support an inference between evidence and a claim. (see Argumentation and Logic).  

Fallacies in deductive arguments are called "formal" logical fallacies. Fallacies in inductive arguments are called "informal" logical fallacies.



Formal Logical Fallacies  

These are errors in an argument's form. They violate the rules of Conditional and Categorical Syllogisms (see Argumentation and Logic).

Non sequitur

In non sequitur fallacies, the conclusion does not follow from the premises. 
The premises and the conclusion may be true, but the conclusion does not follow from the premises.

Students read books.
Books cost money.
Therefore, students have credit cards.


Fallacies of Conditional Syllogisms

Affirming the Consequent

If A is present, then B is present.
B is present.
Therefore, A is present.

False, as A does not account for all of B.

                                                                            
If acupuncture works, 
then it would seem to work.
It seems to work.
Therefore, acupuncture works.



If A, then B
Not A
Therefore, not B

False, as A does not account for all of B.


If pharmaceutical companies were always honest, 
then we could trust drug X.
Pharmaceutical companies are not always honest,
Therefore, we cannot trust drug X.




Fallacies of Categorical Syllogisms

Illicit Major 

The major term is the most inclusive and is the predicate of the conclusion (B). 
It is not distributed over the minor term (C), which is the subject of the conclusion..


All A's are B's
No A's are C's
Therefore, No C's are B's

                                                        
All cars have wheels.
No cars are bicycles.
Therefore, no bicycles have wheels.

 
 
 
The minor term (B) is not distributed over all of the middle or the major.

     
 
All A's are B's
All A's are C's
Therefore, all B's are C's

                                               
All people are mammals.
People are primates.
Therefore, all mammals are primates.
 
 
 

Undistributed Middle  

The middle term in a syllogism is not connected to both of the premises.

 

She's a Witch!

 
All X's are Y's
Z's are Y's
Therefore, all X's are Z's.

A person has 2 legs.
A bird has 2 legs.
Therefore, people are birds.

 
Another great example of the Fallacy of the Undistributed Middle can be seen in the "She's a Witch" scene
(from Monty Python and the Holy Grail.)









Fallacy of Exclusive Premises

All of the major premises are negative. No conclusion can be made.  You need at least one positive premise.
 

A is not B
B is not C
Therefore, A is not C
 
Dogs are not fish.
Fish are not mammals.
Therefore, dogs are not mammals.


 
 

Informal Logical Fallacies  


In a debate, these are misleading errors in reasoning that seem to support the conclusion, but actually are irrelevant or false.  They are false warrants. 
 

Ad Populum (or "Appeal to Popularity") 

An attempt to assign value to something based on how others seem to value it.
 

Ad Populum Bandwagoning 

- An argument that states that something is valuable because many people seem to want it.
 
eg. "This stock must be a great investment because so many people are buying it."
 

Ad Populum Snobbery 

- An argument that states that something must be valuable because it is used only by an exclusive group.
 
eg. "You shouldn't buy Budweiser. Classy people drink imports."
 
  



Alternate Description 

(Similar to the Straw Man Fallacy) One arguer twists the other's argument to sound unappealing. This is done usually by ignoring the main point of the other's argument.
 
eg. "My political opponent wants to use your tax money to give it to people who don't contribute to society! Don't vote for him!" 
 
eg. "My political opponent wants to let the rich keep desperately needed money out of the poorest communities! Don't vote for her!"
 
 

Appeal to Authority

I am Arthur, King of the Britains!

The arguer tries inflate the worth of his argument by associating it with a well known authority who is not an authority on the subject at hand. The arguer may also try to use his/her own authority to persuade listeners.
 
eg. "Jim Carrey thinks that vaccines are causing more harm than good. I won't let my child be vaccinated even though our pediatrician recommends it."
 
See Monty Python and The Holy Grail's "I am Arthur, King of the Britains" scene.
 
 


Appeal to Complexity

The arguer points out the if an idea is too complex for the listeners to understand, then it must be false.

eg. "The human eye is too complex to have evolved from simpler structures." 

The arguer tries to invoke emotions to support the conclusion that really are irrelevant to the argument at hand.
 

Appeal to Pity 

The arguer tries to sway opinion in a positive way by mentioning sad or difficult circumstances that are irrelevant to the issue.
 
eg. "Stan really should get a raise. After all, his wife just had a baby and he still has student loans to pay off."

 

Appeal to Spite 

The arguer tries to sway opinion in a negative way by mentioning undesirable things about the subject that are irrelevant to the issue.
 
eg. "Stan should be fired. He yells at his kids and cheats on his wife!"
 

Appeal to Pride 

The arguer tries to sway opinion by invoking one's sense of pride in a way that is really irrelevant to the argument.
 
eg. "We can do it! After all, we are Americans!"
 
(See also Sanctimony)
 

Appeal to Shame 

The arguer invokes irrelevant shame to sway opinion. 
 
eg. "You are wrong for dropping out of college. And you call yourself my son!"

Appeal to Victimization

The arguer claims priviliged knowledge of a questionable entity by claiming to be a victim of it (and thereby shielding himself from criticism).

eg. "Morgellan's disease is real. I have been suffering from it for years and that's all the science I need!"
 



 

Appeal to Force

This is really just a threat. The arguer tries to get others to adopt his/her point of view or else the arguer will cause them harm.
 
eg. "You'd better start liking the Jonas Brothers or I will tell your parents that you skipped school last week!"




Appeal to Quantum Physics

Quantum Mechanics is used as an explanation for mystical and 'New Age' claims. As most people do not understand quantum mechanics, listeners will be impressed with an argument that uses it as an explanation. Many mistakenly associate the term 'quantum physics' with the science of a bizarre, observer-dependent reality in which anything can happen. It is frequently invoked by gurus like Deepak Chopra and 'Energy Medicine' practitioners.

"Quantum healing is healing the bodymind from a quantum level. That means from a level which is not manifest at a sensory level. Our bodies ultimately are fields of information, intelligence and energy. Quantum healing involves a shift in the fields of energy information, so as to bring about a correction in an idea that has gone wrong. So quantum healing involves healing one mode of consciousness, mind, to bring about changes in another mode of consciousness, body." --Deepak Chopra





Argument from Antiquity (also Appeal to Tradition)

This form of argument tries to pursued the listener that an idea must be true because it has been believed or practiced for a long time.
Of course, an ideas logical worth should have nothing to do with how long people have held it. 

eg. "Slavery is not immoral. It has been practiced for thousands of years. Our culture was built on slavery!"




Argument by Artifice 

The arguer starts with a pre-conceived conclusion and then constructs a contrived, often convoluted, disingenuous argument to support the conclusion.  The arguer's actual motives for the position are not given as part of the argument. 

This process usually includes many logical fallacies and falsehoods in the construction of the argument. The argument is often used to justify policies by institutions or in legal cases.  This is a telling sign of pseudoscience.
 


 

Argument from Final Consequence

This states that the argument must be wrong if the conclusion is very unpleasant. The merits of the argument are not considered.  Usually uses Wishful Thinking.
 
eg. "Our new blood pressure medication has got to be the best one on the market. Otherwise, our competitors will beat us in sales again this year."
 
(see also the "Sunk Cost Fallacy")
 
eg. "Then it will clarify Engel’s statement: men make their history on the basis of real, prior, conditions (among which we would include acquired characteristics, distortions imposed by the mode of work and of life, alienation, etc.), but it is the men who make it and not the prior conditions. Otherwise men would be merely the vehicles of inhuman forces which through them would govern the social world." (SartreCritique, p. 87.)
 



Argument from Ignorance  (Ad ignormantiam)

States that because something is unknown, it cannot be true. Alternatively, if something is not known to be false, it must be true. This fallacy would have you think that the absence of evidence is evidence of absence.
 
This often is used with the False Dichotomy to state that lack of evidence in one position proves the opposing position.
 
eg. "There can't be life on other planets. We have never seen any evidence of aliens!"
 


Argument From Personal Incredulity

The arguer tries to get the listener to think that something cannot be true because it is unbelievable (to the arguer).
 
eg. "It is obvious that the Sun goes around the Earth. Copernicus is wrong. His ideas about the Earth going around the sun are too far-fetched to be true. I don't believe that."
 



 
(Proof by Intimidation, Shotgun Argument, Gish Gallop)

The arguer produces an overwhelming array of statements and/or technical jargon in a relatively short period of time.  The opponent is unable to address them all or even understand them.  Observers will likely be impressed, but have no way of checking the validity of the claims.
 
"If you can't dazzle them with brains, baffle them with bull". (attributed to W.C. Fields)






Bad Reasons Fallacy

As opposed to False Premise, this fallacy holds that the conclusions of an argument must be false if the premise(s) are false. While this may be true sometimes, it is not necessarily true.
 
eg. "Phil thinks that the sun goes around the Earth in a circular path. Therefore, he says, the Earth must be round.  We all know that the sun doesn't go around the Earth. Therefore, the Earth isn't round."




Begging the Question  

Begging the Question by Circular Reasoning  

The conclusion is really just restating one or more of the premises in a different way. In the end, nothing is actually proven or learned. It is really just the Law of Identity
 
A = B
Therefore, A = B 
 
If A then B
Therefore A

Or even...

A....
Therefore A.

 
Note that these are perfectly sound and valid, yet prove no point.
 
eg. "That book was really good because I enjoyed it so much."
 
eg. "I believe that you will succeed because I have faith in you."
 
This may come in the form of a Tautology.


Begging the question fallacies can allow for unwarranted attribution of authority. For instance, "Fortune cookies reveal truth because it said so in a fortune cookie". 


Begging the Question by Unstated Major Premise

The argument is presented without stating one of its major premises.  It is assumed that this premise is understood by the listener and that the listener agrees with it. This may not be the case.
 
This can be a straightforward formal fallacy by itself or can take the form of a False Premise Fallacy (see above) if the unstated premise is false. 
 
It can have the flavor of an informal fallacy if the the unstated premise is such that, if stated, would make the argument sound ridiculous.  The arguer intentionally does not state the premise.

This actually moves an argument past the basic stasis point of conjecture without establishing conjecture in the first place.
 
eg). "People who are abducted by aliens are left emotionally traumatised by the event. We should therefore set up clinics to care for these people."
 
The unstated major premise here is that aliens are actually abducting people. If the arguer actually stated this, he/she runs the risk of sounding ridiculous. The arguer avoids this by not stating this premise.  

Used in "Loaded Questions".

 


Black Swan Fallacy 

The arguer concludes that a concept does not exist because it has not been observed.  This comes from the observation that since most swans are white, one may never see a black swan and therefore conclude that 'all swans are white'.  However, there are black swans in the world that the observer is unaware of.
 
This exemplifies Popper's ideas about falsification.  A claim is not scientific unless it is potentially falsifiable. One cannot prove a claim to be true by demonstrating large numbers of positive examples, but one can disprove a claim by finding one or more negative examples.
 
 


Burden of Proof 

Instead of providing evidence to support a claim, the arguer implies that it is true because his/her opponent has not proved it to be false.
 
Alternatively, one could argue that because the opponent hasn't proven a statement to be false, then it must be true.
 
Actually, it is accepted that the burden of proof for an unusual claim lies with the person who is making the claim. "Extraordinary claims require extraordinary evidence" (Carl Sagan)

eg. "The government does have you believe that aliens have not been visiting us over the years.  I tell you that the aliens are here. The government has not provided evidence to the contrary despite our allegations!"




Composition/ Division

Composition Fallacy 

The composition Fallacy is committed when one assumes that a quality of a thing can be determined by the quality of its individual parts.
 
eg. "The Detroit Lions must be a great football team.  It has many first round draft picks." 

Division Fallacy 

The division fallacy is committed when one assumes that a quality of a thing's individual parts can be determined by the quality of the whole.
 
eg. "The players on the Detroit Lions must be pretty bad because the team loses so many games." 

 


Confirmation Bias 

(Actually this is a Cognitive Bias but can take the form of a Logical Fallacy)

We tend to remember the events that confirm our previously held ideas, but minimize or ignore all of the events that contradict our convictions.
 
"Remembering the hits and forgetting the misses"; places significance on coincidences.
 
eg. "I truly think that I am psychic. Whenever I dream about a person, I tend to run into them the next day!" (except for all the times that you don't, which is most of the time).
 
 



Confusing Correlation, Coincidence and Causation (False Cause)

"Cum Hoc Ergo Propter Hoc" 

When two things seem to happen in correlation with each other, many will mistakenly think that one thing caused the other when no such causal relationship has been established.

eg. "Many people who have strokes are on blood pressure medications.  Those blood pressure pills must be causing strokes."

Post Hoc Fallacy ("Post Hoc Ergo Propter Hoc")

 
A precedes B, therefore A caused B
 
eg. "My kids both got their Meningitis shot when they were 16. Right after that, they both got speeding tickets.  That shot must cause people to drive recklessly!"





Conjunction Fallacy

This occurs when one assigns higher likelihood to an option that contains a basic assumption plus additional assumptions over an option that contains only the basic assumption alone. This happens when the additional assumptions seem to fit the subject more specifically, often because of stereotypes. It is best understood with examples.

eg. Dr. T is seeing a patient named Curt in his clinic. Curt is a 20 year old male with long hair and tattoos. He wears a tee shirt with an anti-war slogan and has a peace sign pendant around his neck.

What is more likely? Curt is a college student, or, Curt is a college student who is an anti-war activist?

Studies suggest that most people would choose the second option because it seems to fit the description. However, since the second option contains an additional assumption over the first, it cannot be more likely.

eg. What is more likely? 
       A or A+B

Most would have no trouble seeing that A+B has the additional assumption (B), therefore cannot be more likely than A alone. However, if A+B seems to fit an image better than just A.

It can be seen when conspiracy theorists become more convinced of the conspiracy as more details are added (eg. JFK was assassinated and the CIA was behind the assassination).

Another great example is found here regarding the misguided claim that the HPV vaccine leads to female infertility:

"The idea that Gardasil causes infertility probably arises from two misguided notions: (1) that Gardasil gives girls “permission” to be “promiscuous”; and (2) that promiscuity has sexual and reproductive consequences, in this case infertility."

 
 



Equivocation 

The arguer covertly uses an alternate definition of a word that is key to the discussion.

Arguer A: "The Theory of Evolution should be taught in schools."
Arguer B: "No it shouldn't because, by your own admission, it is only a theory!"

Here, A is using theory in the scientific sense to mean the best explanation for a phenomenon based on the evidence as it is currently understood.
B is using theory in the common usage to mean 'a hunch'. 

(Note- Amphiboly is similar and refers to phrases with alternate meanings rather than words).
 
 


 

Exaggerated Conflict

The arguer seizes upon any disagreement among experts over the details of a concept as evidence against the concept itself.
 
eg. "High cholesterol probably isn't bad for you. Doctors can't even agree on how low it should be or which of the cholesterols is the most important one." 
   
  


Fallacy Fallacy

This is a tricky one that skeptics have to be wary of.  We may be tempted to claim that the conclusion of an argument is wrong because the arguer used a logical fallacy in his or her reasoning. 
Just because a fallacy was used does not mean that the conclusion is necessarily incorrect.

eg. "Fred claimed that his car gets the best gas mileage because his favorite basketball player endorsed it. He must be wrong. Doesn't he know that's an argument from authority?"
(Fred did commit an argument from authority and is wrong to think that the car was the best just because the basketball player said so. But that does not mean that his conclusion is necessarily wrong.)




False Analogy

This is committed when the arguer tries to compare 2 things that seem alike in one way, but really are not alike in the way that is relevant to the argument: comparing apples to oranges.
 
eg. "Mike is a lot like Bill, because they both like country music. Mike owes me money. I wouldn't trust Bill if I were you." 





False Continuum 

The arguer tries to show that 2 things are really the same because they are tied together by a continuum and that one cannot clearly state where one extreme of the continuum ends and the other begins. It denies that the extremes of a continuum are actually different.


eg. "A grain of sand is not a heap of sand, and neither are two or three grains of sand...therefore there is no fundamental difference between a grain and a heap." (Fallacy of the Heap).

eg. "One hair on the chin does not make a beard...etc". (Fallacy of the Beard)








False Dichotomy 

The arguer gives the impression that there are only 2 extreme positions that are possible. This does not allow for moderate, middle grounds or grey areas. Can be related to the Bad Reasons Fallacy. It assumes that the subject is part of a Tautology ("A or not A")
 
eg. "You're either with us, or against us!"
 
eg. "People are either Republicans or Democrats"
 
Note - this fallacy is often used to discredit fairly sound theories on the basis of anomalies ("anomaly hunting")





False Premise

An argument can be sound or strong, yet may be completely false if at least one of the premises is not true. False premises cause the arguments to be not valid or cogent (although they may be sound or strong)
 
eg. "Tooth Fairy Science" (Harriet Hall, MD, aka "The Skepdoc")
 
 "You could measure how much money the Tooth Fairy leaves under the pillow, whether she leaves more cash for the first or last tooth, whether the payoff is greater if you leave the tooth in a plastic baggie versus wrapped in Kleenex. You can get all kinds of good data that is reproducible and statistically significant. Yes, you have learned something. But you haven’t learned what you think you’ve learned, because you haven’t bothered to establish whether the Tooth Fairy really exists."
  
 


Gambler's Fallacy 

The mistaken belief that a random event must be due to happen soon if it has not happened in an unusually long time.
 
eg. "My team is due to win tonight.  They haven't won a game in over 4 weeks.

eg. "I haven't hit a jackpot on this slot machine after a whole hour of playing. I'll keep playing because a jackpot is really overdue."
 
This is related to the "Hot Hand Fallacy" and the "Sports Illustrated Cover Jinx".
 
A basketball player who is making a greater number of baskets than average in a particular game is said to have a "hot hand". However, when flipping a coin numerous times, one can occasionally expect a string of "tails" purely by chance. Upon continued flipping, the rate of "tails" will likely regress to the mean.
 
Such a player may then get more recognition that he deserves and make the cover of "Sports Illustrated". At this point, his shooting regresses to the mean. It is then said that being on the cover "jinxed" him.
 




"Genetic" Fallacies

These fallacies are attacks on the origin of the premises instead of addressing the merits of the argument itself.  

  The Genetic Fallacy

This fallacy can take two forms. 

First, it is fallacious to argue that a position is wrong just because the origin of the premise is unknown. 
eg. "You shouldn't take that proverb seriously, because you don't even know who said it first."

Some statements are commonly used today that, at one time, had different meanings than they do in modern usage. For instance, one may program a digital recorder to "tape" a favorite television show. It would be fallacious to attack this statement as untrue because "tape" is not involved in digital recordings. This version of the Genetic Fallacy is sometimes called the Entymological Fallacy

  Ad Hominem

An attack on the person presenting the argument, rather than on the merits of the argument.

  Ad Hominem Abusive

This is an insult that is given instead of a reason.
     
eg. "You are wrong because you are a moron!"

Note - "You are a moron!" is NOT (by itself) a logical fallacy, it is simply an insult. 
 

  Ad Hominem Association 

This is an attempt to discredit the arguer by linking him or her to something or someone that is thought of in a negative way.
 
eg. "We shouldn't take him seriously. His company used to do business with organized crime."
 

  Ad Hominem Circumstantial 

This is an attack on the circumstances of the arguer. May imply ulterior motives or conflict of interests.
    
 eg. "Of course the Senator wants more laws. He is a politician. Making more laws is what keeps politicians in business!"
 

  Ad Hominem Tu Quoque ('You Too')

The arguer is accused of the practice that he/she is arguing against. May imply hypocrisy.
    
eg. "Bob said that I should obey the speed limit, but I see him driving fast all the time!"

  Poisoning the Well

This is committed when one arguer attempts to bias the listener against his/her opponent, sometimes even before the argument begins. May be thought of as a form of Ad Hominem.
 
eg. "My opponent, a known socialist and outspoken opponent of free enterprise, would have you believe that his economic plan is better than mine. But don't be deceived."
 
 




Gish Gallop

Also known as Argument Verbosum and "spreading", this term was coined by Eugenie Scott. It is named after Duane Gish, a debater famous for "machine gunning" statements, questions and claims rapidly to overwhelm his opponent. The opponent cannot possibly keep up or refute each claim. The talking points in a "Gish Gallop" may be false, misleading or fallacious, however the argument sounds convincing because the opponent is unable to address them all.

You Have to Be a Super Hero to Answer the Gish Gallop


The opponent may begin to refute the initial talking points, but is then soon drowned in a flood of other claims in rapid succession. The proponent "wins" the debate by overwhelming the opponent rather than presenting a reasonable argument. The Gish Gallop traps the opponent into wasting time trying to debunk the onslaught of ad hominems, half-truths, straw man claims and outright falsehoods, rather than making his/her own points. 

This is a common technique used by pseudo-scientists when debating their real-science counterparts on T.V. "news" programs. 

See "You Have to Be a Super Hero to Answer the Gish Gallop".








Hasty Generalization

The arguer attributes a property to an entire group based only on observing that property in an individual.
 
eg. "People from Jabudasberg are nuts. My old roommate hailed from there and he did some pretty crazy things."
 
  


Loaded Question 

A question posed that implies an unstated major premise such that any answer will trap the answerer into appearing to agree with the unstated premise. (See Begging the Question above)
 
eg. - "Do you still cheat on your wife?"  This implies the premise that you have cheated on your wife.
 
 


Misleading Vividness

This fallacy may be why anecdotal evidence can seem so compelling. When the arguer presents an anecdote that is vivid and emotionally compelling, the listener may assign a higher likelihood that the anecdote represents a typical example that can be generalized to most cases.

eg. - I will never get a vaccine. My friend Bob got a flu shot and became so sick that his whole body swelled up and he puked for 3 days straight. He stayed sick for an entire year and felt like a truck ran over him. 





Moving the Goalpost

When criteria are met that falsify the arguer's position, the arguer changes the criteria and claims that his/her position is still valid. 
 
eg. "OK, so you don't find any association between the mercury preservative in vaccines, but what about the aluminum?"

Also occurs when the arguer covertly changes the stasis point of an argument.









Nirvana Fallacy

When arguing against an action or policy, this fallacy is committed if the arguer declares the action to be useless if it does not lead to ideal conditions. It is related to the false dichotomy in that it implies that if the action does not lead to perfection, then it is useless. It does not recognize that simple improvement is worthwhile.

Essentially, if it isn't perfect, then it is useless.

eg. "The Flu vaccine only works 65% of the time. Don't waste your time getting this."




"No True Scotsman

If the premise of the argument is falsified with a counter example, rather than changing the conclusion, the arguer changes the definition of a major premise to make both the premise and the conclusion true.
  
Typically, the arguer makes a sweeping generalization about a an entire group. This is usually done by implying that the group is bound and defined by the arbitrary quality. 
If an exception to this generalization is pointed out, the arguer dismisses the exception as not truly belonging to the group in the first place.

May be a form of "Special Pleading" and "Self-sealing" argument. 

The examples for this usually involves the Scottish dish called Haggis.

Peter:   No Scotsman would ever put ketchup on Haggis.
David:  Oh? Monty puts ketchup on Haggis.
Peter:   Hmm. Well...no true Scotsman puts ketchup on Haggis. Monty is no true Scotsman.

or

Arguer:      An American would never surrender to an enemy.
Opponent:  Really? In World War II, many of our soldiers surrendered.
Arguer:       Well, they weren't true Americans!   
 
 


Proof by Lack of Evidence

This fallacy is used by conspiracy theorists. Powerful conspiratorial forces will cover their tracks well, so that no evidence of the conspiracy can be expected.

eg. "Of course all of the so-called 'experts' claim that vaccines are safe. They have to say that because they are being paid off or blackmailed by the pharmaceutical industry."

The following is an actual entry by a 9/11 conspiracy theorist on YouTube. He makes his case for a government conspiracy by reviewing the evidence against a government conspiracy and then claiming that it all could have been forged:

"A quick summary of things I would need to convince me 9/11 was not an Inside Job:
1. A Single Piece of evidence to prove this was Al Qaeda which couldn't possibly have been manufactured by the CIA. All the evidence appears manufactured. Show me something substantial which couldn't possibly have been manufactured.
2. The original Black Boxes and NTSB data which matches reality.
3. An Image or video proving a Boeing 757 really hit the Pentagon."






Red Herring 

The opponent deceptively changes the argument to a different topic, i.e. she changes the subject.

Red Herring

 
 
This can be considered a general heading that includes Genetic fallacies and Appeals to Emotion.
 
This comes from the practice of using a smelly fish (red herring) across the path of hounds in a fox hunt to throw off the scent and send the hounds in the wrong direction. 
 
 
 





Regressive Fallacy

Regression to the mean is observed in complex systems. The average conditions of a system represent the steady state. When the conditions of a system fluctuate above or below the mean, it is likely that conditions will return soon return to the steady state. We see this in weather patterns and stock markets.  Storms tend to be followed by calm. Bull markets tend to be followed by corrections. We also see it in health. Periods of illness tend to be followed by return to health.

The arguer commits the Regressive Fallacy when she mistakenly attributes normal fluctuations in a system to causative effects of an intervention. In medicine, natural fluctuations and progression of illnesses lead us to think that a pill is curing a cold or that touch therapy is curing back pain. As symptoms naturally peak and then decline, any intervention started at the peak will be credited for the decline. In randomized controlled trials, a placebo is used as a null surrogate for the treatment to eliminate any direct treatment effects from the equation. If the treatment has no inherent effects, substituting the placebo will leave only the background fluctuations and biases to account for the perceived effect of improvement (or worsening).  




Sanctimony 

The arguer implies that his/her position has moral superiority over the opponent's position. It claims the moral high-ground and implies an "I'm better than you" attitude without considering the opponent's position objectively.
 
eg. "As a decent, law-abiding citizen of this great nation, I urge you to vote 'Yes' on Proposal Z!"
 
eg. "I appear before you today as someone who cares about health. I exercise every day, I eat only organic, plant-based products and never smoke. I doubt that you could say the same for my opponent." 
 
This is related to Appeal to Pride and Poisoning the Well.




Self-sealing Fallacy 

You create a claim that can be declared valid no matter what the outcome (unfalsifiable). "Tails I win, heads you lose".

eg. "If you want your team to win, then you have to have spirit!"
(If the team wins, then you must have had spirit. If the team doesn't win, then you must not have had enough spirit.)

Similar to the No True Scotsman Fallacy
 
 



Slippery Slope Fallacy

YouTube Video

The arguer tries to convince others that one action will lead to a series of events that will eventually lead to an ultimate, usually unwanted, consequence.  This is fallacious if it is unlikely that each intermediate step will necessarily follow the preceding one.
 
eg. "We can't allow kids to wear tee shirts to school. This casual kind of dress will lead to lazier attitudes about school.  Lazy attitudes will lead to poor grades. When kids get poor grades, their self-esteem will go down.  This will cause them to do drugs and commit crimes. I don't know about you, but I want our kids to go to college, not prison!"

A great example of the Slippery Slope Fallacy can be seen in the Trial Scene from National Lampoon's Animal House.
 
 
 
 




Special Pleading

The arguer attempts to explain a discrepancy in his/her argument by assigning special properties to his/her position that immunizes it from criticism. Special Pleading may render a claim unfalsifiable.
 
The fallacy of Special Pleading occurs when someone argues that a case is an exception to a rule based upon an irrelevant characteristic that does not define an exception.
 
Special Pleading also may occur when the arguer implies that opponents of his/her point of view cannot possibly understand it because they lack the capacity or skills needed to comprehend it. 
 
eg. "Of course the psychic failed the test. Such powers do not work when subjected to the negative vibrations of skeptics and scientific testing."
 
eg. "The officer should not have given me a ticket. My wife is a cop, for goodness sake!"
 
eg. "It is not surprising that you reject my proposal.  You were not raised here and cannot possibly understand the issue." 
 
 



Straw Man Fallacy

YouTube Video

The arguer creates a misrepresentation of the opposing argument such that listeners would find obvious fault with it. This allows the arguer to easily knock it down. Named for a dummy filled with straw that cannot defend itself, such as used in bayonet training.
 
eg. "Doctors don't want you to be healthy. They are paid by Big Pharma to give you pills that keep you sick. They only are interested in treating symptoms and do not want to cure the causes of disease. This way, they make you dependant on them and they make more money. Don't go to doctors. Buy my 'Miracle Cures' book! Doctors don't want you to know about it!"   
(paraphrased from an actual website)

Another example of the Straw Man Fallacy can be seen in Rep. Virginia Fox's address to Congress when discussing how health-care reform will lead to death panels for seniors.

 
 
 






Sunk Cost Fallacy

One tends to hold onto an idea (even if it has been falsified) because he/she has invested a lot of time, money and/or emotional energy into the prospect.  Knowledge of one's sunk cost leads one to be overly optimistic about the prospects of one's success.
 
eg. "I'm not giving up on my perpetual energy machine. I have been working for 10 years on it and invested my life's savings. It has to work!"
 
eg. "I've been investing in stock X every 6 months. It has gone down every quarter for the last 2 years. I'm in too deep to get out now. I'm going to keep buying more. Eventually, it has to go up!" (see also "Gambler's Fallacy") 
 
  

Toupee Fallacy

The arguer claims that they can always recognize when something is present.  This is likely a fallacy because the arguer is not aware of all of the times that he/she did not recognize it.
 
(This fallacy is generally attributed to Rebecca Watson. It is not usually included in lists of Logical Fallacies)
 
"I can always spot a toupee".

"I always know when someone is lying to me".
 


 




Texas Sharpshooter Fallacy

Texas Sharpshooter Fallacy

This is committed when one tries to attribute significance or meaning to random events after the events have already happened. This is usually done to support some pre-existing claim.
 
This happens when studies are done that have no specific, predicted
results. A random clumping of data may be highlighted as being significant, especially if it seems to confirm the hypothesis.

This leads to false conclusions about causation when data clusters by random chance around a given point. Since this is random, repeated trials show that the data is no more likely to fall near this point than any other random point.
  
eg. All of Nostradamus's supposed "predictions".
 
eg. Many of the litany of 'side-effects' listed on pharmacy print-outs that likely resulted from a normal distribution of random events in the study population.
 
eg. The Bermuda Triangle Myth  
 

  

Weasel Words 

Empty words attached to statements that seem to give the statement credibility, but in fact are so vague or uninformative that they add no information to the statement. 
 
Derived from the way a weasel sucks the content out of an egg and leaves an empty shell that has the appearance of an intact egg.
 
eg. "It is said that...",  "In my experience...",  "We all know that..." 

eg. (for medical claims) "supports the immune system", "boosts the immune system", "supports health", etc.




Conclusion


These are common fallacies, but the above list is not comprehensive. Skeptical doctors should be familiar with them in order to spot faulty reasoning when assessing claims. Perhaps more importantly, we should learn logical fallacies so that we can recognize and correct them in our own reasoning and arguments.


John Byrne, M.D.
 
 

References and Links


"Nonsense: A Handbook of Logical Fallacies: Robert J. Gula ..." 2009. 

"Argumentation: The Study of Effective ... - The Great Courses." 2010. 

"Taxonomy of the Logical Fallacies - The Fallacy Files." 2004.
<http://www.fallacyfiles.org/taxonomy.html>

"Logical Fallacies." 2005.
<http://www.logicalfallacies.info/>

Theo Clark. "The Skeptic's Field Guide: Fallacy List." 2008. 

"Some New Logical Fallacies - Skeptoid." 2010.
<http://skeptoid.com/episodes/4217>