Fallacies

 This page discusses and lists popular fallacies encountered in daily life.

What are fallacies?

Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments or irrelevant points, and are often identified because they lack evidence that supports their claim

Some Questions

• Why do we study fallacies?
• People are often illogical, in what situations are understanding fallacies important?
• Should we point out others' fallacies in their arguments?

Formal Fallacies

Affirming a disjunct

This is a fallacy when someone concludes that one disjunct of a logical disjunction must be false because the other disjunct is true; A or B; A, therefore not B.

Affirming the consequent 

This is a formal fallacy of taking a true conditional statement (e.g., "If the lamp were broken, then the room would be dark,") and invalidly inferring its converse ("The room is dark, so the lamp is broken,") even though the converse may not be true. This arises when a consequent ("the room would be dark") has more than one other possible antecedents (for example, "the lamp is not plugged in" or "the lamp is in working order, but is switched off").

Denying the antecedent

This is a fallacy when someone concludes that the consequent in an indicative conditional is false because the antecedent is false; if A, then B; not A, therefore not B.

Base rate fallacy : statistical paradox

See Youtube videos below: 

• STAR TREK Logical Thinking #38 - Base Rate Neglect (Base Rate Fallacy)
• How To Update Your Beliefs Systematically - Bayes’ Theorem
• False positives and false negatives: disease screening - conditional probability - Bayes Theorem
• Bayes theorem, the geometry of changing beliefs

Informal Fallacies

Ad hominem

Ad hominem (Latin for 'to the person'), short for argumentum ad hominem, refers to several types of arguments, some but not all of which are fallacious. Typically this term refers to a rhetorical strategy where the speaker attacks the character, motive, or some other attribute of the person making an argument rather than attacking the substance of the argument itself. This avoids genuine debate by creating a diversion to some irrelevant but often highly charged issue. 

Appeal to probability

Taking something for granted because it would probably be the case (or might possibly be the case).

Argument from fallacy 

(also known as the fallacy fallacy) – the assumption that, if a particular argument for a "conclusion" is fallacious, then the conclusion by itself is false

Begging the question

Another name for this fallacy is Assuming the conclusion.  To 'assume the conclusion' or to 'beg the question' (also called petitio principii) is to attempt to support a claim with a premise that itself restates or presupposes the claim. It is an attempt to prove a proposition while simultaneously taking the proposition for granted. (source: Wikipedia page on "Begging the Question" dated 22/8/21.)

During the Australian same sex marriage debate in 2017, an opponent to same sex marriage argued that same sex marriage was unacceptable as marriage was defined to be a union between a man and a woman.  The premise "marriage was defined to be a union between a man and a woman" assumes the conclusion "same sex marriage was unacceptable".

Equivocation

False dichotomy

Post hoc ergo propter hoc

This is an informal fallacy committed when a person reasons that because one event happened after another event, the first event caused the second. 

Slippery slope

Statistical fallacy

Using numbers in such a manner that – either by intent or through ignorance or carelessness – the conclusions are unjustified or incorrect.  Another term for this fallacy is 'Misuse of Statistics'. 

The claim by PM Scott Morrison in June 2021 on the success of hotel quarantine is an example of Statistical Fallacy as shown in the ABC fact checker article below: https://www.abc.net.au/news/2021-07-15/fact-check-is-hotel-quarantine-99-9-per-cent-successful/100289242 

Politicians routinely quote statistics that shine a good light on their story.  For example, carbon dioxide emission is quoted as a percentage of total global emission (and not emission per capita); while refugee intake is presented as ranking on per capita basis (and not as a percentage of total refugee intake).

For CO2 emission, see: https://ourworldindata.org/co2/country/australia

For refugee intake, see: https://www.refugeecouncil.org.au/2018-global-trends/

Straw man

A straw man is an informal fallacy of having the impression of refuting an argument, whereas the real subject of the argument was not addressed or refuted, but instead replaced with a false one. One who engages in this fallacy is said to be "attacking a straw man".  (source: Wikipedia page on "Straw man" dated 25/8/21.)

For example:

A: Practice X should be banned as it can cause serious harm to people.

B: Banning practice X is an attack on freedom of expression.  Freedom of expression must not be tempered with.  This is the most serious attack on our freedom of expression ever....

B is attacking a straw man since instead of arguing about whether practice X harms people or not, B is arguing about freedom of expression.

Fallacy Lists 

The following lists some websites that provide list of fallacies:

Fallacy and Biases - https://philosophy.hku.hk/think/fallacy/index.php

Fallacy Files -  http://www.fallacyfiles.org/index.html

Information is Beautiful - Rhetological Fallacies

Internet Encyclopedia of Philosophy - Fallacies

Wikipedia - List of Fallacies - https://en.wikipedia.org/wiki/List_of_fallacies 

Youtube playlists:

• Logic Lessons with Mr. Spock 
• Phil-o-note - Informal Fallacies 
• Wifi Philosophy - Critical Thinking: Fallacies
• Wifi Philosophy -  Introduction to Critical Thinking 

Your Bias is - https://yourbias.is/ 

Your Logical Fallacies - https://yourlogicalfallacyis.com/