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FALLACIES

Learn about different types of formal and informal fallacies, such as affirming the consequent and denying the antecedent, to distinguish valid arguments from faulty reasoning. Discover how to identify logical fallacies and strengthen your critical thinking skills.

williamsemily
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FALLACIES

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  1. FALLACIES LUNA HERNÁNDEZ GARCÍA

  2. WHAT IS AN ARGUMENT? • Logic: the science that evaluates arguments. • Argument: a group of statements, a group of which serve (the premises) to support, imply, or provide evidence for another statement (the conclusion). • Premises: set forth the reasons for the conclusions. • We must distinguish between good and bad arguments. A good argument is one in which the premises support the conclusion.

  3. A good argument • Socratesis a man Premise • Allmen are mortal  Premise • Therefore, Socratesis mortal  Conclusion • Thisargumentisvalid and true.

  4. VALIDITY vs TRUTH • Validity: a deductiveargumentiseithervalidorinvalid. • A deductiveargumentisvalidiftheconclusionfolllowsnecessarilyfromthepremises: ifitisnecessarilythe case thatifthepremiseswere to be true, thentheconclusionmust true (whetheritis in fact true ornot). • Ifthereisanypossibilitythatallthepremisescould be true and theconclusion false, thentheargumentisinvalid. • NOTE: Thetruth of thepremisesisnotrequiredforvalidity.

  5. IfSpainwinsthe Soccer World Cup, allmystudentswilldreamaboutlemontrees.  Premise • Spain won theWorld Cup.  Premise • So, allmystudentsdreamtaboutlemontrees.  Conclusion • Thisargumentisvalid and correctbecausethepremisessupporttheconclusion: • P  Q • P • Then, Q • Butthisargumentisnot truebecausethefirstpremiseis false. So theargumentisfalse. Butitisvalid and correctbecauseitsstructureiscorrectand logical.

  6. What is a fallacy? • A fallacy is the use of invalid or faulty reasoning in the construction of an argument. • A fallacious argument may be deceptive by appearing to be better than it really is. • Some fallacies are committed intentionally to manipulate or persuade by deception, carelessness or ignorance.  

  7. Formal fallacies and informal fallacies • A fallacyisanargumentthat uses poorreasoning. • Anargument can be fallaciouswhetherornotitsconclusionis true. • A fallacy can be either formal or informal. • An error thatstemsfrom por logicalformiscalled “formal fallacy” orsimplyaninvalidargument.  In philosophy, wealsocallthesefallacies “logicalfallacies”. • An informal fallacyisan error in reasoningthatdoesnotoriginate in improperlogicalform.  Argumentscommitting informal fallaciesmay be formallyvalidbutstillfallacious.

  8. Formal fallacies and informal fallacies Formal or logical fallacy Informal fallacy A fallacy that requires an analysis of the content of the argument and not just an inspecrion of its form. • A fallacy that may be identified by a mere inspection of the form of the argument.

  9. Formal fallacies and informal fallacies FORMAL FALLACIES INFORMAL FALLACIES Arguments that are fallacious for reasons other than structural (formal) flaws and usually require examination of the argument's content. Informal fallacies can have good form in the argument itself, but there is a defect in the content. These fallacies relate to the unsoundness of the premises. • It is an error in logic that can be seen in the argument’s form. • Formal fallacies have a defect because of the poor form of the argument; so they are a violation of a logical principle. • All these fallacies relate to invalidity, like intra-arguments with structural errors and inconsistencies.

  10. FORMAL FALLACIES

  11. 1) FALLACY OF AFFIRMING THE CONSEQUENT • Itconsists of oneconditionalpremise, a secondpremisethatassertstheconsequent of theconditional, and a conclusionthatassertstheantecedent. • Example: IfNaopeonwaskilled in a planecrash, then he isdead.  premise Napoleonisdead.  premise Therefore, Napoleonwaskilled in a crash. conclusion • Thisfallacy has theform: • If P then Q ( P  Q) • Q , so P

  12. 1) FALLACY OF AFFIRMING THE CONSEQUENT • If A is true, then B is true. • B isstated to be true. • Therefore, A must be true. • Example: • If I am a human, then I am a mammal. • I am a mammal. • Therefore, I am a human.

  13. 1) FALLACY OF AFFIRMING THE CONSEQUENT • Ifmytheoryis true, wewill observe certainresults. premise • We observe theseresults.  Premise • Therefore, mytheoryis true.  Conclusion • Thisisn’tcorrect, unlessthescientistclaimsthatthetruth of theresultslogicallyimplythatthetheoryis true. Instead, he can saythattheresultsconfirmthetheory.

  14. 1) FALLACY OF AFFIRMING THE CONSEQUENT • If you live in Vera, then you live in Spain. • You live in Spain. • So, you live in Vera.

  15. 2) THE FALLACY OF DENYING THE ANTECEDENT • Itconsists in a conditionalpremise, a secondpremisethatdeniestheantecedent of theconditional, and a conclusionthatdeniestheconsequent: • IfNapoleonwaskilled in a planecrash, thenNaopleonisdead.  premise • Naopleonwasnotkilled in a planecrash.  premise • Therefore, Napoleonisnotdead.  conclusion • Thisfallacy has theform: • If P then Q (P  Q) • Not Q, so not P.

  16. 2) THE FALLACY OF DENYING THE ANTECEDENT • If A then B. • Not a. • Therefore, not B. • Example: • If I am in Tokyo, I am in Japan. • I am not in Tokyo. • Therefore, I am not in Japan.

  17. If Luna lives in Vera, thenshelives in Spain.  premise • Luna doesn’tlive in Vera.  premise • Therefore, shedoesn’tlive in Spain. conclusion • Ifyougo to school, youwilllearnsomething.  premise • You do notgo to school.  premise • Youwillnotlearnanything  conclusion • NOTE: Notnecessarily! Onemaylearnout of school!

  18. 2) THE FALLACY OF DENYING THE ANTECEDENT • If A is true, then B is true. • A is NOT true, therefore B is NOT true. • Example: • Ifitis a Yorkie, thenitis a dog. • Itisnot a Yorkie. • Therefore, itisnot a dog.

  19. INFORMAL FALLACIES

  20. 1) Argument against the man (“ad hominem”) • Unfairly attacking a person instead of the issue. • Attacking the character and/or reputation of apposition’s supporters. • The claim that a position is incorrect or an argument invalid because of something not about the position but about the person taking it • Example: “we cannot listen to John’s opinion on global warming because he is a tree hugger”.

  21. Pattern:1. X is a bad person.2. Therefore, X’s argument must be bad.

  22. 1) Argument against the man (“ad hominem”)

  23. 1. A.) Reductio ad Hitlerum(it’s a kind of fallacywhich derives fromtheargumentagainsttheman)

  24. 1) Argument against the man (“ad hominem”)

  25. 2) Tu quoque • Whenanarguerrejectsanotherperson’sargumentorclaimbecausethatpersonis a hypocrite. • Example: - Doctor: Youshould quite smoking. • Patient: Look who’stalking! I willquitwhenyou do. • Pattern: 1. X fails to followhisorherownadvice. 2. Therefore, X‘sclaimorargumentshould be rejected

  26. “Tu quoque” means "you too“. It appeals to hypocrisy, – the argument states that a certain position is false or wrong or should be disregarded because its proponent fails to act consistently in accordance with that position.

  27. 2) TU QUOQUE Example: • Peter: "Basedonthearguments I havepresented, itisevidentthatitismorallywrong to use animalsforfoodorclothing.“ - Bill: "Butyou are wearing a leatherjacket and youhave a roastbeefsandwich in yourhand! How can yousaythatusinganimalsforfood and clothingiswrong!".

  28. 2) Tu quoque

  29. 3) Unquialified Authority or Appeal to authority (“argumentum ad verecundiam”) • When an arguer cites the testimony or belief of an authority who is not necessarily reliable or who is not an expert in the subject at hand. • Example: “He has a PdhD in Physics, that makes him a doctor, so we should ask him if I have Swine Flue.”

  30. 3) Appeal to authority (“argumentum ad verecundiam”) • Appeal to authority is a common type of argument which can be fallacious, such as when an authority is cited on a topic outside their area of expertise or when the authority cited is not a true expert.

  31. 3) Unquialified Authority or Appeal to authority (“argumentum ad verecundiam”)

  32. 4) Appeal to ignorance (“argumentum ad ignorantiam”) • When the premises state that nothing is known with certanity about a certain subject, and the conclsusion states something definite about that subject. • Example: People have been trying for centuries to disprove the claims of astrology. But no one has ever succeeded. So astrology is just nonsense.

  33. 4) Appeal to ignorance(“argumentum ad ignorantiam”)

  34. 4) Appeal to ignorance (“argumentum ad ignorantiam”) •  Assuming that a claim is true because it has not been or cannot be proven false, or vice versa. • It asserts that a proposition is true because it has not yet been proved false (or vice versa). This represents a type of false dichotomy in that it excludes a third option, which is that: there may have been an insufficient investigation, and therefore there is insufficient information to prove the proposition be either true or false.

  35. 5) APPEAL TO PITY (“argumentum ad misericordiam”) • Occurswhenthearguer, instead of providinggenuineevidencefor a conclusion, attempts to getthe conclusión acceptedbyevokingpityfromthelistenerorreader. • Example: our Company isontherocks, financially, ifyousueus, wewillgoout of business, and ourchildrenwillnot be able to gocollege.

  36. 5) APPEAL TO PITY (“argumentum ad misericordiam”) • An argument attempts to induce pity to sway opponents. • It is a fallacy in which someone tries to win support for an argument or idea by exploiting his or her opponent's feelings of pity or guilt. • Appeal to pity is also known as “appeal to emotion”. • "You must have graded my exam incorrectly. I studied very hard for weeks specifically because I knew my career depended on getting a good grade. If you give me a failing grade I'm ruined!" • "Ladies and gentlemen of the jury, look at this miserable man, in a wheelchair, unable to use his legs. Could such a man really be guilty of embezzlement?" • "Lord Byron shouldn't win the poetry competition: he doesn't need the prize money."

  37. 5) Appeal to pity • Whenanarguerattempts to evokefeelings of pityorcompassion, wheresuchfeelings, howeverunderstandable, are notrelevant to thetruth of thearguer’s conclusión. • Example: Student to Lecturer: I know I missedhalfyour clases and failedallmyquizzes. Firstmycatdied. Thenmygirlfriendtold me she has foundsomeoneelse. Withall I wentthroughthissemester, I don’tthink I reallydeservean F in mymarks. Any chance mightcut me someslack and changemy grade to a C or a D? • Pattern: 1. P ispresented, withtheintent to createpity. 2. Thereforeclaim C is true.

  38. 6) False cause (“Post Hoc”) • Citing a false orremote cause to explain a situation. • “Afterthis, thereforebecause of this” • Assumingthatbecausetwothingshappened, thefirstonecausedthesecondone. • Example: “Every time mybrothe Bill uses hairspray, itisanextremelyhotday”. “Therefore, theincreasing global warming in thepastdecadeisbecause more teenagers are usinghairspray”

  39. 6) False cause (“Post Hoc”)

  40. 6) False cause (“Post Hoc”) • It is a faulty assumption that correlation between two variables implies that one causes the other. • "Since event Y followed event X, event Y must have been caused by event X."

  41. 6) False cause (“Post Hoc”)

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