LoveisaFallacy谬论.ppt

LoveisaFallacy,Whatisafallacy?,Afallacyistheuseofpoor,orinvalidreasoningfortheconstructionofanargument.Itisalsousedtorefertoanargumentwhichappearstobecorrectbutisnot.,Anargumentinlogicpresentsevidenceinsupportofsomethesisorconclusion.Anargumenthastwocomponents:aconclusionandcertainpremises.Theconclusionissaidtobedrawnorinferredfromthepremises.Anargumentisdeductivelyvalidwhenitspremisesprovideevidencefortheconclusion.Anargumentthatfailstobeconclusivelydeducedisinvalid,itissaidtobefallacious.,Argument,LogicFallacies,1.DictoSimpliciter（绝对判断）2.HastyGeneralization（轻率归纳）3.PostHoc（错误因果）4.ContradictoryPremises（矛盾前提）,1.DictoSimpliciter,Polly,Isaidgently,theargumentisafallacy.Exerciseisgoodisanunqualifiedgeneralization.Forinstance,ifyouhaveheartdisease,exerciseisbad,notgood.Manypeopleareorderedbytheirdoctorsnottoexercise.Youmustqualifythegeneralization.Youmustsayexerciseisusuallygood,orexerciseisgoodformostpeople.OtherwiseyouhavecommittedaDictoSimpliciter.Doyousee?,1.DictoSimpliciter（绝对判断）DictoSimpliciterisanargumentbasedonanunqualifiedgeneralization.Theargumentappliesageneralruletoaparticularcaseinwhichsomespecialcircumstancesmaketheruleinapplicable.,Examples,Womenareonaveragenotasstrongasmenandlessabletoperformwellpolitically.Therefore,womencantpulltheirweightingovernmentwork.虽然女性确实在政界担任较少工作，但这不意味着女性群体中所有的人都是这样。JapanesewagedawartoChinese,whichhadnothingtodowithhumanitybuteverythingtodowithaggression.ThereforeeveryJapaneseisguiltyandshouldbecondemned.虽然日本侵华的邪恶战争任历历在目，但并不是所有的日本人都有罪，都应该受到谴责。,2.HastyGeneralization,NextwetakeupafallacycalledHastyGeneralization.Listencarefully:YoucantspeakFrench.PeteyBurchcantspeakFrench.ImustthereforeconcludethatnobodyattheUniversityofMinnesotacanspeakFrench.Really?saidPolly,amazed.Nobody?Ihidmyexasperation.Polly,itsafallacy.Thegeneralizationisreachedtoohastily.Therearetoofewinstancetosupportsuchaconclusion.,2.HastyGeneralization（轻率归纳）Hastygeneralizationisafallacyinwhichaconclusionisnotlogicallyjustifiedbysufficientorunbiasedevidence.Ahastygeneralizationalwaysproceedsfromtheparticulartothegeneral.,HastyGeneralization,Itspattern:XistrueforA.XistrueforB.XistrueforC.XistrueforD.Therefore,XistrueforE,F,G,etc.,Example,Mikefailedbiologyexam.Janefailedbiologyexam.Mariafailedbiologyexam.Therefore,Iconcludethatmoststudentswhotakebiologyexamwillfailit.,Analysis,Inunderstandingandcharacterizinggeneralsituations,alogiciancannotnormallyexamineeverysingleexample.However,theexamplesusedininductivereasoningshouldbetypicaloftheproblemorsituationathand.MaybeMike,Jane,andMariaareexceptionallypoorstudents.Maybetheyweresickandmissedtoomanylectures.Ifalogicianwantstomakethecasethatmoststudentswillfailbiologyexam,sheshould(a)getaverylargesample-atleastonelargerthanthreeor(b)ifthatisntpossible,shewillneedtogooutofhiswaytoprovetothereaderthatherthreesamplesaresomehowrepresentativeofthenorm.,3.PostHoc,Listentothis:LetsnottakeBillonourpicnic.Everytimewetakeitoutwithus,itrains.Iknowsomebodyjustlikethat,sheexclaimed.Agirlbackhome-EulaBecker,hernameis.Itneverfails.Everysingletimewetakeheronapicnic.Polly,Isaidsharply,itsafallacy.EulaBeckerdoesntcausetherain.Shehasnoconnectionwiththerain.YouareguiltyofPostHocifyoublameEulaBecker.,3.PostHoc（错误因果）PostHocisafallacyinwhichoneeventissaidtobethecauseofalatereventsimplybecauseitoccurredearlier.PostHocisafallacywiththefollowingform:1.AoccursbeforeB.2.ThereforeAisthecauseofB.,Examples,Joanisscratchedbyacatwhilevisitingherfriend.Twodayslatershecomesdownwithafever.Joanconcludesthatthecatsscratchmustbethecauseofherillness.Mostyoungcriminalswatchviolentmoviesbeforetheycommittheircrimes;obviously,violentmoviesleadtojuveniledelinquency.甲事情发生在乙事情之前，这并不代表着先发生的甲事情就是后发生的乙事情的原因。,4.ContradictoryPremises,IfGodcandoanything,canHemakeastonesoheavythatHewontbeabletoliftit?Ofcourse,sherepliedpromptly.ButifHecandoanything,Hecanliftthestone,Ipointedout.Yeah,shesaidthoughtfully.Well,thenIguessHecantmakethestone.ButHecandoanything,Iremindedher.Shescratchedherpretty,emptyhead.Imallconfused,sheadmitted.Ofcourseyouare.Becausewhenthepremisesofanargumentcontradicteachother,therecanbenoargument.Ifthereisanirresistibleforce,therecanbenoimmovableobject.Ifthereisanimmovableobject,therecanbenoirresistibleforce.Getit?,4.ContradictoryPremises（矛盾前提）ContradictoryPremisesisanargumentthatdrawsaconclusionfrominconsistentorincompatiblepremises.Essentially,apropositioniscontradictorywhenitassertsanddeniesthesamething.,Sometimesitisdifficulttodistinguishbetweenrealandapparentincompatiblepremises.Letslookattheexamplebelow.Afathersaidtohisson:youcantrustnoone.,Analysis,Thefatherwhoistryingtoconvincehischildthatnooneshouldbetrustedisobviouslymakinganexceptionofhimself.Ifhereallyweremakingincompatibleclaims(sinceyoushouldtrustnoone,andyoushouldtrustme),norationalconclusioncouldorsho