Logical-Fallacies逻辑谬误

Logic(partfour)FallaciesArguments,likemen,areoftenpretenders.—PlatoWhatarefallacies?Fallaciesaredefectsthatweakenarguments.Bylearningtolookfortheminyourownandothers'writing,youcanstrengthenyourabilitytoevaluatetheargumentsyoumake,read,andhear.twospecialnotesaboutfallaciesFallaciousargumentsarevery,verycommonandcanbequitepersuasive,atleasttothecasualreaderorlistener.Youcanfinddozensofexamplesoffallaciousreasoninginnewspapers,advertisements,andothersources.Therearemanydifferentkindsoffallacieswithdifferentnames.ArgumentfromIgnoranceDefinitionArgumentfromIgnoranceassertsthatapropositionistruebecauseithasnotbeenprovedfalse,orthatitisfalsebecauseithasnotbeenprovedtrue.Inscienceandlogic,wemustverifythetruthorfalsehoodofpropositions;beforethat,nothingcanbeasserted.Injurisprudence,however,thereisanexception:apersonisalwaysregardedasinnocentbeforehe/sheisprovedguilty.ExamplesYoucan’tprovethatGodexists.Thereforehedoesn’texist.Youcan’tprovethatGoddoesn’texist.Thereforeheexists.thestoryofGalileoHastyGeneralizationDefinitionmakingassumptionsaboutawholegrouporrangeofcasesbasedonasamplethatisinadequate(usuallybecauseitisatypicalorjusttoosmall).Stereotypesaboutpeople(“pilotstudentsarehandsome,gradstudentsarenerdy,etc.)arecommonexamplesofhastygeneralization.ExampleMyroommatesaidherphilosophyclasswashard,andtheoneI'minishard,too.Allphilosophyclassesmustbehard!Twopersons’experiencesare,inthiscase,notenoughonwhichtobaseaconclusion.Smokingcausescancerbecausemyfatherwasasmokerandhediedoflungcancer.TipAskyourselfwhatkindofsampleyou'reusing:Areyourelyingontheopinionsorexperiencesofjustafewpeople,oryourownexperienceinjustafewsituations?Ifso,considerwhetheryouneedmoreevidence,orperhapsalesssweepingconclusion.Noticethatinthepreviousexample,themoremodestconclusionSomephilosophyclassesarehardforsomestudentswouldnotbeahastygeneralization.AccidentdefinitionWhenweapplyageneralizationtoindividualcasesthatitdoesnotproperlygovern,wecommitthefallacyofaccident.Almosteverygoodrulehasappropriateexceptions;wearguefallaciouslywhenwereasononthesuppositionthatsomerulesapplywithuniversalforce.Accidentistheoppositeoffalsegeneralization.ExampleIamsuretheirambassadorwillbereasonableaboutthematter.Afterall,manisarationalanimal.Manisarationalanimal.That’strue,becausewehavereason.Butthatdoesnotmeanallmenbehaverationallyunderallcircumstances.“Allgeneralizationsarefalse,includingthisone.”—MarkTwainFalsecause/Posthoc(假性因果)DefinitionassumingthatbecauseBcomesafterA,AcausedBOfcourse,sometimesoneeventreallydoescauseanotheronethatcomeslater.forexample,ifIregisterforaclass,andmynamelaterappearsontheroll,it'struethatthefirsteventcausedtheonethatcamelater.Butsometimestwoeventsthatseemrelatedintimearen'treallyrelatedascauseandeffect.Thatis,correlationisn'tthesamethingascausation.ExamplesPresidentJonesraisedtaxes,andthentherateofviolentcrimewentup.Jonesisresponsiblefortheriseincrime.Theincreaseintaxesmightormightnotbeonefactorintherisingcrimerates,buttheargumenthasn'tshownusthatonecausedtheother.Afloodhappenedafterthecometappeared;therefore,thecometcausedtheflood.misunderstandingofthelunareclipseTipsToavoidtheposthocfallacy,thearguerwouldneedtogiveussomeexplanationoftheprocessbywhichthetaxincreaseissupposedtohaveproducedhighercrimerates.That'swhatyoushoulddotoavoidcommittingthisfallacy:IfyousaythatAcausesB,youshouldhavesomethingmoretosayabouthowAcausedBthanjustthatAcomesfirstandBcomeslater!Weak/FalseAnalogy(错误类比)DefinitionManyargumentsrelyonananalogybetweentwoormoreobjects,ideas,orsituations.Ifthethingsthatarebeingcomparedaren'treallyalikeintherelevantrespects,theanalogyisaweakone,andtheargumentthatreliesonitcommitsthefallacyofweakanalogy.ExampleGunsarelikehammers—they'rebothtoolswithmetalpartsthatcouldbeusedtokillsomeone.Andyetitwouldberidiculoustorestrictthepurchaseofhammers—sorestrictionsonpurchasinggunsareequallyridiculous.Whilegunsandhammersdosharecertainfeatures,thesefeatures(havingmetalparts,beingtools,andbeingpotentiallyusefulforviolence)arenottheonesatstakeindecidingwhethertorestrictguns.Rather,werestrictgunsbecausetheycaneasilybeusedtokilllargenumbersofpeopleatadistance.Thisisafeaturehammersdonotshare—it'dbehardtokillacrowdwithahammer.Thus,theanalogyisweak,andsoistheargumentbasedonit.ExamplesMindandrivers,canbebothbroad.Itisaknownfactthatthebroadertheriver,theshalloweritis.Thereforeitmustbetrue,thatthebroaderthemindis,theshalloweritis.Employeesandnailsarethesame.Asitisnecessarytohitnailsontheheadinordertomakethemwork,thesamemustbedonewithemployees.TipIdentifywhatproperties/attributesareimportanttotheclaimyou'remaking,andseewhetherthetwothingsyou'recomparingbothsharethoseproperties.Thisshowstheimportanceofrelevance.Appealtoinappropriateauthority(诉诸不当权威)DefinitionOftenweaddstrengthtoourargumentsbyrefer-ringtorespectedsourcesorauthoritiesandexplainingtheirpositionsontheissueswe'rediscussing.Thisisquiteproperandevenencouragedinacademicresearch.If,however,wetrytogetreaderstoagreewithussimplybyimpressingthemwithafa