Chapter10:ReasoningaboutCauses
InThisSlideshow
A. CausalityB. Mill'sMethodsC. Limita:onsofMill'sMethodsD. Theore:calandExperimentalScienceE. InferencetotheBestExplana:onF. HypothesisTes:ng,Experiments,and
Predic:onsG. ScienceandSupers::on
Causality
• Cause-effectrela:onshipsinvolvemanyfactors:Therockbrokethewindow.
Weight?Velocity?Angle?Density?Strength?
• Causalnetwork:Asetofcondi:onsthatbringaboutaneffect.Somewaysofdescribingcondi:ons:– Normalstate:Thehistoricalinforma:onregardinganobject.– Abnormalstate:Adras:cchangeinthenormalstateregardinganobject.– Precipita>ngcause:Theobjectoreventdirectlyinvolvedinbringingaboutaneffect.– Remotecause:Somethingthatisconnectedtotheprecipita:ngcausebyachainofevents.
Mill'sMethodsJohnStuartMill(1806–73)presentedfivemethodsformakingcausalinduc:veargumentsinhisSystemofLogic:
1. Methodofagreement2. Methodofdifference3. Jointmethodofagreementand
difference4. Methodofresidues5. Methodofconcomitantvaria:ons
MethodofAgreement• Themethodthatlooksattwoormoreinstancesofan
eventtoseewhattheyhaveincommon.Threepeoplegetfoodpoisoninginarestaurant:
• Cri>cism:Thismethodmayhelpsnarrowthesearchbutitdoesnotprovideconclusiveproofthatwehavefoundthecause.Itoffersonlypar:al,tenta:veinduc:veevidence.
MethodofDifference• Themethodthatlooksforwhatalltheinstancesofan
eventdonothaveincommon.Whodidnotgetfoodpoisoning?(theeffect)
• Cri>cism:Thismethodiden:fiesasufficientcondi7onastheprobablecause,oraprobablecausalfactor,buts:lldoesnotprovideconclusiveproof.
JointMethodofAgreementandDifference• Iftwoormoreinstancesofaneventhaveonlyonefactorincommon,
whiletheinstancesinwhichitdoesnotoccurallsharetheabsenceofthatfactor,thenthefactorisalikelycause.
• Assessment:Theconclusionallowsustoassertthatthecausewas
probablybothasufficientandnecessarycondi7onfortheeffect.
HaveeffectoroutcomeincommonDoesnothaveeffectoroutcomeincommon
MethodofResidues
• Themethodthatsubtractsfromacomplexsetofeventsthosepartsthatalreadyhaveknowncauses.– Subtractwhatisknownfrompastexperience:
– Whateverremainsisthemostlikelycauseoftheremainderoftheeffect.
MethodofConcomitantVaria:ons• Themethodthatlooksfortwofactorsthatvarytogether.– Correla>on:Acorrespondencebetweentwosetsofobjects,events,orsetsofdata.
Isolateonevariable(speed),keepothersconstant:Result:speedandMPGvarytogether(arecorrelated)
• Cri>cism:Everycause-effectrela7onshipisacaseofcorrela7on,butnoteverycorrela7onisacause-effectrela7onship.
CheckYourUnderstanding(a)
• ExampleBreathingelevatedozonelevelscausesvulnerablepopula7ons—suchastheelderlyandpersonswithdiabetesorheartdisease—tobeatheightenedriskofheartaLack,stroke,andsuddendeathfromarrhythmias.
• AnswerAsufficientcondi7on
Limita:onsofMill'sMethods
• FalsecausefallaciescanoccurifMill’smethodsareappliedsimplis:cally(seeChapter3).
• Mill'smethodshelprevealanecessaryingredientincausa:on(acorrela7on),butdonotprovidesufficientevidenceofcausa:on.
• Understandingthehowandwhyofcausalfunc:onsgoesbeyondiden:fyingcause-effectrela:onshipstothedevelopmentoftheoriesandhypotheses—thebasisofscien:ficreasoning.
Theore:calandExperimentalScience• Interplayofscienceandtechnologyfollowsarepea:ngpadern:
• Twoaspectsofscienceareinvolvedinthedevelopmentofnewinven:onsandtechnologies:– Theore>calscience:Proposesexplana:onsfornaturalphenomena.Mendel’sTheoryofInheritance
– Experimentalscience:Teststheexplana:onsproposedbytheore:calscience.Experimentsingene:cs
InferencetotheBestExplana:on
• Abduc>on:Theprocessthatoccurswhenweinferexplana:onsforcertainfacts.
• Inferencetothebestexplana>on:Reasoningfromthepremisethatahypothesiswouldexplaincertainfactstotheconclusionthatthehypothesisisthebestexplana:onforthosefacts.– Thebesthypothesisshouldprovideacausalexplana:onbasedon:• Historicaldata• Contemporaryknowledge• Strongprobability
HypothesisTes:ng,Experiments,andPredic:ons
• Scien:fictheoriesmust:– Standuptosevereandrepeatedtes7ngofhypotheses
– Providecoherentandeffec:veexplana7ons– Providecorrectpredic7ons– Helptodiscovernewfactsabouttheworld
ControlledExperiments
Oneinwhichmul:pleexperimentalsetupsdifferbyonlyonevariable,therebyhelpingtouncovercausalrela:onships.– Experimentalgroup:Thegroupthatgetsthevariablebeingtested.
– Controlgroup:Thegroupinwhichthevariablebeingtestediswithheld.
DeterminingCausality
Noneofthesefivecriteriaaloneissufficienttoestablishacause-effectrela:onship;answerstoallfivetogetherestablishgroundsforacause-effectrela:onship.
DeterminingCausality
Detailsaboutthefivecriteria:1. Acorrela7onisrequired,butcannotinitselfestablisha
causalrela:onship.2. (and3.)The7melag/spa7aldistancebetweencauseand
effectmustbeconsidered(thelongerthe:melag/greaterthespa:aldistance,themorethesitua:oncanbeinterruptedbyothervariables).
4. Requiresthat“XcausedY”bebackedby:(1)XwassufficienttobringaboutY;and(2)XwasnecessaryforY(withoutX,Ywouldnothaveoccurred).
5. Rulingoutplausiblealterna:veexplana:onsmeansthattheevidencebothrefutesrivalclaimsandconfirmsthehypothesis.
TheNeedforaFairTest
• Agoodtestofahypothesisinvolvesmakingapredic7on.• Thetruthorfalsityofthepredic:onprovidesevidence
torefute(disconfirmorfalsify)orsupport(confirmorcorroborate)thehypothesis.
• Agoodpredic:onhelpsjudgethestrengthofacausalargument.Afailedpredic7onmeansthehypothesismustberejectedorrevised.
VerifiablePredic:ons
Verifiablepredic>on:Onewherethepredic:on,ifitistrue,mustincludeanobservableevent.
Everyoneinthehousegotsickfornoapparentreason.Hypothesis1:Ahighdegreeofradioac:vityinthehouseiscausingtheillness.
Predic:on:UseaGeigercountertofindhighreadingsofradioac:vity.
Hypothesis2:Adisease-causingghostishaun:ngthishouse.
Predic:on:Isthereamethodtoobtainobservableevidence?
NontrivialPredic:onsNontrivialpredic>on:Requiresreferencetobackgroundknowledge(everythingweknowtobetrue).
Halley’shypothesis:Cometsreappearinregularcycles.Backgroundknowledge:NewtonianTheoryPredic:on:Acometwillreappearin1758inapreciseloca:on.
Thepredic7onisspecificandunlikelytobetruewithoutthishypothesis.
Connec:ngtheHypothesisandPredic:on
Theremustbeadirectconnec:onbetweenthehypothesisandthepredic:oninordertotransferthetruthvaluefromthepredic:onbacktothehypothesis.– Halleyno:cedapadern:acometappearedinaspecificplaceintheskyin1682,1606,and1530.
– Halleyconjecturedthattheywereinstancesofthesamecomet(hishypothesis).
– Fromthisdataandbackgroundknowledge(NewtonianTheory),Halleycalculatedthenextreturnofthecomet,leadingtoaspecificpredic:on.
ScienceandSupers::on• Applyingthecriteriafortes:nghypothesescanhelpexposefalsebeliefs.– Evolu:onarytheory:
• Highlytestable• Repeatedlytested• Successfulandfruioulinexplainingalargepartoftheworld
– Crea:onismor“intelligentdesign”:• Doesnotgeneratetestablehypotheses• Isnotfruioulinexplaininganythingnewaboutthephysicalworld
• Doesnotmeetthebasiccriteriaforascien:fictheory
TheAllureofSupers::on
• Supers::ousbeliefsclaimcausalrela:onshipsbetweeneventswherenoneexist.– Predic:onscannottransfertruthvaluebacktoahypothesisiftheyarenottheproductofarepeatableexperiment.
• Thescien:ficprocessispar7alandtenta7ve,withevidenceaccumula:ngoveralong:me;mistakesarerevealedbytheresultsofrepeatedexperiments.
CheckYourUnderstanding(b)(ForDiscussion)Analyzeandevaluatethefollowingcase.Whatisthehypothesis/predic:on/experiment?
Thefollowingcasehasbeencitedinsupportofthehypothesisthatpyramidshavespecialpowers.Ayoungwomanwhowashavingdifficultywithhercomplexionwastoldtokeepapitcherofwaterunderapyramidandthenwashherfaceinthatwater,withonlythemildestsoap,onceinthemorningandonceintheevening.Shewasalsotoldtoputnothingelseonherface,nocreamsormedica7onsofanykindandnomakeup.Althoughshehasbeeninthehabitofusingmakeup,sheagreedtotheexperiment.Withintwoweekstherewasaclearlyno7ceableimprovementinhercomplexion.—Understanding Scientific Reasoning,ed.R.Giereetal.,2006
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