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