Sound and Cogent Arguments - FutureLearn

Another Cogent Argument Example. I had coffee this morning. Therefore, it's quite likely that I drank something this morning. This is a strong argument with ... Skipmainnavigation Allnews FutureLearnLocal Press Insights HowTo WhatIs Home/Business&Management/BusinessStrategy/LogicalandCriticalThinking/SoundandCogentArguments Learnmoreaboutthiscourse. SoundandCogentArguments Validityandstrengthofargumentsdonotontheirowntelluswhetherargumentsaregoodorbad.We’veactuallyseenrubbishargumentsthatwerevalid.That’swhyweneedtointroducetwofurtherconceptsforarguments:beingsoundandbeingcogent. ©PatrickGirard,UniversityofAuckland Sofarwehavetalkedaboutthekindofsupportthatcanbegivenforconclusions:deductiveandnon-deductive. Wedefinedanargumentasbeingvalidifit’sadeductiveargumentforwhichthepremisessucceedinprovidingconclusivesupportfortheconclusion. Andwedefinedanargumentasbeingstrongifit’sanon-deductiveargumentinwhichthepremisessucceedinprovidingstrongsupportfortheconclusion. Bythat,wemeanthat,ifthepremisesaretrue,thentheconclusionwouldbegiventheappropriatesupportforalsobeingtrue. Butwehaven’tsaidanythingyetaboutwhetherthepremisesaretrueornot.Thisiswhatwedowhenweevaluatewhetherargumentsaresoundorcogent. SoundandCogentArguments Wanttokeeplearning? ThiscontentistakenfromTheUniversityofAucklandonlinecourse, LogicalandCriticalThinking ViewCourse Validityandstrengthofargumentsdonotontheirowntelluswhetherargumentsaregoodorbad.We’veactuallyseenrubbishargumentsthatwerevalid.That’swhyweneedtointroducetwofurtherconceptsforarguments:beingsoundandbeingcogent. SoundArguments Definition:Asoundargumentisavalidargumentthathastruepremises. Firstly,asoundargumentisadeductiveargument.It’stryingtoestablishconclusivesupportforitsconclusion.Secondly,theargumentisvalid:thepremises,iftrue,wouldguaranteethattheconclusionisalsotrue.Andontopofallthat,thepremisesareactuallytrue.Therefore,asoundargumentguaranteesthatitsconclusionistrue. Wesaythatasoundargumentisagoodargument.Itisagoodargumentbecauseitguaranteesthattheconclusionistrue.Itwouldbeirrationalforyounottobelievetheconclusionofasoundargument. Ofcourse,soundargumentsareveryrare,becausethey’reveryhardtoestablish.But,someargumentsaresound. SoundArgumentExample TheprovinceofQuébecispartofCanada.PatrickwasborninQuébec.Therefore,PatrickwasborninCanada. Thisisavalidargument.Canyouseewhy? Furthermore,thepremisesaretrue:QuébecisindeedpartofCanada,andPatrickwasindeedborninQuébec.Hence,youcanbeabsolutelycertainthatPatrickwasborninCanada,andyououghttobelievethatPatrickwasborninCanada.There’snowayaroundit. FurtherSoundArgumentExamples Idrankcoffeethismorning;therefore,Idranksomethingthismorning. PatrickgotmarriedonJanuary4,2014.PatrickhasnotbeendivorcedandPatrickisnotawidower.Therefore,Patrickisnotabachelor. ItistruethatPatrickgotmarriedonJanuary4,2014,thathehasnotdivorcedandthatheisnotawidower.SoPatrickisnotabachelorbecauseabachelorisanunmarriedmale,bydefinition. CogentArguments Now,whataboutnon-deductivearguments?Fornon-deductivearguments,weintroducethenotionofacogentargument. Definition:Acogentargumentisastrongnon-deductiveargumentthathastruepremises. Andagain,wesaythatcogentargumentsaregood.Acogentargumentisbydefinitionnon-deductive,whichmeansthatthepremisesareintendedtoestablishprobable(butnotconclusive)supportfortheconclusion. Furthermore,acogentargumentisstrong,sothepremises,iftheyweretrue,wouldsucceedinprovidingprobablesupportfortheconclusion.Andfinally,thepremisesareactuallytrue.Sotheconclusionindeedreceivesprobablesupport. CogentArgumentExample PatrickwasborninNorthAmericaandPatrickwasn’tborninMexico.It’sthusquiteprobablethatPatrickwasbornintheUSA. Thatisacogentargument.IfallyouknowaboutPatrickiswhat’scontainedinthepremises,andthosepremisesaretrue(theyare!),thenthat’safairlystrongargument,becausethepopulationoftheUSAisover300000000,whereasthatofCanadaisunder40000000.ThismeansthattheoddsthatPatrickwasbornintheUSAareroughly88%,whichmakesthesupportfortheconclusionquitestrong.Furthermore,thepremisesaretrue.Therefore,theargumentiscogent,andsoitisagoodargument. Thismeansthatwecanhavegoodargumentsthathavefalseconclusions! AnotherCogentArgumentExample Ihadcoffeethismorning.Therefore,it’squitelikelythatIdranksomethingthismorning. Thisisastrongargumentwithtruepremises,soitiscogentandtherefore,good.Buttheconclusionisnotguaranteed.ItmaybethatIhadcoffeethismorningbyeatingit,orbysomeothermeans.Butofcourse,thisisveryunlikely,sotheargumentisstrong,thoughit’sstillpossiblethattheconclusionisfalse.Still,thisiscogentandtherefore,agoodargument. ©PatrickGirard,UniversityofAuckland Wanttokeeplearning? 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