a concise introduction to logic - hurley 7th ed

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1、1BasicConcepts1.1Arguments,Premises,andConclusionsLogicmaybedefinedasthesciencethatevaluatesarguments.Allofusencounterargumentsinourday-to-dayexperience.Wereadtheminbooksandnewspapers,hearthemontelevision,andformulatethemwhencommunicatingwithfriendsandassociates.Theaimoflogicistodevelopasy

2、stemofmethodsandprinciplesthatwemayuseascriteriaforevaluatingtheargumentsofothersandasguidesinconstructingargumentsofourown.Amongthebenefitstobeexpectedfromthestudyoflogicisanincreaseinconfidencethatwearemakingsensewhenwecriticizetheargumentsofothersandwhenweadvanceargumentsofourown.Anargum

3、ent,asitoccursinlogic,isagroupofstatements,oneormoreofwhich(thepremises)areclaimedtoprovidesupportfor,orreasonstobelieve,oneoftheothers(theconclusion).Allargumentsmaybeplacedinoneoftwobasicgroups:thoseinwhichthepremisesreallydosupporttheconclusionandthoseinwhichtheydonot,eventhoughtheyare

4、claimedto.Theformeraresaidtobegoodarguments(atleasttothatextent),thelatterbadarguments.Thepurposeoflogic,asthesciencethatevaluatesarguments,isthustodevelopmethodsandtechniquesthatallowustodistinguishgoodargumentsfrombad.Asisapparentfromtheabovedefinition,theterm‘‘argument’’hasaveryspecificm

5、eaninginlogic.Itdoesnotmean,forexample,amereverbalfight,asonemighthavewithone’sparent,spouse,orfriend.Letusexaminethefeaturesofthisdefinitioningreaterdetail.Firstofall,anargumentisagroupofstatements.Astatementisasentencethatiseithertrueorfalse—inotherwords,typicallyadeclarativesentenceorase

6、ntencecomponentthatcouldstandasadeclarativesentence.Thefollowingsentencesarestatements:Aluminumisattackedbyhydrochloricacid.BroccoliisagoodsourceofvitaminA.ArgentinaislocatedinNorthAmerica.NapoleonprevailedatWaterloo.SRembrandtwasapainterandShelleywasapoet.NLThefirsttwostatementsaretrue,th

7、esecondtwofalse.Thelastoneexpressestwostatements,bothofwhicharetrue.Truthandfalsityarecalledthetwopossibletruthvaluesofastatement.Thus,thetruthvalueofthefirsttwostatementsistrue,thetruthvalueofthesecondtwoisfalse,andthetruthvalueofthelaststatement,aswellasthatofitsco