Ontheotherhand，nochangeinthisproductivenessaffectsthelabourrepresentedbyvalue。Sinceproductivepowerisanattributeoftheconcreteusefulformsoflabour，ofcourseitcannolongerhaveanybearingonthatlabour，sosoonaswemakeabstractionfromthoseconcreteusefulforms。Howeverthenproductivepowermayvary，thesamelabour，exercisedduringequalperiodsoftime，alwaysyieldsequalamountsofvalue。Butitwillyield，duringequalperiodsoftime，differentquantitiesofvaluesinuse;more，iftheproductivepowerrise，fewer，ifitfall。Thesamechangeinproductivepower，whichincreasesthefruitfulnessoflabour，and，inconsequence，thequantityofuse—valuesproducedbythatlabour，willdiminishthetotalvalueofthisincreasedquantityofuse—values，providedsuchchangeshortenthetotallabour—timenecessaryfortheirproduction;andviceversâ。
Ontheonehandalllabouris，speakingphysiologically，anexpenditureofhumanlabour—power，andinitscharacterofidenticalabstracthumanlabour，itcreatesandformsthevalueofcommodities。Ontheotherhand，alllabouristheexpenditureofhumanlabour—powerinaspecialformandwithadefiniteaim，andinthis，itscharacterofconcreteusefullabour，itproducesuse—values。[16]
SECTION3THEFORMOFVALUEOREXCHANGE—VALUE
Commoditiescomeintotheworldintheshapeofuse—values，articles，orgoods，suchasiron，linen，corn，&c。Thisistheirplain，homely，bodilyform。Theyare，however，commodities，onlybecausetheyaresomethingtwo—fold，bothobjectsofutility，and，atthesametime，depositoriesofvalue。Theymanifestthemselvesthereforeascommodities，orhavetheformofcommodities，onlyinsofarastheyhavetwoforms，aphysicalornaturalform，andavalue—form。
TherealityofthevalueofcommoditiesdiffersinthisrespectfromDameQuickly，thatwedon’tknow\"wheretohaveit。\"Thevalueofcommoditiesistheveryoppositeofthecoarsematerialityoftheirsubstance，notanatomofmatterentersintoitscomposition。Turnandexamineasinglecommodity，byitself，aswewill，yetinsofarasitremainsanobjectofvalue，itseemsimpossibletograspit。If，howeverwebearinmindthatthevalueofcommoditieshasapurelysocialreality，andthattheyacquirethisrealityonlyinsofarastheyareexpressionsorembodimentsofoneidenticalsocialsubstance，viz。，humanlabour，itfollowsasamatterofcourse，thatvaluecanonlymanifestitselfinthesocialrelationofcommoditytocommodity。Infactwestartedfromexchange—value，ortheexchangerelationofcommodities，inordertogetatthevaluethatlieshiddenbehindit。Wemustnowreturntothisformunderwhichvaluefirstappearedtous。