▁ ▁Capital ist ▁economic ▁exchange , ▁Marx ▁arg ues ▁( contr ary ▁to ▁David ▁Ric ardo ' s ▁theory ), ▁is ▁not ▁a ▁simple ▁exchange ▁of ▁equivalent ▁values . ▁ ▁It ▁a ims ▁not ▁to ▁trade ▁goods ▁and ▁services ▁of ▁equivalent ▁value , ▁but ▁instead ▁to ▁make ▁money ▁from ▁the ▁trade ▁( this ▁is ▁called ▁capital ▁accum ulation ). ▁The ▁aim ▁is ▁to ▁buy ▁as ▁cheap ly ▁as ▁possible , ▁and ▁sell ▁as ▁dear ▁as ▁possible , ▁under ▁the ▁compet itive ▁constraint ▁that ▁everybody ▁has ▁the ▁same ▁objective . ▁The ▁effect ▁is ▁that ▁the ▁whole ▁cost - structure ▁of ▁production ▁perman ently ▁includes ▁profit ▁as ▁an ▁additional ▁imp ost . ▁ ▁In ▁an ▁overall ▁sense , ▁Marx ▁arg ues ▁the ▁subst ance ▁of ▁this ▁imp ost ▁is ▁the ▁un pa id ▁sur plus ▁labour ▁performed ▁by ▁the ▁working ▁class ; ▁part ▁of ▁society ▁can ▁live ▁off ▁the ▁labour ▁of ▁others ▁due ▁to ▁their ▁ownership ▁of ▁property . ▁ ▁In ▁this ▁situation , ▁output ▁values ▁produced ▁by ▁enter pr ises ▁will ▁typically ▁devi ate ▁from ▁output ▁prices ▁real ised . ▁Market ▁competition ▁for ▁a ▁given ▁demand ▁will ▁imp ose ▁a ▁r uling ▁price - level ▁for ▁a ▁type ▁of ▁output , ▁but ▁the ▁different ▁compet ing ▁enter pr ises ▁producing ▁it ▁will ▁take ▁more ▁or ▁less ▁labour ▁to ▁produce ▁it , ▁depending ▁on ▁product ivity ▁levels ▁and ▁techn ologies ▁they ▁use . ▁Con sequently , ▁output ▁values ▁produced ▁by ▁different ▁enter pr ises ▁( in ▁terms ▁of ▁labour - time ) ▁and ▁output ▁prices