▁precisely ▁that ▁price ▁which , ▁according ▁to ▁Marx , ▁is ▁const rained ▁by ▁the ▁law ▁of ▁value , ▁i . e . ▁by ▁the ▁proportional ities ▁of ▁human ▁labour - time ▁reflected ▁in ▁the ▁cost ▁structure ▁of ▁products . ▁ ▁Law ▁of ▁value ▁in ▁capital ism ▁Marx ▁arg ues ▁that , ▁as ▁economic ▁exchange ▁develop s ▁and ▁mark ets ▁expand ▁while ▁traditional ▁methods ▁of ▁production ▁are ▁destroyed ▁and ▁replaced ▁by ▁commercial ▁practices , ▁the ▁law ▁of ▁value ▁is ▁modified ▁in ▁its ▁operation . ▁ ▁Production ▁prices ▁ ▁Thus , ▁the ▁capital ist ▁mode ▁of ▁production ▁is ▁a ▁type ▁of ▁economy , ▁in ▁which ▁both ▁inputs ▁and ▁outputs ▁of ▁production ▁have ▁become ▁market ed ▁goods ▁and ▁services ▁( or ▁comm od ities ) ▁which ▁are ▁bought ▁and ▁sold ▁freely . ▁Here , ▁capital ists ▁do ▁not ▁make ▁money ▁simply ▁from ▁trad ing ▁or ▁rent ing , ▁but ▁from ▁the ▁capital ization ▁of ▁production ▁itself . ▁Product s ▁and ▁labour ▁are ▁purchased ▁to ▁manufact ure ▁new ▁products ▁which ▁have ▁a ▁higher ▁value ▁in ▁the ▁market ▁than ▁their ▁cost ▁price , ▁resulting ▁in ▁a ▁profit ▁from ▁the ▁added ▁value . ▁In ▁such ▁an ▁economy , ▁Marx ▁arg ues , ▁what ▁directly ▁regul ates ▁the ▁economic ▁exchange ▁of ▁new ▁labour - products ▁is ▁not ▁the ▁law ▁of ▁value , ▁but ▁their ▁prices ▁of ▁production . ▁The ▁theoretical ▁problem ▁which ▁Marx ▁then ▁tries ▁to ▁tack le ▁is ▁how ▁the ▁movements ▁of ▁production ▁prices ▁across ▁time ▁are ▁never theless ▁reg ulated ▁by ▁the ▁law ▁of ▁value . ▁That ▁was