▁they ▁did ▁not ▁explain ▁it ▁consist ently ▁( see ▁below ). ▁Thus , ▁Marx ▁often ▁regarded ▁himself ▁as ▁perfect ing ▁a ▁theory ▁which ▁had ▁already ▁existed ▁for ▁a ▁long ▁time , ▁but ▁which ▁had ▁never ▁been ▁consist ently ▁presented ▁before . ▁ ▁Nevertheless , ▁in ▁the ▁Marx ist ▁tradition , ▁Marx ' s ▁theory ▁of ▁product - value ▁is ▁convention ally ▁l abeled ▁" the ▁labour ▁theory ▁of ▁value " — while ▁controvers y ▁pers ists ▁about ▁how ▁much ▁Marx ' s ▁theory ▁actually ▁diff ers ▁from ▁that ▁of ▁the ▁classical ▁political ▁econom ists . ▁ ▁Gold ▁refer ent ▁In ▁Das ▁Kap ital ▁Marx ▁normally ▁thinks ▁of ▁the ▁quantity ▁of ▁labour ▁that ▁determ ines ▁product - value ▁as ▁the ▁ratio ▁between ▁the ▁average ▁total ▁amount ▁of ▁labour - time ▁required ▁to ▁produce ▁a ▁reprodu cible ▁good , ▁and ▁the ▁corresponding ▁average ▁amount ▁of ▁labour ▁required ▁to ▁produce ▁a ▁unit ▁of ▁gold ▁( see ▁also ▁gold ▁standard ). ▁Al ready ▁in ▁ 1 8 4 4 , ▁long ▁before ▁he ▁wrote ▁Das ▁Kap ital , ▁Marx ▁was ▁very ▁aware ▁of ▁credit ▁money . ▁Where as ▁" com mod ity ▁money " ▁( co in age ▁or ▁b ull ion ) ▁played ▁an ▁important ▁role ▁in ▁the ▁earlier ▁stages ▁of ▁capital ist ▁development , ▁the ▁growth ▁of ▁integrated ▁capital ▁mark ets ▁meant ▁increased ▁use ▁of ▁credit ▁money . ▁Marx ▁felt ▁that ▁the ▁initial ▁assumption ▁of ▁gold - m oney ▁as ▁a ▁standard ▁of ▁value ▁was ▁just ified , ▁in ▁anal ys ing ▁the ▁capital ist