▁its ▁production . ▁This ▁value ▁was ▁inher ently ▁real . ▁ ▁Mon et ary ▁( nom inal ) ▁values ▁ ▁Econom ic ▁values ▁can ▁always ▁be ▁expressed ▁in ▁mon et ary ▁terms ▁except ▁in ▁a ▁bar ter ▁economy . ▁There ▁are ▁two ▁reasons ▁to ▁avoid ▁doing ▁so . ▁The ▁first ▁is ▁in ▁order ▁to ▁make ▁compar isons ▁of ▁wealth ▁between ▁different ▁periods ▁or ▁curr encies . ▁The ▁second ▁is ▁that ▁in ▁many ▁simple ▁models ▁all ▁prices ▁will ▁move ▁together ▁– ▁for ▁instance ▁in ▁perfect ▁competition ▁the ▁effect ▁of ▁a ▁change ▁in ▁money ▁supply ▁may ▁be ▁a ▁proportional ▁change ▁in ▁all ▁prices . ▁In ▁the ▁latter ▁case ▁it ▁is ▁easier ▁to ▁work ▁with ▁a ▁single ▁variable ▁den oting ▁price ▁level ▁than ▁with ▁a ▁vector ▁of ▁prices ; ▁and ▁real ▁values ▁are ▁then ▁automatically ▁available ▁as ▁money ▁values ▁divided ▁by ▁the ▁common ▁price ▁level . ▁ ▁Real ▁values ▁ ▁The ▁use ▁of ▁real ▁values ▁beyond ▁the ▁conf ines ▁of ▁simple ▁models ▁re lies ▁on ▁price ▁indexes ▁derived ▁from ▁b ask ets ▁of ▁goods . ▁A ▁comp lication ▁ar ises ▁if ▁values ▁defined ▁this ▁way ▁are ▁used ▁in ▁an ▁economic ▁model , ▁which ▁is ▁that ▁the ▁model ▁may ▁treat ▁w ages ▁differently ▁from ▁prices . ▁If ▁services ▁( which ▁may ▁sometimes ▁amount ▁to ▁direct ▁payment ▁for ▁labour ) ▁are ▁included ▁in ▁the ▁index , ▁care ▁needs ▁to ▁be ▁taken ▁to ▁avoid ▁confusion . ▁ ▁Whe at ▁values ▁ ▁P ig ou , ▁in ▁his ▁paper ▁on ▁the ▁value ▁of ▁money , ▁used ▁whe at ▁values ,