Thoughtherealvalueofacornrent，itistobeobserved，however，variesmuchlessfromcenturytocenturythanthatofamoneyrent，itvariesmuchmorefromyeartoyear。Themoneypriceoflabour，asIshallendeavourtoshowhereafter，doesnotfluctuatefromyeartoyearwiththemoneypriceofcorn，butseemstobeeverywhereaccommodated，nottothetemporaryoroccasional，buttotheaverageorordinarypriceofthatnecessaryoflife。Theaverageorordinarypriceofcornagainisregulated，asIshalllikewiseendeavourtoshowhereafter，bythevalueofsilver，bytherichnessorbarrennessofthemineswhichsupplythemarketwiththatmetal，orbythequantityoflabourwhichmustbeemployed，andconsequentlyofcornwhichmustbeconsumed，inordertobringanyparticularquantityofsilverfromtheminetothemarket。Butthevalueofsilver，thoughitsometimesvariesgreatlyfromcenturytocentury，seldomvariesmuchfromyeartoyear，butfrequentlycontinuesthesame，orverynearlythesame，forhalfacenturyoracenturytogether。Theordinaryoraveragemoneypriceofcorn，therefore，may，duringsolongaperiod，continuethesameorverynearlythesametoo，andalongwithitthemoneypriceoflabour，provided，atleast，thesocietycontinues，inotherrespects，inthesameornearlyinthesamecondition。Inthemeantimethetemporaryandoccasionalpriceofcornmayfrequentlybedouble，oneyear，ofwhatithadbeentheyearbefore，orfluctuate，forexample，fromfiveandtwentytofiftyshillingsthequarter。Butwhencornisatthelatterprice，notonlythenominal，buttherealvalueofacornrentwillbedoubleofwhatitiswhenattheformer，orwillcommanddoublethequantityeitheroflabourorofthegreaterpartofothercommodities;themoneypriceoflabour，andalongwithitthatofmostotherthings，continuingthesameduringallthesefluctuations。
Labour，therefore，itappearsevidently，istheonlyuniversal，aswellastheonlyaccuratemeasureofvalue，ortheonlystandardbywhichwecancomparethevaluesofdifferentcommoditiesatalltimes，andatallplaces。Wecannotestimate，itisallowed，therealvalueofdifferentcommoditiesfromcenturytocenturybythequantitiesofsilverwhichweregivenforthem。Wecannotestimateitfromyeartoyearbythequantitiesofcorn。Bythequantitiesoflabourwecan，withthegreatestaccuracy，estimateitbothfromcenturytocenturyandfromyeartoyear。Fromcenturytocentury，cornisabettermeasurethansilver，because，fromcenturytocentury，equalquantitiesofcornwillcommandthesamequantityoflabourmorenearlythanequalquantitiesofsilver。Fromyeartoyear，onthecontrary，silverisabettermeasurethancorn，becauseequalquantitiesofitwillmorenearlycommandthesamequantityoflabour。
Butthoughinestablishingperpetualrents，oreveninlettingverylongleases，itmaybeofusetodistinguishbetweenrealandnominalprice;itisofnoneinbuyingandselling，themorecommonandordinarytransactionsofhumanlife。
Atthesametimeandplacetherealandthenominalpriceofallcommoditiesareexactlyinproportiontooneanother。Themoreorlessmoneyyougetforanycommodity，intheLondonmarketforexample，themoreorlesslabouritwillatthattimeandplaceenableyoutopurchaseorcommand。Atthesametimeandplace，therefore，moneyistheexactmeasureoftherealexchangeablevalueofallcommodities。Itisso，however，atthesametimeandplaceonly。
Thoughatdistantplaces，thereisnoregularproportionbetweentherealandthemoneypriceofcommodities，yetthemerchantwhocarriesgoodsfromtheonetotheotherhasnothingtoconsiderbuttheirmoneyprice，orthedifferencebetweenthequantityofsilverforwhichhebuysthem，andthatforwhichheislikelytosellthem。HalfanounceofsilveratCantoninChinamaycommandagreaterquantitybothoflabourandofthenecessariesandconveniencesoflifethananounceatLondon。A