AlthoughMill’sworkuponpurepoliticaleconomy，liesmainlybeyondmyprovince，itillustratesoneimportantpoint。Millspeaksasoneexpoundinganestablishedsystem。Thespeedwithwhichthebookwaswrittenshowsthatitdidnotimplyanyrevisionoffirstprinciples。MillisworkingingeneraluponRicardo’slines，inwhose’immortalPrinciples，’forexample，hefindsthefirstphilosophicalaccountofinternationaltrade。2*
Heassumestooeasilythatameremodificationofolddoctrinesisneeded，wherelaterwritershavedemandedathoroughgoingreconstruction。Hehasincurredsomeridicule，forexample，byanutterancecharacteristicofhisposition。Hesays，3*that’thereisnothinginthelawsofValuewhichremainsforthepresentoranyfuturewritertoclearup；thetheoryofthesubjectiscomplete。’Thephrasewasrash。Apparentlyunassailabletheorieshaveanuncomfortabletrickofsuddenlyexploding。Latereconomistsoftentakethisforacaseinpoint。
Theyhave，theythink，madeaspeciallysuccessfulbreachinthispartofMill’sdoctrine，andhisconfidencewassingularlyinfelicitous。Mill’slucklessboastwassuggestedbyhisrectificationofanambiguityintheterminologyofthescience。
How，heasked，couldtherebea’proportion’betweentwodisparatethings，a’quantity’supplyanda’desire’
demand？4*Heproceedstoremovetheambiguitybyanaccountofthe’equation’betweendemandandsupply，explainingtheprocessbywhichvaluesadjustthemselvessothatthequantitysuppliedatthecurrentpricewillbeequaltothequantitydemandedatthatprice。Itakeitthathisaccountofthefactsissubstantiallycorrect，andthat，byremovingcertaininconsistenciesoflanguage，hehadpurifiedthetheoryfromoneatoffallacies。Buthehimselfseemstoregardtheimprovementasmerelyoneofterminology。Hethinksthathispredecessorsmeanttostatethesamefacts，and，indeed，thattheymusthaveseenthetruth，thoughhecouldnotfindinthemanexpressstatement。WemayaskwhetherlaterimprovementsofMillhimselfamounttoasubstantialchangeinthetheory，ormerelytoabettermodeofexpression。Idonotdoubtthatmoderneconomistshavemuchimprovedthelanguageinwhichthetheoryisexpressed。