Anactioniscalledanact—ormoraldeed—insofarasitissubjecttolawsofobligation，andconsequentlyinsofarasthesubjectofitisregardedwithreferencetothefreedomofhischoiceintheexerciseofhiswill。Theagent—astheactorordoerofthedeed—isregardedas，throughtheact，theauthorofitseffect;
andthiseffect，alongwiththeactionitself，maybeimputedtohim，ifbepreviouslyknewthelawinvirtueofwhichanobligationresteduponhim。
Apersonisasubjectwhoiscapableofhavinghisactionsimputedtohim。Moralpersonalityis，therefore，nothingbutthefreedomofarationalbeingundermorallaws;anditistobedistinguishedfrompsychologicalfreedomasthemerefacultybywhichwebecomeconsciousofourselvesindifferentstatesoftheidentityofourexistence。Henceitfollowsthatapersonisproperlysubjecttonootherlawsthanthosehelaysdownforhimself，eitheraloneorinconjunctionwithothers。
Athingiswhatisincapableofbeingthesubjectofimputation。
Everyobjectofthefreeactivityofthewill，whichisitselfvoidoffreedom，isthereforecalledathing（rescorporealis）。
Rightorwrongapplies，asageneralquality，toanact（rectumautminusrectum），insofarasitisinaccordancewithdutyorcontrarytoduty（factumlicitumautillicitum），nomatterwhatmaybethesubjectororiginofthedutyitself。Anactthatiscontrarytodutyiscalledatransgression（reatus）。
Anunintentionaltransgressionofaduty，whichis，nevertheless，imputabletoaperson，iscalledamerefault（culpa）。Anintentionaltransgression—thatis，anactaccompaniedwiththeconsciousnessthatitisatransgression—constitutesacrime（dolus）。
Whateverisjuridicallyinaccordancewithexternallawsissaidtobejust（jus，instum）;andwhateverisnotjuridicallyinaccordancewithexternallawsisunjust（unjustum）。
Acollisionofdutiesorobligations（collisioofficiorums。
obligationum）wouldbetheresultofsucharelationbetweenthemthattheonewouldannultheother，inwholeorinpart。Dutyandobligation，however，areconceptionswhichexpresstheobjectivepracticalnecessityofcertainactions，andtwooppositerulescannotbeobjectiveandnecessaryatthesametime;forifitisadutytoactaccordingtooneofthem，itisnotonlynodutytoactaccordingtoanoppositerule，buttodosowouldevenbecontrarytoduty。Henceacollisionofdutiesandobligationsisentirelyinconceivable（obligationesnoncolliduntur）。Theremay，however，betwogroundsofobligation（rationesobligandi），connectedwithanindividualunderaruleprescribedforhimself，andyetneithertheonenortheothermaybesufficienttoconstituteanactualobligation（rationesobligandinonobligantes）;andinthatcasetheoneofthemisnotaduty。Iftwosuchgroundsofobligationareactuallyincollisionwitheachother，practicalphilosophydoesnotsaythatthestrongerobligationistokeeptheupperhand（fortiorobligatiovincit），butthatthestrongergroundofobligationistomaintainitsplace（fortiorobligandiratiovincit）。
ObligatoryLawsforwhichanexternallegislationispossiblearecalledgenerallyexternallaws。Thoseexternallaws，theobligatorinessofwhichcanberecognisedbyreasonapriorievenwithoutanexternallegislation，arecallednaturallaws。Thoselaws，again，whicharenotobligatorywithoutactualexternallegislation，arecalledpositivelaws。Anexternallegislation，containingpurenaturallaws，isthereforeconceivable;butinthatcaseapreviousnaturallawmustbepresupposedtoestablishtheauthorityofthelawgiverbytherighttosubjectotherstoobligationthroughhisownactofwill。
Theprinciplewhichmakesacertainactionadutyisapracticallaw。Theruleoftheagentoractor，whichheformsasaprincipleforhimselfonsubjectivegrounds，iscalledhismaxim。Hence，evenwhenthelawisoneandinvariable，themaximsoftheagentmayyetbeverydifferent。
Thecategoricalimperativeonlyexpressesgenerallywhatconstitutesobligation。Itmayberenderedbythefollowingformula:\"Actaccordingtoamaximwhichcanbeadoptedatthesametimeasauniversallaw。\"Actionsmustthereforebeconsidered，inthefirstplace，accordingtotheirsubjectiveprinciple;butwhetherthisprincipleisalsovalidobjectivelycanonlybeknownbythecriterionofthecategoricalimperative。Forreasonbringstheprincipleormaximofanyactiontothetest，bycallingupontheagenttothinkofhimselfinconnectionwithitasatthesametimelayingdownauniversallaw，andtoconsiderwhetherhisactionissoqualifiedastobefitforenteringintosuchauniversallegislation。
Thesimplicityofthislaw，incomparisonwiththegreatandmanifoldconsequenceswhichmaybedrawnfromit，aswellasitscommandingauthorityandsupremacywithouttheaccompanimentofanyvisiblemotiveorsanction，mustcertainlyatfirstappearverysurprising。Andwemaywellwonderatthepowerofourreasontodeterminetheactivityofthewillbythemereideaofthequalificationofamaximfortheuniversalityofapracticallaw，especiallywhenwearetaughttherebythatthispracticalmorallawfirstrevealsapropertyofthewillwhichthespeculativereasonwouldneverhavecomeuponeitherbyprinciplesapriori，orfromanyexperiencewhatever;andevenifithadascertainedthefact，itcouldneverhavetheoreticallyestablisheditspossibility。Thispracticallaw，however，notonlydiscoversthefactofthatpropertyofthewill，whichisfreedom，butirrefutablyestablishesit。Henceitwillbelesssurprisingtofindthatthemorallawsareundemonstrable，andyetapodeictic，likethemathematicalpostulates;andthatthey，atthesametime，openupbeforeusawholefieldofpracticalknowledge，fromwhichreason，onitstheoreticalside，mustfinditselfentirelyexcludedwithitsspeculativeideaoffreedomandallsuchideasofthesupersensiblegenerally。
Theconformityofanactiontothelawofdutyconstitutesitslegality;theconformityofthemaximoftheactionwiththelawconstitutesitsmorality。Amaximisthusasubjectiveprincipleofaction，whichtheindividualmakesaruleforhimselfastohowinfacthewillact。
Ontheotherhand，theprincipleofdutyiswhatreasonabsolutely，andthereforeobjectivelyanduniversally，laysdownintheformofacommandtotheindividual，astohowheoughttoact。
Thesupremeprincipleofthescienceofmoralsaccordinglyisthis:\"Actaccordingtoamaximwhichcanlikewisebevalidasauniversallaw。\"EverymaximwhichisnotqualifiedaccordingtothisconditioniscontrarytoMorality。
Lawsarisefromthewill，viewedgenerallyaspracticalreason;
maximsspringfromtheactivityofthewillintheprocessofchoice。Thelatterinmaniswhatconstitutesfree—will。Thewillwhichreferstonothingelsethanmerelawcanneitherbecalledfreenornotfree，becauseitdoesnotrelatetoactionsimmediately，buttothegivingofalawforthemaximofactions;itisthereforethepracticalreasonitself。Henceasafaculty，itisabsolutelynecessaryinitself，andisnotsubjecttoanyexternalnecessitation。Itis，therefore，onlytheactofchoiceinthevoluntaryprocessthatcanbecalledfree。