TocarryoutthistheoryisthecentralaimofHamilton’s’NaturalRealism。’Reid’sstatementmightseemtobenotablunder，butatruism。’Iamconsciousoftherose’meansprecisely’IhavecertainsensationswhichIregardasimplyingtheexistenceofapermanentexternalreality。’Butthisistointerpretperceptionasinvolvingan’inference，’andtherefore，accordingtoHamilton，istoabandontheessentialdoctrineofNaturalRealism。29*Itmayseemstrange，headmits，butitistrue，’thatthesimpleandprimaryactofintelligenceshouldbeajudgment，whichphilosophersingeneralhavereceivedasacompoundandderivativeoperation。’30*’Knowing’and’knowingthatweknow’arethesamething；asconceivingthesidesandanglesofatrianglearethesameprocess，distinguishableinthought，but’innature，oneandindivisible。’31*What，then，isthisessentialjudgment？Inanactofsensibleperception，saysHamilton，Iamconsciousofmyselfandofsomethingdifferentfrommyself。32*Thismightseemtodefinethedistinctionbetween’consciousness’and’perception。’theobjectofmythoughtmay，asHamiltonremarks，bea’modeofmind’aswellasa’modeofmatter。’33*Consciousnessofself，weshouldinfer，differsfromconsciousnessofthenot-self，anditisjustthepresenceofthenot-selfwhichdistinguishesperceptionfromsimpleconsciousness。Hamilton，however，arguesthatperceptionissimpleconsciousness；orthatthedistinction，forhispurpose，isirrelevant。Thereisa’logical’butnota’psychological’difference。34*Everyactofconsciousnessimpliesaconceptionoftheego。But’thescienceofoppositesisone。’thereforeconsciousnessoftheegoinvolvesconsciousnessofthenon-ego，or，inthesimplestpossibleactofintelligenceImustbetakentoaffirmtheexistencebothofanegoandanon-ego。
IfIcannoteventhinkaboutmyselfwithoutaffirmingtheexistenceofanexternalworld，itwouldbesuperfluoustolookaboutforfurtherproofsofitsexistence。Buthereoccursasingulardifficulty。Hamiltonhastoguardagainstthetranscendentalistaswellasagainstthesceptic。Heisthereforenotonlya’realist，’butwithequalemphasisa’relativist。’
thatourknowledgeisessentiallyrelativeisoneofthepointsuponwhichheinsistsmostemphatically，andconfirmsasusualbyacatenaofauthorities。Itis，hesays，thetruth’mostharmoniouslyre-echoedbyeveryphilosopherofeveryschool，exceptthemodernGermans。’35*Thephraserelativityhasmorethanonemeaning；butaccordingtoHamiltonmeansatleastthis：
’ourwholeknowledgeofmindandmatterisrelative——
conditioned——relativelyconditioned。’Ofmindandmatter’inthemselves’weonlyknowthattheyare’incognisable。’’Allthatweknowisthereforephenomenal——phenomenaloftheunknown。’
This，then，isacardinaldoctrine。HowisitcompatiblewiththeDoctrinethattheegoandnon-egoaregivenineveryactofconsciousness？Mindandmatter，aswehaveseen，areseparated’bythewholediameterofbeing。’theyexpress’twoseriesofphenomena，knownless’？not’inthemselvesthan’？but，incontradistinctionfromeachother。’36*Whatisgivenisnottwofacts，theegoandthenon-ego，butthe’relation。’Somehow，theconsciousactimpliesthepresenceoftwofactors，unknowableinthemselves。The’scienceofopposites’maybe’thesame，’but，ifIknowneitheropposite，therecanbeverylittlescience。
Strangely，Hamiltonseemstoconfusethedifferencebetweenknowingarelationandknowingthetwothingsrelated。Hetellsusasaroughillustration，thatifweconsidertheperceptionofabooktobemadeupoftwelveparts，fourmaybegivenbythebook，fourbythesight，andfourby’allthatintervenes。’37*
Heinfers，presently，thatthe’greatproblemofphilosophy’isto’distinguishwhatelementsarecontributedbytheknowingsubject，whatelementsbytheobjectknown。’38*Betweenthesestatementswehavearenewedandemphaticassertionofthe’relativityofknowledge。’Hamilton，thatis，speaksasiffromthefactthatlifesupposesbreathingwecouldinferhowfarlifedependsuponthelungsandhowfarupontheair。Fromarelationbetweentwothings，unknowableinthemselves，wecansurelylearnnothingastothethingsseparately。Equalityoftwoquantitiesiscompatiblewithindefinitevariationintheequalquantities。39*Thedifficultyisincreasedwhenweaskhowthelineisactuallydrawn。ThedistinctionbetweensubjectiveandobjectivecorrespondstothedistinctionbetweentheprimaryandsecondaryqualitiesofwhichBerkeleyhaddeniedthevalidity。
Both，heheld，areonthesameplane，andexistonly’inourminds。’Hamiltonholdsthattheso-called’secondaryqualities’
areonly’subjectiveaffections。’TheyarenotproperlyqualitiesofBodyatall，butsensationsproducedinthemindbytheactionofbodiesonthenervoussystem。40*Theopinionthatthesesecondaryqualitiesbelongtothenon-egoisthe’vulgarorundevelopedformofnaturalrealism。’Hence，whenwesaythatweareconsciousofthe’rose’orthe’inkstand，’weoughttoregardthecolour，fragrance，temperature，andsoon，asaffectionsoftheego。Tothenon-egobelongtheprimaryqualitiesalone；andthesearesubstantiallynothingbutextensionandsolidity。41*
Inotherwords，therosebelongstothenon-egoasspace-filling；
totheego，ascolouredandfragrant。Uponthis，itiseasytoremarkwithMill，thatasthevulgaradmittedlyconsiderthewholerosetobelongtothenon-ego，andthedistinctiontohavebeenfirstdrawnbyphilosophers，weatonceadmitanillusioninwhat，OnHamilton’sprinciples，isapparentlya’deliveranceofconsciousness。’Whyareweforbiddentomakethesamehypothesisastotheprimaryqualities？’Falsusinuno，’asHamiltonsomewheresays，’falsusinomnibus。’Ifmyjudgmentofcolourbeillusory，whynotmyjudgmentofextension？TheveracityoftheCreatorisequallyconcernedinbothcases。
But，inthenextplace，wenowreachamoreseriousdifficulty。Thenon-ego，wesee，correspondssimplytothequalitiesfullyassignableintermsofspace。ButHamiltonhasreadKant，andmoreoverbeenconvincedbyhim。Kanthasprovedbeyond’thepossibilityofdoubt，’42*thetruththatspaceisa’fundamentalcondition’ofthought，andthereforebelongstotheego。Thisatoncethrowsusbackintoidealism。Thewholerosehasbecomeathought，notathing。Solongasheroundlyassertsthatmindperceivesmatter，thatmattermeanssolidspace，andthatthistruthisimpliedbytheverysimplestactofintelligence，wemaywonderathisaudacity，butwemayadmithisconsistency。Buttocombinethiswiththemostpositiveassertionsofthe’relativity’ofknowledge，thatis，ofourinabilitytoknoweithermindormatter，andthentoacceptasconclusiveKant’stheorythatspaceisamentalform，istolandusinahopelesslyinconsistentposition。WhatKantpreciselymeant，orwhetherhehadnotvariousandinconsistentmeanings，ishappilyaquestionbeyondmypurpose。Hamilton’sviewofKantisclear。’Thedistinctivepeculiarity’ofKant’sdoctrine，hesays，is’itsspecialdemonstrationoftheabsolutesubjectivityofspace，andingeneralofprimaryattributesofmatter。’43*
HearguesthatifReidvirtuallyheldthesameview，heabandonedtheprincipleofNaturalRealism。44*If，then，Kant’stheorywasconclusivelyproved，wasnotHamiltonboundtogiveuphisessentialprinciple？Hetellsusthattheprimaryqualitiesare’unambiguouslyobjectiveobject-objects，’whereasthesecondaryare’unambiguouslysubjectivesubject-objects。’45*Yet，headmitsthatKantprovestheprimarytobeabsolutelysubjective，’Ihavefrequentlyasserted，’hesaysagain，thatin’perceptionweareconsciousoftheexternalobjectimmediatelyandinitself。ThisisthedoctrineofNaturalRealism。’Butheexplainsthatbyspeakingofathing’knowninitself’hedoesnotmeanknown’outofrelationtous，’butknown’asthenecessarycorrelativeofaninternalqualityofwhichIamconscious。’46*
Thatis，apparently，knowingathing’initself’isknowingit’notinitself，’butonlyinitseffect；whichagainistoabandon’NaturalRealism。’Hamiltonfindsawayoutoftheseapparentcontradictionswhichsatisfieshimself。Boththeories，hesuggests，maybetrue。Wehaveclearlyanaprioriknowledgeofspace’consideredasaformorfundamentallawofthought，’
butalsoanempiricalknowledgeofwhat，inthisrelation，maybecalled’extension。’47*Heagrees，hesays，withKantthatan’aprioriimagination’ofspaceisa’necessaryconditionofthepossibilityofthought’；butdiffersfromKantbyholdingthatwehavean’aposterioripercept’ofspace’ascontingentlyapprehendedinthisorthatactualcomplexusofassociations。’48*ItismostnaturaltointerpretthisasavirtualacceptanceofKant’sdoctrine。Itfallsinwithwhathesayselsewhere：’thenotionofspaceisapriori，thenotionofwhatspacecontains，adventitiousoraposteriori。OfthislatterclassisthatofBodyorMatter。’49*IfImerelyfillupspacebythesenseofresistance，ashethinks，thatisasubordinateoperation，innowayaffectingthesubjectivecharacterofspacegenerally。If，ontheotherhand，Icanacquireanempiricalnotionofspaceindependently，itseemsimpossibletoseewhyI
shouldadmittheapriorinotion。Hamiltonstartsfromtheassertionthatweactuallyperceivefacts，andcomestoadmitthatwesimplyorganisesensations。50*
Finally，Hamiltonturnstoyetanothertheory。Hisessentialpointisthenecessityofbelievingconsciousness。Whenweinquirewhatisthespherewithinwhichconsciousnessisinfallible，wehavetoacceptsomethingverylikethecondemned’crotchet’oftheCosmotheticIdealists。Theinfallibilityofconsciousnesshas，afterall，tobelimited。Thesummaryassertionthatthemindcanleapthegulfwhichseparatesitfrommatterinsistsuponsomeexplanation。Consciousnessisinfalliblewhenitisitsownobject。Butitisplain，asHamiltonagrees，thatthisprimary，direct，orpresentativeknowledgeisonly，asitwere，thelimitingcaseofknowledge。AccordinglyhecondemnsReidforspeakingofmemoryasan’immediateknowledgeofthepast。’51*The’object’inthiscaseisnotthepastevent，butsomepictureofthepastevent；notinhisillustrationGeorgeIVlandingatLeith，butamentalimageofthelanding，’includingaconviction’thatitsomehowrepresentsapastreality。Itisnatural，then，toinquirewhethermybeliefinanexternalworldmaynotbeaconsciousnessofamodificationofmyself，includingaconvictionthatitmerely’represents’anexternalworld，52*andisnotindirectcontactwiththe’non-ego。’Immediateknowledgeofthepastis’acontradictioninterms。’Andthis，headds，appliesequallytoan’immediateknowledgeofthedistant。’53*ItisfalsetosaywithReidthattenmenallseethesamesun。Eachseesadifferentobject，becauseeachseesadifferentatofraysfromwhichheinferstheobject。54*Weperceiveonlymodificationsoflight，or，ashehassaidbefore，the’raysoflightinrelationtoandincontactwiththeretina。’55*Thereis，asheadds，nogreatermarvelinourperceptionoftheexternalworldthanintheadmittedfactthatmindisconnectedwithbody。Therefore，inhisfinalstatement，56*itislaiddownasanessentialprinciplethatconsciousnessisa’knowledgesolelyofwhatisnowandherepresenttothemind。’Whatismeantbythe’here’？’Itistheconditionofintuitiveperception，’hesays，thatasensationisactuallyfelt’therewhereitisfelttobe。’Tosupposethatapaininthetoeisfeltreallyin’thebrainisconformableonlytoatheoryofrepresentationism。’57*Ifthemindisnotitselfextendedorinanywayasubjectofspace-relations，doesthisnotimplythatthewholeexternalworldissomehowoutsidethesphereofimmediateknowledge——aconstruction，notamodeofconsciousness？TothisHamiltonrepliesthatthe’nervousorganism……incontrasttoallexteriortoitself，appertainstotheconcretehumanego，andisinthisrespectsubjective，internal；whereasincontrasttotheabstract，immaterialego，thepuremind，itbelongstothenon-ego，andinthisrespectisobjective，external。’58*Thisviewleadshimintopurephysiology。Heaskswhetherthemindisconsciousofsensationsattheperipheryofthenerves，orata’centralextremityinanextendedsensoriumcommune。’Hedeclares，lestsuchlanguagemayappearsuspicious，thatthequestionofmaterialismisnotraisedbythisassumption。59*Anyhow，sincethebodyisnowinsomesensepartoftheconcretehumanego，ourconsciousnessoftheprimaryqualitiesisinthissensepartofourconsciousnessofourselves。Theyaregivenasexistinginourownorganism，or，inotherwords，asweoccupyspace，wehavean’immediate’knowledgeofspace。60*Ionlynotethepeculiarinterpretationnowputuponthedeliveranceofconsciousness。Ifancymyselftoperceivethesun；whatIreally’perceive’istheactionofraysoflightonmyretina。YetitisobviousthatIonlylearnoftheexistenceof’rays’or’retina’longaftertheperception。