Itmaybequestionedwhetheritistruethatnosubstanceisrelative，asseemstobethecase，orwhetherexceptionistobemadeinthecaseofcertainsecondarysubstances。Withregardtoprimarysubstances，itisquitetruethatthereisnosuchpossibility，forneitherwholesnorpartsofprimarysubstancesarerelative。Theindividualmanoroxisnotdefinedwithreferencetosomethingexternal。Similarlywiththeparts：aparticularhandorheadisnotdefinedasaparticularhandorheadofaparticularperson，butasthehandorheadofaparticularperson。Itistruealso，forthemostpartatleast，inthecaseofsecondarysubstances；
thespecies\'man\'andthespecies\'ox\'arenotdefinedwithreferencetoanythingoutsidethemselves。Wood，again，isonlyrelativeinsofarasitissomeone\'sproperty，notinsofarasitiswood。Itisplain，then，thatinthecasesmentionedsubstanceisnotrelative。Butwithregardtosomesecondarysubstancesthereisadifferenceofopinion；thus，suchtermsas\'head\'and\'hand\'aredefinedwithreferencetothatofwhichthethingsindicatedareapart，andsoitcomesaboutthattheseappeartohavearelativecharacter。Indeed，ifourdefinitionofthatwhichisrelativewascomplete，itisverydifficult，ifnotimpossible，toprovethatnosubstanceisrelative。If，however，ourdefinitionwasnotcomplete，ifthosethingsonlyareproperlycalledrelativeinthecaseofwhichrelationtoanexternalobjectisanecessaryconditionofexistence，perhapssomeexplanationofthedilemmamaybefound。
Theformerdefinitiondoesindeedapplytoallrelatives，butthefactthatathingisexplainedwithreferencetosomethingelsedoesnotmakeitessentiallyrelative。
Fromthisitisplainthat，ifamandefinitelyapprehendsarelativething，hewillalsodefinitelyapprehendthattowhichitisrelative。Indeedthisisself-evident：forifamanknowsthatsomeparticularthingisrelative，assumingthatwecallthatarelativeinthecaseofwhichrelationtosomethingisanecessaryconditionofexistence，heknowsthatalsotowhichitisrelated。Forifhedoesnotknowatallthattowhichitisrelated，hewillnotknowwhetherornotitisrelative。Thisisclear，moreover，inparticularinstances。Ifamanknowsdefinitelythatsuchandsuchathingis\'double\'，hewillalsoforthwithknowdefinitelythatofwhichitisthedouble。Forifthereisnothingdefiniteofwhichheknowsittobethedouble，hedoesnotknowatallthatitisdouble。Again，ifheknowsthatathingismorebeautiful，itfollowsnecessarilythathewillforthwithdefinitelyknowthatalsothanwhichitismorebeautiful。Hewillnotmerelyknowindefinitelythatitismorebeautifulthansomethingwhichislessbeautiful，forthiswouldbesupposition，notknowledge。Forifhedoesnotknowdefinitelythatthanwhichitismorebeautiful，hecannolongerclaimtoknowdefinitelythatitismorebeautifulthansomethingelsewhichislessbeautiful：foritmightbethatnothingwaslessbeautiful。Itis，therefore，evidentthatifamanapprehendssomerelativethingdefinitely，henecessarilyknowsthatalsodefinitelytowhichitisrelated。
Nowthehead，thehand，andsuchthingsaresubstances，anditispossibletoknowtheiressentialcharacterdefinitely，butitdoesnotnecessarilyfollowthatweshouldknowthattowhichtheyarerelated。