butinordertoansweritwerequireawholelogicalandpsychologicalapparatus。
Benthamshowsthisapparatusatwork，butdoesnotexpounditsorigininanyseparatetreatise。Enoughinformation，however，isgivenastohismethodinthecuriouscollectionofthefragmentsconnectedwiththeChrestomathia。
Alogicalmethoduponwhichheconstantlyinsistedisthatof’bipartition，’16*
calledalsothe’dichotomous’or’bifurcate’method，andexemplifiedbythestalled’PorphyrianTree。’Theprincipleis，ofcourse，simple。Takeanygenus：divideitintotwoclasses，oneofwhichhasandtheotherhasnotacertainmark。Thetwoclassesmustbemutuallyexclusiveandtogetherexhaustive。
Repeattheoperationuponeachoftheclassesandcontinuetheprocessaslongasdesired。17*Ateverystepyouthushaveacompleteenumerationofallthespecies，varieties，andsoon，eachofwhichexcludesalltheothers。Nomerelogic，indeed，cansecuretheaccuracyandstilllesstheutilityoftheprocedure。Thedifferencesmaybeinthemselvesambiguousorirrelevant。IfIclassifyplantsas’trees’and’nottrees，’thelogicalformissatisfied：butIhavestilltoaskwhether’tree’conveysadeterminatemeaning，andwhetherthedistinctioncorrespondstoadifferenceofanyimportance。