whicharetheonlyconditionsspecified，andwhichheseemstoexplainnotastheconditionsbutastheproductofassociation。J。S。Millperceivedthatsomethingwaswantingwhichheafterwardstriedtosupply。Iwilljustindicateoneortwopoints，whichmayshowwhatproblemsthefatherbequeathedtothesonJamesMill，atoneplace，discussestheoddproblem’howithappensthatalltrainsofthoughtarenotthesame。’90Themoreobviousquestionis，onhishypothesis，howithappensthatanytwopeoplehavethesamebeliefs，sincethebeliefsaremadeofthemostvaryingmaterials。If，again，twoideaswhenassociatedremaindistinct，wehaveHume’sdifficulty。Whateverisdistinguishable，heargued，isseparable。
Iftwoideassimplyliesidebyside，asisapparentlyimpliedby’contiguity，’
sothateachcanbetakenapartwithoutchange，whyshouldwesupposethattheywillneverexistapart，or，indeed，thattheyshouldeveragaincometogether?Thecontiguitydoesnotdependuponthem，butuponsomeinscrutablecollocation，ofwhichwecanonlysaythatitexistsnow。ThisistheproblemwhichgreatlyoccupiedJ。S。Mill。
The’indissoluble’or’inseparable’
association，whichbecamethegrandarcanumoftheschool，whileintendedtoanswersomeofthesedifficulties，raisesothers。Millseemstoinsistuponsplittingaunitintopartsinorderthatitmaybeagainbroughttogetherbyassociation。SoJ。S。Mill，inanadmiringnote，confirmshisfather’sexplanation’oneofthemostimportantthoughtsinthewholetreatise’oftheinfinityofspace。91Wethinkspaceinfinitebecausewealways’associate’positionwithextension。Surelyspaceisextension；andtothinkofonewithouttheotherimpliesacontradiction。