tself。　If　so；　we　ought　to　do　this　in　the　first　case。　　　This　presents　a　difficulty：　if　to　perceive　by　sight　is　just　to　see；　and　what　is　seen　is　colour　（or　the　coloured）；　then　if　we　are　to　see　that　which　sees；　that　which　sees　originally　must　be　coloured。　It　is　clear　therefore　that　'to　perceive　by　sight'　has　more　than　one　meaning；　for　even　when　we　are　not　seeing；　it　is　by　sight　that　we　discriminate　darkness　from　light；　though　not　in　the　same　way　as　we　distinguish　one　colour　from　another。　Further；　in　a　sense　even　that　which　sees　is　coloured；　for　in　each　case　the　sense…organ　is　capable　of　receiving　the　sensible　object　without　its　matter。　That　is　why　even　when　the　sensible　objects　are　gone　the　sensings　and　imaginings　continue　to　exist　in　the　sense…organs。　　　The　activity　of　the　sensible　object　and　that　of　the　percipient　sense　is　one　and　the　same　activity；　and　yet　the　distinction　between　their　being　remains。　Take　as　illustration　actual　sound　and　actual　hearing：　a　man　may　have　hearing　and　yet　not　be　hearing；　and　that　which　has　a　sound　is　not　always　sounding。　But　when　that　which　can　hear　is　actively　hearing　and　which　can　sound　is　sounding；　then　the　actual　hearing　and　the　actual　sound　are　merged　in　one　（these　one　might　call　respectively　hearkening　and　sounding）。　　　If　it　is　true　that　the　movement；　both　the　acting　and　the　being　acted　upon；　is　to　be　found　in　that　which　is　acted　upon；　both　the　sound　and　the　hearing　so　far　as　it　is　actual　must　be　found　in　that　which　has　the　faculty　of　hearing；　for　it　is　in　the　passive　factor　that　the　actuality　of　the　active　or　motive　factor　is　realized；　that　is　why　that　which　causes　movement　may　be　at　rest。　Now　the　actuality　of　that　which　can　sound　is　just　sound　or　sounding；　and　the　actuality　of　that　which　can　hear　is　hearing　or　hearkening；　'sound'　and　'hearing'　are　both　ambiguous。　The　same　account　applies　to　the　other　senses　and　their　objects。　For　as　the…acting…and…being…acted…upon　is　to　be　found　in　the　passive；　not　in　the　active　factor；　so　also　the　actuality　of　the　sensible　object　and　that　of　the　sensitive　subject　are　both　realized　in　the　latter。　But　while　in　some　cases　each　aspect　of　the　total　actuality　has　a　distinct　name；　e。g。　sounding　and　hearkening；　in　some　one　or　other　is　nameless；　e。g。　the　actuality　of　sight　is　called　seeing；　but　the　actuality　of　colour　has　no　name：　the　actuality　of　the　faculty　of　taste　is　called　tasting；　but　the　actuality　of　flavour　has　no　name。　Since　the　actualities　of　the　sensible　object　and　of　the　sensitive　faculty　are　one　actuality　in　spite　of　the　difference　between　their　modes　of　being；　actual　hearing　and　actual　sounding　appear　and　disappear　from　existence　at　one　and　the　same　moment；　and　so　actual　savour　and　actual　tasting；　&c。；　while　as　potentialities　one　of　them　may　exist　without　the　other。　The　earlier　students　of　nature　were　mistaken　in　their　view　that　without　sight　there　was　no　white　or　black；　without　taste　no　savour。　This　statement　of　theirs　is　partly　true；　partly　false：　'sense'　and　'the　sensible　object'　are　ambiguous　terms；　i。e。　may　denote　either　potentialities　or　actualities：　the　statement　is　true　of　the　latter；　false　of　the　former。　This　ambiguity　they　wholly　failed　to　notice。　　　If　voice　always　implies　a　concord；　and　if　the　voice　and　the　hearing　of　it　are　in　one　sense　one　and　the　same；　and　if　concord　always　implies　a　ratio；　hearing　as　well　as　what　is　heard　must　be　a　ratio。　That　is　why　the　excess　of　either　the　sharp　or　the　flat　destroys　the　hearing。　（So　also　in　the　case　of　savours　excess　destroys　the　sense　of　taste；　and　in　the　case　of　colours　excessive　brightness　or　darkness　destroys　the　sight；　and　in　the　case　of　smell　excess　of　strength　whether　in　the　direction　of　sweetness　or　bitterness　is　destructive。）　This　shows　that　the　sense　is　a　ratio。　　　That　is　also　why　the　objects　of　sense　are　（1）　pleasant　when　the　sensible　extremes　such　as　acid　or　sweet　or　salt　being　pure　and　unmixed　are　brought　into　the　proper　ratio；　then　they　are　pleasant：　and　in　general　what　is　blended　is　more　pleasant　than　the　sharp　or　the　flat　alone；　or；　to　touch；　that　which　is　capable　of　being　either　warmed　or　chilled：　the　sense　and　the　ratio　are　identical：　while　（2）　in　excess　the　sensible　extremes　are　painful　or　destructive。　　　Each　sense　then　is　relative　to　its　particular　group　of　sensible　qualities：　it　is　found　in　a　sense…organ　as　such　and　discriminates　the　differences　which　exist　within　that　group；　e。g。　sight　discriminates　white　and　black；　taste　sweet　and　bitter；　and　so　in　all　cases。　Since　we　also　discriminate　white　from　sweet；　and　indeed　each　sensible　quality　from　every　other；　with　what　do　we　perceive　that　they　are　different？　It　must　be　by　sense；　for　what　is　before　us　is　sensible　objects。　（Hence　it　is　also　obvious　that　the　flesh　cannot　be　the　ultimate　sense…organ：　if　it　were；　the　discriminating　power　could　not　do　its　work　without　immediate　contact　with　the　object。）　　　Therefore　（1）　discrimination　between　white　and　sweet　cannot　be　effected　by　two　agencies　which　remain　separate；　both　the　qualities　discriminated　must　be　present　to　something　that　is　one　and　single。　On　any　other　supposition　even　if　I　perceived　sweet　and　you　perceived　white；　the　difference　between　them　would　be　apparent。　What　says　that　two　things　are　different　must　be　one；　for　sweet　is　different　from　white。　Therefore　what　asserts　this　difference　must　be　self…identical；　and　as　what　asserts；　so　also　what　thinks　or　perceives。　That　it　is　not　possible　by　means　of　two　agencies　which　remain　separate　to　discriminate　two　objects　which　are　separate；　is　therefore　obvious；　and　that　（it　is　not　possible　to　do　this　in　separate　movements　of　time　may　be　seen'　if　we　look　at　it　as　follows。　For　as　what　asserts　the　difference　between　the　good　and　the　bad　is　one　and　the　same；　so　also　the　time　at　which　it　asserts　the　one　to　be　different　and　the　other　to　be　different　is　not　accidental　to　the　assertion　（as　it　is　for　instance　when　I　now　assert　a　difference　but　do　not　assert　that　there　is　now　a　difference）；　it　asserts　thus…both　now　and　that　the　objects　are　different　now；　the　objects　therefore　must　be　present　at　one　and　the　same　moment。　Both　the　discriminating　power　and　the　time　of　its　exercise　must　be　one　and　undivided。　　　But；　it　may　be　objected；　it　is　impossible　that　what　is　self…identical　should　be　moved　at　me　and　the　same　time　with　contrary　movements　in　so　far　as　it　is　undivided；　and　in　an　undivided　moment　of　time。　For　if　what　is　sweet　be　the　quality　perceived；　it　moves　the　sense　or　thought　in　this　determinate　way；　while　what　is　bitter　moves　it　in　a　contrary　way；　and　what　is　white　in　a　different　way。　Is　it　the　case　then　that　what　discriminates；　though　both　numerically　one　and　indivisible；　is　at　the　same　time　divided　in　its　being？　In　one　sense；　it　is　what　is　divided　that　perceives　two　separate　objects　at　once；　but　in　another　sense　it　does　so　qua　undivided；　for　it　is　divisible　in　its　being　but　spatially　and　numerically　undivided。　is　not　this　impossible？　For　while　it　is　true　that　what　is　self…identical　and　undivided　may　be　both　contraries　at　once　potentially；　it　cannot　be　self…identical　in　its　being…it　must　lose　its　unity　by　being　put　into　activity。　It　is　not　possible　to　be　at　once　white　and　black；　and　therefore　it　must　also　be　impossible　for　a　thing　to　be　affected　at　one　and　the　same　moment　by　the　forms　of　both；　assuming　it　to　be　the　case　that　sensation　and　thinking　are　properly　so　described。　　　The　answer　is　that　just　as　what　is　called　a　'point'　is；　as　being　at　once　one　and　two；　properly　said　to　be　divisible；　so　here；　that　which　discriminates　is　qua　undivided　one；　and　active　in　a　single　moment　of　time；　while　so　far　forth　as　it　is　divisible　it　twice　over　uses　the　same　dot　at　one　and　the　same　time。　So　far　forth　then　as　it　takes　the　limit　as　two'　it　discriminates　two　separate　objects　with　what　in　a　sense　is　divided：　while　so　far　as　it　takes　it　as　one；　it　does　so　with　what　is　one　and　occupies　in　its　activity　a　single　moment　of　time。　　　About　the　principle　in　virtue　of　which　we　say　that　animals　are　percipient；　let　this　discussion　suffice。
  3
  There　are　two　distinctive　peculiarities　by　reference　to　which　we　characterize　the　soul　（1）　local　movement　and　（2）　thinking；　discriminating；　and　perceiving。　Thinking　both　speculative　and　practical　is　regarded　as　akin　to　a　form　of　perceiving；　for　in　the　one　as　well　as　the　other　the　soul　discriminates　and　is　cognizant　of　something　which　is。　Indeed　the　ancients　go　so　far　as　to　identify　thinking　and　perceiving；　e。g。　Empedocles　says　'For　'tis　in　respect　of　what　is　present　that　man's　wit　is　increased'；　and　again　'Whence　it　befalls　them　from　time　to　time　to　think　diverse　thoughts'；　and　Homer's　phrase　'For　suchlike　is　man's　mind'　means　the　same。　They　all　look　upon　thinking　as　a　bodily　process　like　perceiving；　and　hold　that　like　is　known　as　well　as　perceived　by　like；　as　I　explained　at　the　beginning　of　our　discussion。　Yet　they　ought　at　the　same　time　to　have　accounted　for　error　also；　for　it　is　more　intimately　connected　with　animal　existence　and　the　soul　continues　longer　in　the　state　of　error　than　in　that　of　truth。　They　cannot　escape　the　dilemma：　either　（1）　whatever　seems　is　true　（and　there　are　some　who　accept　this）　or　（2）　error　is　contact　with　the　unlike；　for　that　is　the　opposite　of　the　knowing　of　like　by　like。　　　But　it