other　conditions　being　equal；　fainter　than　an
  emotion　towards　a　thing　past。
  Proof。…　In　so　far　as　we　conceive　a　thing　as　contingent；　we　are　not
  affected　by　the　image　of　any　other　thing；　which　asserts　the　existence
  of　the　said　thing　（IV：Def。iii。）；　but；　on　the　other　hand　（by　hypothesis）；
  we　conceive　certain　things　excluding　its　present　existence。　But；　in　so
  far　as　we　conceive　it　in　relation　to　time　past；　we　are　assumed　to
  conceive　something；　which　recalls　the　thing　to　memory；　or　excites　the
  image　thereof　（II：xviii。&Note）；　which　is　so　far　the　same　as　regarding
  it　as　present　（II：xvii。Coroll。）。　Therefore　（IV：ix。）　an　emotion　towards　a
  thing　contingent；　which　we　know　does　not　exist　in　the　present；　is　fainter；
  other　conditions　being　equal；　than　an　emotion　towards　a　thing　past。　Q。E。D。
  Prop。　XIV。　A　true　knowledge　of　good　and　evil
  cannot　check　any　emotion　by　virtue　of　being　true；
  but　only　in　so　far　as　it　is　considered　as　an　emotion。
  Proof。…　An　emotion　is　an　idea；　whereby　the　mind　affirms　of　its　body　a
  greater　or　less　force　of　existing　than　before　（by　the　general　Definition
  of　the　Emotions）；　therefore　it　has　no　positive　quality；　which　can　be
  destroyed　by　the　presence　of　what　is　true；　consequently　the　knowledge
  of　good　and　evil　cannot；　by　virtue　oi　being　true；　restrain　any　emotion。
  But；　in　so　far　as　such　knowledge　is　an　emotion　（IV：viii。）　if　it　have
  more　strength　for　restraining　emotion；　it　will　to　that　extent　be　able
  to　restrain　the　given　emotion。　Q。E。D。
  Prop。　XV。　Desire　arising　from　the
  knowledge　of　good　and　bad　can　be
  quenched　or　checked　by　many　of　the
  other　desires　arising　from　the
  emotions　whereby　we　are　assailed。
  Proof。…　From　the　true　knowledge　of　good　and　evil；　in　so　far　as　it　is　an
  emotion；　necessarily　arises　desire　（Def。　of　the　Emotions；　i。）；　the　strength
  of　which　is　proportioned　to　the　strength　of　the　emotion　wherefrom　it　arises
  （III：xxxvii。）。　But；　inasmuch　as　this　desire　arises　（by　hypothesis）　from　the
  fact　of　our　truly　understanding　anything；　it　follows　that　it　is　also
  present　with　us；　in　so　far　as　we　are　active　（III：i。）；　and　must　therefore
  be　understood　through　our　essence　only　（III：Def。ii。）；　consequently
  （III：vii。）　its　force　and　increase　can　be　defined　solely　by　human　power。
  Again；　the　desires　arising　from　the　emotions　whereby　we　are　assailed　are
  stronger；　in　proportion　as　the　said　emotions　are　more　vehement；　wherefore
  their　force　and　increase　must　be　defined　solely　by　the　power　of　external
  causes；　which；　when　compared　with　our　own　power；　indefinitely　surpass　it
  （IV：iii。）；　hence　the　desires　arising　from　like　emotions　may　be　more
  vehement；　than　the　desire　which　arises　from　a　true　knowledge　of　good　and
  evil；　and　may；　consequently；　control　or　quench　it。　Q。E。D。
  Prop。　XVI。　Desire　arising　from　the　knowledge
  of　good　and　evil；　in　so　far　as　such　knowledge
  regards　what　is　future；　may　be　more　easily
  controlled　or　quenched；　than　the　desire　for
  what　is　agreeable　at　the　present　moment。
  Proof。…　Emotion　towards　a　thing；　which　we　conceive　as　future；　is　fainter
  than　emotion　towards　a　thing　that　is　present　（IV：ix。Coroll。）。　But　desire；
  which　arises　from　the　true　knowledge　of　good　and　evil；　though　it　be
  concerned　with　things　which　are　good　at　the　moment；　can　be　quenched
  or　controlled　by　any　headstrong　desire　（by　the　last　Prop。；　the　proof
  whereof　is　of　universal　application）。　Wherefore　desire　arising　from
  such　knowledge；　when　concerned　with　the　future；　can　be　more　easily
  controlled　or　quenched；　&c。　Q。E。D。
  Prop。　XVII。　Desire　arising　from　the　true
  knowledge　of　good　and　evil；　in　so　far　as
  such　knowledge　is　concerned　with　what　is
  contingent；　can　be　controlled　far　more
  easily　still；　than　desire　for　things
  that　are　present。
  Proof。…　This　Prop。　is　proved　in　the　same　way　as　the　last　Prop。　from
  IV：xii。Coroll。
  Note。…　I　think　I　have　now　shown　the　reason；　why　men　are　moved　by　opinion
  more　readily　than　by　true　reason；　why　it　is　that　the　true　knowledge　of　good
  and　evil　stirs　up　conflicts　in　the　soul；　and　often　yields　to　every　kind　of
  passion。　This　state　of　things　gave　rise　to　the　exclamation　of　the　poet：
  （Ov。　Met。　vii。20；　〃Video　meliora　proboque；　Deteriora　sequor。〃）
  The　better　path　I　gaze　at　and　approve；
  The　worse　…　I　follow。〃
  Ecclesiastes　seems　to　have　had　the　same　thought　in　his　mind；　when　he　says；
  〃He　who　increaseth　knowledge　increaseth　sorrow。〃　I　have　not　written　the
  above　with　the　object　of　drawing　the　conclusion；　that　ignorance　is　more
  excellent　than　knowledge；　or　that　a　wise　man　is　on　a　par　with　a　fool　in
  controlling　his　emotions；　but　because　it　is　necessary　to　know　the　power
  and　the　infirmity　of　our　nature；　before　we　can　determine　what　reason　can
  do　in　restraining　the　emotions；　and　what　is　beyond　her　power。　I　have　said；
  that　in　the　present　part　I　shall　merely　treat　of　human　infirmity。　The
  power　of　reason　over　the　emotions　I　have　settled　to　treat　separately。
  Prop。　XVIII。　Desire　arising　from　pleasure　is；
  other　conditions　being　equal；　stronger　than
  desire　arising　from　pain。
  Proof。…　Desire　is　the　essence　of　a　man　（Def。　of　the　Emotions；　i。）；
  that　is；　the　endeavour　whereby　a　man　endeavours　to　persist　in　his　own
  being。　Wherefore　desire　arising　from　pleasure　is；　by　the　fact　of
  pleasure　being　felt；　increased　or　helped；　on　the　contrary；　desire
  arising　from　pain　is；　by　the　fact　of　pain　being　felt；　diminished　or
  hindered；　hence　the　force　of　desire　arising　from　pleasure　must　be
  defined　by　human　power　together　with　the　power　of　an　external　cause；
  whereas　desire　arising　from　pain　must　be　defined　by　human　power　only。
  Thus　the　former　is　the　stronger　of　the　two。　Q。E。D。
  Note。…　In　these　few　remarks　I　have　explained　the　causes　of　human　infirmity
  and　inconstancy；　and　shown　why　men　do　not　abide　by　the　precepts　of　reason。
  It　now　remains　for　me　to　show　what　course　is　marked　out　for　us　by　reason；
  which　of　the　emotions　are　in　harmony　with　the　rules　of　human　reason；　and
  which　of　them　are　contrary　thereto。
  But；　before　I　begin　to　prove　my　Propositions　in　detailed　geometrical
  fashion；　it　is　advisable　to　sketch　them　briefly　in　advance；　so　that
  everyone　may　more　readily　grasp　my　meaning。
  As　reason　makes　no　demands　contrary　to　nature；　it　demands；　that　every
  man　should　love　himself；　should　seek　that　which　is　useful　to　him　…　I　mean；
  that　which　is　really　useful　to　him；　should　desire　everything　which　really
  brings　man　to　greater　perfection；　and　should；　each　for　himself；　endeavour
  as　far　as　he　can　to　preserve　his　own　being。　This　is　as　necessarily　true；
  as　that　a　whole　is　greater　than　its　part。　（Cf。　III：iv。）
  Again；　as　virtue　is　nothing　else　but　action　in　accordance　with　the
  laws　of　one's　own　nature　（IV：Def。viii。）；　and　as　no　one　endeavours　to
  preserve　his　own　being；　except　in　accordance　with　the　laws　of　his　own
  nature；　it　follows；　first；　that　the　foundation　of　virtue　is　the　endeavour
  to　preserve　one's　own　being；　and　that　happiness　consists　in　man's　power
  of　preserving；　his　own　being；　secondly；　that　virtue　is　to　be　desired　for
  its　own　sake；　and　that　there　is　nothing　more　excellent　or　more　useful　to
  us；　for　the　sake　of　which　we　should　desire　it；　thirdly　and　lastly　that
  suicides　are　weak…minded；　and　are　overcome　by　external　causes　repugnant　to
  their　nature。　Further；　it　follows　from　Postulate　iv。　Part。II。；　that　we　can
  never　arrive　at　doing　without　all　external　things　for　the　preservation　of
  our　being　or　living；　so　as　to　have　no　relations　with　things
  which　are　outside　ourselves。　Again；　if　we　consider　our　mind；　we　see　that
  our　intellect　would　be　more　imperfect；　if　mind　were　alone；　and　could
  understand　nothing　besides　itself。　There　are；　then；　many　things　outside
  ourselves；　which　are　useful　to　us；　and　are；　therefore；　to　be　desired。
  Of　such　none　can　be　discerned　more　excellent；　than　those　which　are　in
  entire　agreement　with　our　nature。　For　if；　for　example；　two　individuals
  of　entirely　the　same　nature　are　united；　they　form　a　combination　twice
  as　powerful　as　either　of　them　singly。
  Therefore；　to　man　there　is　nothing　more　useful　than　man　…　nothing；
  I　repeat；　more　excellent　for　preserving　their　being　can　be　wished　for
  by　men；　than　that　all　should　so　in　all　points　agree；　that　the　minds　and
  bodies　of　all　should　form；　as　it　were；　one　single　mind　and　one　single
  body；　and　that　all　should；　with　one　consent；　as　far　as　they　are　able；
  endeavour　to　preserve　their　being；　and　all　with　one　consent　seek　what　is
  useful　to　them　all。　Hence；　men　who　are　governed　by　reason　…　that　is；　who
  seek　wha