useful　to　them　all。　Hence；　men　who　are　governed　by　reason　…　that　is；　who
  seek　what　is　useful　to　them　in　accordance　with　reason；　desire　for
  themselves　nothing；　which　they　do　not　also　desire　for　the　rest　of　mankind；
  and；　consequently；　are　just；　faithful；　and　honourable　in　their　conduct。
  Such　are　the　dictates　of　reason；　which　I　purposed　thus　briefly　to
  indicate；　before　beginning　to　prove　them　in　greater　detail。　I　have　taken
  this　course；　in　order；　if　possible；　to　gain　the　attention　of　those　who
  believe；　that　the　principle　that　every　man　is　bound　to　seek　what　is　useful
  for　himself　is　the　foundation　of　impiety；　rather　than　of　piety　and　virtue。
  Therefore；　after　briefly　showing　that　the　contrary　is　the　case；　I　go
  on　to　prove　it　by；　the　same　method；　as　that　whereby　I　have　hitherto
  proceeded。
  Prop。　XIX。　Every　man；　by　the　laws　of　his
  nature；　necessarily　desires　or　shrinks
  from　that　which　he　deems　to　be　good　or　bad。
  Proof。…　The　knowledge　of　good　and　evil　is　（IV：viii。）　the　emotion　of
  pleasure　or　pain；　in　so　far　as　we　are　conscious　thereof；　therefore；
  every　man　necessarily　desires　what　he　thinks　good；　and　shrinks　from
  what　he　thinks　bad。　Now　this　appetite　is　nothing　else　but　man's　nature
  or　essence　（Cf。　the　Definition　of　Appetite；　III。ix。note；　and　Def。　of
  the　Emotions；　i。）。　Therefore；　every　man；　solely　by　the　laws　of　his
  nature；　desires　the　one；　and　shrinks　from　the　other；　&c。　Q。E。D。
  Prop。　XX。　The　more　every　man　endeavours；
  and　is　able　to　seek　what　is　useful　to　him　…
  in　other　words；　to　preserve　his　own　being　…
  the　more　is　he　endowed　with　virtue；　on　the
  contrary；　in　proportion　as　a　man　neglects
  to　seek　what　is　useful　to　him；　that　is；　to
  preserve　his　own　being；　he　is　wanting　in　power。
  Proof。…　Virtue　is　human　power；　which　is　defined　solely　by　man's　essence
  （IV：Def。viii。）；　that　is；　which　is　defined　solely　by　the　endeavour　made　by
  man　to　persist　in　his　own　being。　Wherefore；　the　more　a　man　endeavours；
  and　is　able　to　preserve　his　own　being；　the　more　is　he　endowed　with　virtue；
  and；　consequently　（III：iv。&；vi。）；　in　so　far　as　a　man　neglects　to
  preserve　his　own　being；　he　is　wanting　in　power。　Q。E。D。
  Note。…　No　one；　therefore；　neglects　seeking　his　own　good；　or　preserving　his
  own　being；　unless　he　be　overcome　by　causes　external　and　foreign　to　his
  nature。　No　one；　I　say；　from　the　necessity　of　his　own　nature；　or　otherwise
  than　under　compulsion　from　external　causes；　shrinks　from　food；　or　kills
  himself：　which　latter　may　be　done　in　a　variety　of　ways。　A　man；　for
  instance；　kills　himself　under　the　compulsion　of　another　man；　who　twists
  round　his　right　hand；　wherewith　he　happened　to　have　taken　up　a　sword；　and
  forces　him　to　turn　the　blade　against　his　own　heart；　or；　again；　he　may　be
  compelled；　like　Seneca；　by　a　tyrant's　command；　to　open　his　own　veins　…
  that　is；　to　escape　a　greater　evil　by　incurring；　a　lesser；　or；　lastly；
  latent　external　causes　may　so　disorder　his　imagination；　and　so　affect　his
  body；　that　it　may　assume　a　nature　contrary　to　its　former　one；　and　whereof
  the　idea　cannot　exist　in　the　mind　（III：x。）　But　that　a　man；　from　the
  necessity　of　his　own　nature；　should　endeavour　to　become　non…existent；　is
  as　impossible　as　that　something　should　be　made　out　of　nothing；　as　everyone
  will　see　for　himself；　after　a　little　reflection。
  Prop。　XXI。　No　one　can　desire　to　be　blessed；
  to　act　rightly；　and　to　live　rightly；　without
  at　the　same　time　wishing　to　be；　act；　and　to
  live　…　in　other　words；　to　actually　exist。
  Proof。…　The　proof　of　this　proposition；　or　rather　the　proposition　itself；
  is　self…evident；　and　is　also　plain　from　the　definition　of　desire。　For　the
  desire　of　living；　acting；　&C。；　blessedly　or　rightly；　is　（Def。　of　the
  Emotions；　i。）　the　essence　of　man　…　that　is　（III：vii。）；　the　endeavour
  made　by　everyone　to　preserve　his　own　being。　Therefore；　no　one　can
  desire；　&c。　Q。E。D。
  Prop。　XXII。　No　virtue　can　be　conceived
  as　prior　to　this　endeavour　to　preserve
  one's　own　being。
  Proof。…　The　effort　for　self…preservation　is　the　essence　of　a　thing
  （III：vii。）；　therefore；　if　any　virtue　could　be　conceived　as　prior
  thereto；　the　essence　of　a　thing　would　have　to　be　conceived　as
  prior　to　itself；　which　is　obviously　absurd。　Therefore　no　virtue；　&c。
  Q。E。D。
  Corollary。…　The　effort　for　self…preservation　is　the　first　and　only
  foundation　of　virtue。　For　prior　to　this　principle　nothing　can　be
  conceived；　and　without　it　no　virtue　can　be　conceived。
  Prop。　XXIII。　Man；　in　so　far　as　he　is
  determined　to　a　particular　action
  because　he　has　inadequate　ideas；
  cannot　be　absolutely　said　to　act　in
  obedience　to　virtue；　he　can　only　be
  so　described；　in　so　far　as　he　is
  determined　for　the　action　because
  he　understands。
  Proof。…　In　so　far　as　a　man　is　determined　to　an　action　through　having
  inadequate　ideas；　he　is　passive　（III：i。）；　that　is　（III：Def。i。；　&iii。）；
  he　does　something；　which　cannot　be　perceived　solely　through　his　essence；
  that　is　（by　IV：Def。viii。）；　which　does　not　follow　from　his　virtue。　But；
  in　so　far　as　he　is　determined　for　an　action　because　he　understands；　he
  is　active；　that　is；　he　does　something；　which　is　perceived　through　his
  essence　alone；　or　which　adequately　follows　from　his　virtue。　Q。E。D。
  Prop。　XXIV。　To　act　absolutely　in　obedience
  to　virtue　is　in　us　the　same　thing　as　to　act；
  to　live；　or　to　preserve　one's　being　（these
  three　terms　are　identical　in　meaning）　in
  accordance　with　the　dictates　of　reason　on　the
  basis　of　seeking　what　is　useful　to　one's　self。
  Proof。…　To　act　absolutely　in　obedience　to　virtue　is　nothing　else　but
  to　act　according　to　the　laws　of　one's　own　nature。　But　we　only　act；　in
  so　far　as　we　understand　（III：iii。）　：　therefore　to　act　in　obedience　to
  virtue　is　in　us　nothing　else　but　to　act；　to　live；　or　to　preserve　one's
  being　in　obedience　to　reason；　and　that　on　the　basis　of　seeking　what　is
  useful　for　us　（IV：xxii。Coroll。）。　Q。E。D。
  Prop。　XXV。　No　one　wishes　to　preserve　his
  being　for　the　sake　of　anything　else。
  Proof。…　The　endeavour；　wherewith　everything　endeavours　to　persist　in　its
  being；　is　defined　solely　by　the　essence　of　the　thing　itself　（III：vii。）；
  from　this　alone；　and　not　from　the　essence　of　anything　else；　it　necessarily
  follows　（III：vi。）　that　everyone　endeavours　to　preserve　his　being。
  Moreover；　this　proposition　is　plain　from　IV：xxii。Coroll。；　for　if　a　man
  should　endeavour　to　preserve　his　being　for　the　sake　of　anything　else；　the
  last…named　thing　would　obviously　be　the　basis　of　virtue；　which；　by　the
  foregoing　corollary；　is　absurd。　Therefore　no　one；　&c。　Q。E。D。
  Prop。　XXVI。　Whatsoever　we　endeavour　in
  obedience　to　reason　is　nothing　further
  than　to　understand；　neither　does　the　mind；
  in　so　far　as　it　makes　use　of　reason；　judge
  anything　to　be　useful　to　it；　save　such
  things　as　are　conducive　to　understanding。
  Proof。…　The　effort　for　self…preservation　is　nothing　else　but　the　essence
  of　the　thing　in　question　（III：vii。）；　which；　in　so　far　as　it　exists　such
  as　it　is；　is　conceived　to　have　force　for　continuing　in　existence　（III：vi。）
  and　doing　such　things　as　necessarily　follow　from　its　given　nature　（see　the
  Def。　of　Appetite；　II：ix。Note）。　But　the　essence　of　reason　is　nought　else　but
  our　mind；　in　so　far　as　it　clearly　and　distinctly　understands　（see　the
  definition　in　II：xl。Note：ii。）　；　therefore　（III：xl。）　whatsoever　we　endeavour
  in　obedience　to　reason　is　nothing　else　but　to　understand。　Again；　since　this
  effort　of　the　mind　wherewith　the　mind　endeavours；　in　so　far　as　it　reasons；
  to　preserve　its　own　being　is　nothing　else　but　understanding；　this　effort
  at　understanding　is　（IV：xxii。Coroll。）　the　first　and　single　basis　of　virtue；
  nor　shall　we　endeavour　to　understand　things　for　the　sake　of　any　ulterior
  object　（IV：xxv。）；　on　the　other　hand；　the　mind；　in　so　far　as　it　reasons；
  will　not　be　able　to　conceive　any　good　for　itself；　save　such　things　as　are
  conducive　to　understanding。
  Prop。　XXVII。　We　know　nothing　to　be　certainly
  good　or　evil；　save　such　things　as　really
  conduce　to　understanding；　or　such　as　are
  able　to　hinder　us　from　understanding。
  Proof。…　The　mind；　in　so　far　as　it　reasons；　desires　nothing　beyond
  understanding；　and　judges　nothing　to　be　useful　to　itself；　save　such
  things　as　conduce　to　understanding　（by　the　foregoing　Prop。）。　But　the
  mind　（II：xli。&Note）　cannot　possess　certainty　concerning　anything；
  except　in　so　far　as　it　has　adequate　ideas；　or　（what　by　II：xl。Note；
  is　the　same　thing）　in　so　far　as　it　reasons。　Therefore　we　know