have　been　discovered　for　the　cure　of　disease？　　Perhaps　in　this　way　we　may
  throw　some　light　on　the　question。　　It　appears　to　be　clear　that　whatever
  constitutes　wealth　must　be　useful；　and　that　wealth　is　one　class　of　useful
  things；　and　now　we　have　to　enquire；　What　is　the　use　of　those　useful　things
  which　constitute　wealth？　　For　all　things　probably　may　be　said　to　be　useful
  which　we　use　in　production；　just　as　all　things　which　have　life　are　animals；
  but　there　is　a　special　kind　of　animal　which　we　call　'man。'　　Now　if　any　one
  were　to　ask　us；　What　is　that　of　which；　if　we　were　rid；　we　should　not　want
  medicine　and　the　instruments　of　medicine；　we　might　reply　that　this　would　be
  the　case　if　disease　were　absent　from　our　bodies　and　either　never　came　to
  them　at　all　or　went　away　again　as　soon　as　it　appeared；　and　we　may　therefore
  conclude　that　medicine　is　the　science　which　is　useful　for　getting　rid　of
  disease。　　But　if　we　are　further　asked；　What　is　that　from　which；　if　we　were
  free；　we　should　have　no　need　of　wealth？　can　we　give　an　answer？　　If　we　have
  none；　suppose　that　we　restate　the　question　thus：If　a　man　could　live
  without　food　or　drink；　and　yet　suffer　neither　hunger　nor　thirst；　would　he
  want　either　money　or　anything　else　in　order　to　supply　his　needs？
  ERYXIAS：　　He　would　not。
  SOCRATES：　　And　does　not　this　apply　in　other　cases？　　If　we　did　not　want　for
  the　service　of　the　body　the　things　of　which　we　now　stand　in　need；　and　heat
  and　cold　and　the　other　bodily　sensations　were　unperceived　by　us；　there
  would　be　no　use　in　this　so…called　wealth；　if　no　one；　that　is；　had　any
  necessity　for　those　things　which　now　make　us　wish　for　wealth　in　order　that
  we　may　satisfy　the　desires　and　needs　of　the　body　in　respect　of　our　various
  wants。　　And　therefore　if　the　possession　of　wealth　is　useful　in　ministering
  to　our　bodily　wants；　and　bodily　wants　were　unknown　to　us；　we　should　not
  need　wealth；　and　possibly　there　would　be　no　such　thing　as　wealth。
  ERYXIAS：　　Clearly　not。
  SOCRATES：　　Then　our　conclusion　is；　as　would　appear；　that　wealth　is　what　is
  useful　to　this　end？
  Eryxias　once　more　gave　his　assent；　but　the　small　argument　considerably
  troubled　him。
  SOCRATES：　　And　what　is　your　opinion　about　another　question：Would　you　say
  that　the　same　thing　can　be　at　one　time　useful　and　at　another　useless　for
  the　production　of　the　same　result？
  ERYXIAS：　　I　cannot　say　more　than　that　if　we　require　the　same　thing　to
  produce　the　same　result；　then　it　seems　to　me　to　be　useful；　if　not；　not。
  SOCRATES：　　Then　if　without　the　aid　of　fire　we　could　make　a　brazen　statue；
  we　should　not　want　fire　for　that　purpose；　and　if　we　did　not　want　it；　it
  would　be　useless　to　us？　　And　the　argument　applies　equally　in　other　cases。
  ERYXIAS：　　Clearly。
  SOCRATES：　　And　therefore　conditions　which　are　not　required　for　the
  existence　of　a　thing　are　not　useful　for　the　production　of　it？
  ERYXIAS：　　Of　course　not。
  SOCRATES：　　And　if　without　gold　or　silver　or　anything　else　which　we　do　not
  use　directly　for　the　body　in　the　way　that　we　do　food　and　drink　and　bedding
  and　houses；if　without　these　we　could　satisfy　the　wants　of　the　body；　they
  would　be　of　no　use　to　us　for　that　purpose？
  ERYXIAS：　　They　would　not。
  SOCRATES：　　They　would　no　longer　be　regarded　as　wealth；　because　they　are
  useless；　whereas　that　would　be　wealth　which　enabled　us　to　obtain　what　was
  useful　to　us？
  ERYXIAS：　　O　Socrates；　you　will　never　be　able　to　persuade　me　that　gold　and
  silver　and　similar　things　are　not　wealth。　　But　I　am　very　strongly　of
  opinion　that　things　which　are　useless　to　us　are　not　wealth；　and　that　the
  money　which　is　useful　for　this　purpose　is　of　the　greatest　use；　not　that
  these　things　are　not　useful　towards　life；　if　by　them　we　can　procure　wealth。
  SOCRATES：　　And　how　would　you　answer　another　question？　　There　are　persons；
  are　there　not；　who　teach　music　and　grammar　and　other　arts　for　pay；　and　thus
  procure　those　things　of　which　they　stand　in　need？
  ERYXIAS：　　There　are。
  SOCRATES：　　And　these　men　by　the　arts　which　they　profess；　and　in　exchange
  for　them；　obtain　the　necessities　of　life　just　as　we　do　by　means　of　gold　and
  silver？
  ERYXIAS：　　True。
  SOCRATES：　　Then　if　they　procure　by　this　means　what　they　want　for　the
  purposes　of　life；　that　art　will　be　useful　towards　life？　　For　do　we　not　say
  that　silver　is　useful　because　it　enables　us　to　supply　our　bodily　needs？
  ERYXIAS：　　We　do。
  SOCRATES：　　Then　if　these　arts　are　reckoned　among　things　useful；　the　arts
  are　wealth　for　the　same　reason　as　gold　and　silver　are；　for；　clearly；　the
  possession　of　them　gives　wealth。　　Yet　a　little　while　ago　we　found　it
  difficult　to　accept　the　argument　which　proved　that　the　wisest　are　the
  wealthiest。　　But　now　there　seems　no　escape　from　this　conclusion。　　Suppose
  that　we　are　asked；　'Is　a　horse　useful　to　everybody？'　will　not　our　reply　be；
  'No；　but　only　to　those　who　know　how　to　use　a　horse？'
  ERYXIAS：　　Certainly。
  SOCRATES：　　And　so；　too；　physic　is　not　useful　to　every　one；　but　only　to　him
  who　knows　how　to　use　it？
  ERYXIAS：　　True。
  SOCRATES：　　And　the　same　is　the　case　with　everything　else？
  ERYXIAS：　　Yes。
  SOCRATES：　　Then　gold　and　silver　and　all　the　other　elements　which　are
  supposed　to　make　up　wealth　are　only　useful　to　the　person　who　knows　how　to
  use　them？
  ERYXIAS：　　Exactly。
  SOCRATES：　　And　were　we　not　saying　before　that　it　was　the　business　of　a　good
  man　and　a　gentleman　to　know　where　and　how　anything　should　be　used？
  ERYXIAS：　　Yes。
  SOCRATES：　　The　good　and　gentle；　therefore　will　alone　have　profit　from　these
  things；　supposing　at　least　that　they　know　how　to　use　them。　　But　if　so；　to
  them　only　will　they　seem　to　be　wealth。　　It　appears；　however；　that　where　a
  person　is　ignorant　of　riding；　and　has　horses　which　are　useless　to　him；　if
  some　one　teaches　him　that　art；　he　makes　him　also　richer；　for　what　was
  before　useless　has　now　become　useful　to　him；　and　in　giving　him　knowledge　he
  has　also　conferred　riches　upon　him。
  ERYXIAS：　　That　is　the　case。
  SOCRATES：　　Yet　I　dare　be　sworn　that　Critias　will　not　be　moved　a　whit　by　the
  argument。
  CRITIAS：　　No；　by　heaven；　I　should　be　a　madman　if　I　were。　　But　why　do　you
  not　finish　the　argument　which　proves　that　gold　and　silver　and　other　things
  which　seem　to　be　wealth　are　not　real　wealth？　　For　I　have　been　exceedingly
  delighted　to　hear　the　discourses　which　you　have　just　been　holding。
  SOCRATES：　　My　argument；　Critias　（I　said）；　appears　to　have　given　you　the
  same　kind　of　pleasure　which　you　might　have　derived　from　some　rhapsode's
  recitation　of　Homer；　for　you　do　not　believe　a　word　of　what　has　been　said。
  But　come　now；　give　me　an　answer　to　this　question。　　Are　not　certain　things
  useful　to　the　builder　when　he　is　building　a　house？
  CRITIAS：　　They　are。
  SOCRATES：　　And　would　you　say　that　those　things　are　useful　which　are
  employed　in　house　building；stones　and　bricks　and　beams　and　the　like；　and
  also　the　instruments　with　which　the　builder　built　the　house；　the　beams　and
  stones　which　they　provided；　and　again　the　instruments　by　which　these　were
  obtained？
  CRITIAS：　　It　seems　to　me　that　they　are　all　useful　for　building。
  SOCRATES：　　And　is　it　not　true　of　every　art；　that　not　only　the　materials　but
  the　instruments　by　which　we　procure　them　and　without　which　the　work　could
  not　go　on；　are　useful　for　that　art？
  CRITIAS：　　Certainly。
  SOCRATES：　　And　further；　the　instruments　by　which　the　instruments　are
  procured；　and　so　on；　going　back　from　stage　to　stage　ad　infinitum；are　not
  all　these；　in　your　opinion；　necessary　in　order　to　carry　out　the　work？
  CRITIAS：　　We　may　fairly　suppose　such　to　be　the　case。
  SOCRATES：　　And　if　a　man　has　food　and　drink　and　clothes　and　the　other　things
  which　are　useful　to　the　body；　would　he　need　gold　or　silver　or　any　other
  means　by　which　he　could　procure　that　which　he　now　has？
  CRITIAS：　　I　do　not　think　so。
  SOCRATES：　　Then　you　consider　that　a　man　never　wants　any　of　these　things　for
  the　use　of　the　body？
  CRITIAS：　　Certainly　not。
  SOCRATES：　　And　if　they　appear　useless　to　this　end；　ought　they　not　always　to
  appear　useless？　　For　we　have　already　laid　down　the　principle　that　things
  cannot　be　at　one　time　useful　and　at　another　time　not；　in　the　same　process。
  CRITIAS：　　But　in　that　respect　your　argument　and　mine　are　the　same。　　For　you
  maintain　if　they　are　useful　to　a　certain　end；　they　can　never　become
  useless；　whereas　I　say　that　in　order　to　accomplish　some　results　bad　things
  are　needed；　and　good　for　others。
  SOCRATES：　　But　can　a　bad　thing　be　used　to　carry　out　a　good　purpose？
  CRITIAS：　　I　should　say　not。
  SOCRATES：　　And　we　call　those　actions　good　which　a　man　does　for　the　sake　of
  virtue？
  CRITIAS：　　Yes。
  SOCRATES：　　But　can　a　man　learn　any　kind　of　knowledge　which　is　imparted　by
  word　of　mouth　if　he　is　wholly　deprived　of　the　sense　of　hearing？
  CRITIAS：　　Certainly　not；　I　think。
  SOCRATES：　　And　will　not　hearing　be　useful　for　virtue；　i