back　as　597　B。C。；　these　memorable　words　were　uttered　by　Prince
  Chuang　of　the　Ch‘u　State：　　〃The　＇Chinese＇　character　for　'prowess'
  is　made　up　of　＇the　characters　for＇　'to　stay'　　and　　'a　spear'
  （cessation　of　hostilities）。　　Military　prowess　is　seen　in　the
  repression　　　of　　　cruelty；　　the　calling　in　of　　　weapons；　　　the
  preservation　of　the　appointment　of　Heaven；　the　firm　establishment
  of　merit；　　the　bestowal　of　happiness　on　the　people；　　putting
  harmony　between　the　princes；　the　diffusion　of　wealth。〃＇
  4。　　Thus；　　what　enables　the　wise　sovereign　and　the　good
  general　to　strike　and　conquer；　and　achieve　things　beyond　the
  reach　of　ordinary　men；　is　FOREKNOWLEDGE。
  ＇That　is；　knowledge　of　the　enemy's　dispositions；　and　what　he
  means　to　do。＇
  5。　　Now　this　foreknowledge　cannot　be　elicited　from　spirits；
  it　cannot　be　obtained　inductively　from　experience；
  ＇Tu　Mu's　note　is：　　〃＇knowledge　of　the　enemy＇　　cannot　be
  gained　by　reasoning　from　other　analogous　cases。〃＇
  nor　by　any　deductive　calculation。
  ＇Li　　　Ch‘uan　says：　　　〃Quantities　like　　　length；　　　breadth；
  distance　and　magnitude；　are　susceptible　of　exact　mathematical
  determination；　human　actions　cannot　be　so　calculated。〃＇
  6。　　Knowledge　of　the　enemy's　dispositions　can　only　be
  obtained　from　other　men。
  ＇Mei　Yao…ch‘en　has　rather　an　interesting　note：　　　〃Knowledge
  of　the　spirit…world　is　to　be　obtained　by　divination；　　information
  in　natural　science　may　be　sought　by　inductive　reasoning；　the　laws
  of　the　universe　can　be　verified　by　mathematical　calculation：　　but
  the　dispositions　of　an　enemy　are　ascertainable　through　spies　and
  spies　alone。〃＇
  7。　　Hence　the　use　of　spies；　of　whom　there　are　five　classes：
  （1）　　Local　spies；　　（2）　inward　spies；　（3）　　converted　spies；　　（4）
  doomed　spies；　（5）　surviving　spies。
  8。　　When　these　five　kinds　of　spy　are　all　at　work；　none　can
  discover　the　secret　system。　　This　is　called　〃divine　manipulation
  of　the　threads。〃　　It　is　the　sovereign's　most　precious　faculty。
  ＇Cromwell；　　one　of　the　greatest　and　most　practical　of　all
  cavalry　leaders；　　had　officers　styled　　'scout　masters；'　　whose
  business　it　was　to　collect　all　possible　information　regarding　the
  enemy；　through　scouts　and　spies；　etc。；　and　much　of　his　success　in
  war　was　traceable　to　the　previous　knowledge　of　the　enemy's　moves
  thus　gained。〃　＇1＇　＇
  9。　　Having　LOCAL　SPIES　means　employing　the　services　of　the
  inhabitants　of　a　district。
  ＇Tu　Mu　says：　　〃In　the　enemy's　country；　win　people　over　by
  kind　treatment；　and　use　them　as　spies。〃＇
  10。　　Having　INWARD　SPIES；　making　use　of　officials　of　the
  enemy。
  ＇Tu　Mu　enumerates　the　following　classes　as　likely　to　do　good
  service　in　this　respect：　　〃Worthy　men　who　have　been　degraded　from
  office；　　criminals　who　have　undergone　punishment；　also；　　favorite
  concubines　who　are　greedy　for　gold；　men　who　are　aggrieved　at
  being　in　subordinate　positions；　or　who　have　been　passed　over　in
  the　distribution　of　posts；　others　who　are　anxious　that　their　side
  should　be　defeated　in　order　that　they　may　have　a　chance　of
  displaying　their　ability　and　talents；　fickle　turncoats　who　always
  want　to　have　a　foot　in　each　boat。　　Officials　of　these　several
  kinds；〃　he　continues；　〃should　be　secretly　approached　and　bound　to
  one's　interests　by　means　of　rich　presents。　　In　this　way　you　will
  be　able　to　find　out　the　state　of　affairs　in　the　enemy's　country；
  ascertain　the　plans　that　are　being　formed　against　you；　　and
  moreover　disturb　the　harmony　and　create　a　breach　between　the
  sovereign　and　his　ministers。〃　　The　necessity　for　extreme　caution；
  however；　　in　dealing　with　　〃inward　spies；〃　　appears　from　　　an
  historical　incident　related　by　Ho　Shih：　　〃Lo　Shang；　Governor　of
  I…Chou；　sent　his　general　Wei　Po　to　attack　the　rebel　Li　Hsiung　of
  Shu　in　his　stronghold　at　P‘i。　　After　each　side　had　experienced　a
  number　of　victories　and　defeats；　Li　Hsiung　had　recourse　to　the
  services　of　a　certain　P‘o…t‘ai；　a　native　of　Wu…tu。　　He　began　to
  have　him　whipped　until　the　blood　came；　and　then　sent　him　off　to
  Lo　Shang；　whom　he　was　to　delude　by　offering　to　cooperate　with　him
  from　inside　the　city；　and　to　give　a　fire　signal　at　the　right
  moment　for　making　a　general　assault。　　Lo　Shang；　　confiding　in
  these　promises；　march　out　all　his　best　troops；　and　placed　Wei　Po
  and　others　at　their　head　with　orders　to　attack　at　P‘o…t‘ai's
  bidding。　　Meanwhile；　Li　Hsiung's　general；　Li　Hsiang；　had　prepared
  an　ambuscade　on　their　line　of　march；　and　P‘o…t‘ai；　having　reared
  long　scaling…ladders　against　the　city　walls；　　now　lighted　the
  beacon…fire。　　Wei　Po's　men　raced　up　on　seeing　the　signal　and
  began　climbing　the　ladders　as　fast　as　they　could；　　while　others
  were　drawn　up　by　ropes　lowered　from　above。　　More　than　a　hundred
  of　Lo　Shang's　soldiers　entered　the　city　in　this　way；　every　one　of
  whom　was　forthwith　beheaded。　　Li　Hsiung　then　charged　with　all　his
  forces；　　both　inside　and　outside　the　city；　and　routed　the　enemy
  completely。〃　　＇This　happened　in　303　A。D。　　I　do　not　know　where　Ho
  Shih　got　the　story　from。　　It　is　not　given　in　the　biography　of　Li
  Hsiung　or　that　of　his　father　Li　T‘e；　CHIN　SHU；　ch。　120；　121。＇
  11。　　Having　CONVERTED　SPIES；　getting　hold　of　the　enemy's
  spies　and　using　them　for　our　own　purposes。
  ＇By　means　of　heavy　bribes　and　liberal　promises　detaching
  them　from　the　enemy's　service；　and　inducing　them　to　carry　back
  false　information　as　well　as　to　spy　in　turn　on　their　own
  countrymen。　　On　the　other　hand；　Hsiao　Shih…hsien　says　that　we
  pretend　not　to　have　detected　him；　but　contrive　to　let　him　carry
  away　a　false　impression　of　what　is　going　on。　　Several　of　the
  commentators　accept　this　as　an　alternative　definition；　but　that
  it　is　not　what　Sun　Tzu　meant　is　conclusively　proved　by　his
  subsequent　remarks　about　treating　the　converted　spy　generously
  （ss。　21　sqq。）。　　Ho　Shih　notes　three　occasions　on　which　converted
  spies　were　used　with　conspicuous　success：　　（1）　by　T‘ien　Tan　in
  his　defense　of　Chi…mo　（see　supra；　p。　90）；　（2）　by　Chao　She　on　his
  march　to　O…yu　（see　p。　57）；　and　by　the　wily　Fan　Chu　in　260　B。C。；
  when　Lien　P‘o　was　conducting　a　defensive　campaign　against　Ch‘in。
  The　King　of　Chao　strongly　disapproved　of　Lien　P‘o's　cautious　and
  dilatory　methods；　　which　had　been　unable　to　avert　a　series　of
  minor　disasters；　and　therefore　lent　a　ready　ear　to　the　reports　of
  his　spies；　　who　had　secretly　gone　over　to　the　enemy　and　were
  already　in　Fan　Chu's　pay。　　They　said：　　〃The　only　thing　which
  causes　Ch‘in　anxiety　is　lest　Chao　Kua　should　be　made　general。
  Lien　P‘o　they　consider　an　easy　opponent；　who　is　sure　to　be
  vanquished　in　the　long　run。〃　　Now　this　Chao　Kua　was　a　sun　of　the
  famous　Chao　She。　　From　his　boyhood；　he　had　been　wholly　engrossed
  in　the　study　of　war　and　military　matters；　until　at　last　he　came
  to　believe　that　there　was　no　commander　in　the　whole　Empire　who
  could　stand　against　him。　　His　father　was　much　disquieted　by　this
  overweening　conceit；　　and　the　flippancy　with　which　he　spoke　of
  such　a　serious　thing　as　war；　and　solemnly　declared　that　if　ever
  Kua　was　appointed　general；　he　would　bring　ruin　on　the　armies　of
  Chao。　　This　was　the　man　who；　in　spite　of　earnest　protests　from
  his　own　mother　and　the　veteran　statesman　Lin　Hsiang…ju；　was　now
  sent　to　succeed　Lien　P‘o。　　Needless　to　say；　he　proved　no　match
  for　the　redoubtable　Po　Ch‘i　and　the　great　military　power　of
  Ch‘in。　　He　fell　into　a　trap　by　which　his　army　was　divided　into
  two　and　his　communications　cut；　and　after　a　desperate　resistance
  lasting　46　days；　during　which　the　famished　soldiers　devoured　one
  another；　he　was　himself　killed　by　an　arrow；　and　his　whole　force；
  amounting；　　it　is　said；　to　400；000　men；　ruthlessly　put　to　the
  sword。＇
  12。　　Having　DOOMED　SPIES；　doing　certain　things　openly　for
  purposes　of　deception；　and　allowing　our　spies　to　know　of　them　and
  report　them　to　the　enemy。
  ＇Tu　Yu　gives　the　best　exposition　of　the　meaning：　　　〃We
  ostentatiously　do　thing　calculated　to　deceive　our　own　spies；　　who
  must　be　led　to　believe　that　they　have　been　unwittingly　disclosed。
  Then；　　when　these　spies　are　captured　in　the　enemy's　lines；　　they
  will　make　an　entirely　false　report；　and　the　enemy　will　take
  measures　accordingly；　　only　to　find　that　we　do　something　quite
  different。　　The　spies　will　thereupon　be　put　to　death。〃　　　As　an
  example　of　doomed　spies；　Ho　Shih　mentions　the　prisoners　released
  by　Pan　Ch‘ao　in　his　campaign　against　Yarkand。　　（See　p。　132。）　　　He
  also　refers　to　T‘ang　Chien；　who　in　630　A。D。　was　sent　by　T‘ai
  Tsung　to　lull　the　Turkish　Kahn　Chieh…li　into　fancied　security；
  until　Li　Ching　was　able　to　deliver　a　crushing　blow　against　him。
  Chang　Yu　says　that　the　Turks　revenged　themselves　by　killing　T‘ang
  Chien；　but　this　is　a　mistake；　for　we　read　in　both　the　old　and　the
  New　　　T‘ang　History　　（ch。　　58；　　fol。　　2　and　ch。　　89；　　fol。