given　by　Tu　Mu：　　〃If　the　wind　is　in　the　east；　begin　burning　to
  the　east　of　the　enemy；　and　follow　up　the　attack　yourself　from
  that　side。　　If　you　start　the　fire　on　the　east　side；　　and　then
  attack　from　the　west；　you　will　suffer　in　the　same　way　as　your
  enemy。〃＇
  11。　　A　wind　that　rises　in　the　daytime　lasts　long；　　but　a
  night　breeze　soon　falls。
  ＇Cf。　　Lao　Tzu's　saying：　　〃A　violent　wind　does　not　last　the
  space　of　a　morning。〃　　（TAO　TE　CHING；　chap。　23。）　　　Mei　Yao…ch‘en
  and　Wang　Hsi　say：　　〃A　day　breeze　dies　down　at　nightfall；　　and　a
  night　breeze　at　daybreak。　　This　is　what　happens　as　a　general
  rule。〃　　　The　phenomenon　observed　may　be　correct　enough；　　but　how
  this　sense　is　to　be　obtained　is　not　apparent。＇
  12。　　In　every　army；　the　five　developments　connected　with
  fire　must　be　known；　the　movements　of　the　stars　calculated；　and　a
  watch　kept　for　the　proper　days。
  ＇Tu　Mu　says：　　〃We　must　make　calculations　as　to　the　paths　of
  the　stars；　　and　watch　for　the　days　on　which　wind　will　rise；
  before　making　our　attack　with　fire。〃　　Chang　Yu　seems　to　interpret
  the　text　differently：　　〃We　must　not　only　know　how　to　assail　our
  opponents　with　fire；　but　also　be　on　our　guard　against　similar
  attacks　from　them。〃＇
  13。　　Hence　those　who　use　fire　as　an　aid　to　the　attack　show
  intelligence；　those　who　use　water　as　an　aid　to　the　attack　gain　an
  accession　of　strength。
  14。　　By　means　of　water；　an　enemy　may　be　intercepted；　but　not
  robbed　of　all　his　belongings。
  ＇Ts‘ao　Kung's　note　is：　　〃We　can　merely　obstruct　the　enemy's
  road　or　divide　his　army；　but　not　sweep　away　all　his　accumulated
  stores。〃　　Water　can　do　useful　service；　but　it　lacks　the　terrible
  destructive　power　of　fire。　　This　is　the　reason；　　Chang　Yu
  concludes；　why　the　former　is　dismissed　in　a　couple　of　sentences；
  whereas　the　attack　by　fire　is　discussed　in　detail。　　Wu　Tzu　　（ch。
  4）　　speaks　thus　of　the　two　elements：　　〃If　an　army　is　encamped　on
  low…lying　marshy　ground；　from　which　the　water　cannot　run　off；　and
  where　the　rainfall　is　heavy；　it　may　be　submerged　by　a　flood。　　If
  an　army　is　encamped　in　wild　marsh　lands　thickly　overgrown　with
  weeds　and　brambles；　and　visited　by　frequent　gales；　　it　may　be
  exterminated　by　fire。〃＇
  15。　　Unhappy　is　the　fate　of　one　who　tries　to　win　his　battles
  and　succeed　in　his　attacks　without　cultivating　the　spirit　of
  enterprise；　　for　the　result　is　waste　of　time　and　　　general
  stagnation。
  ＇This　is　one　of　the　most　perplexing　passages　in　Sun　Tzu。
  Ts‘ao　Kung　says：　　　〃Rewards　for　good　service　should　not　be
  deferred　a　single　day。〃　　　And　Tu　Mu：　　　〃If　you　do　not　take
  opportunity　　　to　　　advance　and　reward　　　the　　　deserving；　　　your
  subordinates　will　not　carry　out　your　commands；　and　disaster　will
  ensue。〃　　　For　several　reasons；　however；　and　in　spite　of　the
  formidable　array　of　scholars　on　the　other　side；　　I　prefer　the
  interpretation　suggested　by　Mei　Yao…ch‘en　alone；　whose　words　I
  will　quote：　　〃Those　who　want　to　make　sure　of　succeeding　in　their
  battles　and　assaults　must　seize　the　favorable　moments　when　they
  come　and　not　shrink　on　occasion　from　heroic　measures：　　that　is　to
  say；　they　must　resort　to　such　means　of　attack　of　fire；　water　and
  the　like。　　What　they　must　not　do；　and　what　will　prove　fatal；　　is
  to　sit　still　and　simply　hold　to　the　advantages　they　have　got。〃＇
  16。　　Hence　the　saying：　　The　enlightened　ruler　lays　his　plans
  well　ahead；　the　good　general　cultivates　his　resources。
  ＇Tu　Mu　quotes　the　following　from　the　SAN　LUEH；　ch。　2：　　　〃The
  warlike　prince　controls　his　soldiers　by　his　authority；　kits　them
  together　by　good　faith；　and　by　rewards　makes　them　serviceable。
  If　faith　decays；　　there　will　be　disruption；　　if　rewards　are
  deficient；　commands　will　not　be　respected。〃＇
  17。　　Move　not　unless　you　see　an　advantage；　　use　not　your
  troops　unless　there　is　something　to　be　gained；　fight　not　unless
  the　position　is　critical。
  ＇Sun　Tzu　may　at　times　appear　to　be　over…cautious；　　but　he
  never　goes　so　far　in　that　direction　as　the　remarkable　passage　in
  the　TAO　TE　CHING；　ch。　69。　　〃I　dare　not　take　the　initiative；　　but
  prefer　to　act　on　the　defensive；　I　dare　not　advance　an　inch；　　but
  prefer　to　retreat　a　foot。〃＇
  18。　　No　ruler　should　put　troops　into　the　field　merely　to
  gratify　his　own　spleen；　no　general　should　fight　a　battle　simply
  out　of　pique。
  19。　　If　it　is　to　your　advantage；　make　a　forward　move；　　if
  not；　stay　where　you　are。
  ＇This　is　repeated　from　XI。　ss。　17。　　Here　I　feel　convinced
  that　it　is　an　interpolation；　for　it　is　evident　that　ss。　20　ought
  to　follow　immediately　on　ss。　18。＇
  20。　　Anger　may　in　time　change　to　gladness；　vexation　may　be
  succeeded　by　content。
  21。　　But　a　kingdom　that　has　once　been　destroyed　can　never
  come　again　into　being；
  ＇The　Wu　State　was　destined　to　be　a　melancholy　example　of
  this　saying。＇
  nor　can　the　dead　ever　be　brought　back　to　life。
  22。　　Hence　the　enlightened　ruler　is　heedful；　and　the　good
  general　full　of　caution。　　This　is　the　way　to　keep　a　country　at
  peace　and　an　army　intact。
  ＇1＇　　　〃Unless　you　enter　the　tiger's　lair；　you　cannot　get　hold　of
  the　tiger's　cubs。〃
  …
  XIII。　　THE　USE　OF　SPIES
  1。　　Sun　Tzu　said：　　Raising　a　host　of　a　hundred　thousand　men
  and　marching　them　great　distances　entails　heavy　loss　on　the
  people　and　a　drain　on　the　resources　of　the　State。　　The　daily
  expenditure　will　amount　to　a　thousand　ounces　of　silver。
  ＇Cf。　II。　ss。　ss。　1；　13；　14。＇
  There　will　be　commotion　at　home　and　abroad；　and　men　will　drop
  down　exhausted　on　the　highways。
  ＇Cf。　　TAO　TE　CHING；　　ch。　　30：　　　〃Where　troops　have　been
  quartered；　brambles　and　thorns　spring　up。　　Chang　Yu　has　the　note：
  〃We　may　be　reminded　of　the　saying：　　'On　serious　ground；　gather　in
  plunder。'　　　Why　then　should　carriage　and　transportation　cause
  exhaustion　on　the　highways？The　answer　is；　that　not　victuals
  alone；　　but　all　sorts　of　munitions　of　war　have　to　be　conveyed　to
  the　army。　　Besides；　the　injunction　to　'forage　on　the　enemy'　　only
  means　that　when　an　army　is　deeply　engaged　in　hostile　territory；
  scarcity　of　food　must　be　provided　against。　　Hence；　without　being
  solely　dependent　on　the　enemy　for　corn；　we　must　forage　in　order
  that　there　may　be　an　uninterrupted　flow　of　supplies。　　Then；
  again；　there　are　places　like　salt　deserts　where　provisions　being
  unobtainable；　supplies　from　home　cannot　be　dispensed　with。〃＇
  As　many　as　seven　hundred　thousand　families　will　be　impeded　in
  their　labor。
  ＇Mei　Yao…ch‘en　says：　　〃Men　will　be　lacking　at　the　plough…
  tail。〃　　The　allusion　is　to　the　system　of　dividing　land　into　nine
  parts；　each　consisting　of　about　15　acres；　the　plot　in　the　center
  being　cultivated　on　behalf　of　the　State　by　the　tenants　of　the
  other　eight。　　It　was　here　also；　so　Tu　Mu　tells　us；　　that　their
  cottages　were　built　and　a　well　sunk；　to　be　used　by　all　in　common。
  ＇See　II。　ss。　12；　note。＇　　In　time　of　war；　one　of　the　families　had
  to　serve　in　the　army；　while　the　other　seven　contributed　to　its
  support。　　Thus；　　by　a　levy　of　100；000　men　（reckoning　one　able…
  bodied　soldier　to　each　family）　the　husbandry　of　700；000　families
  would　be　affected。＇
  2。　　Hostile　armies　may　face　each　other　for　years；　　striving
  for　the　victory　which　is　decided　in　a　single　day。　　This　being　so；
  to　remain　in　ignorance　of　the　enemy's　condition　simply　because
  one　grudges　the　outlay　of　a　hundred　ounces　of　silver　in　honors
  and　emoluments；
  ＇〃For　spies〃　is　of　course　the　meaning；　though　it　would　spoil
  the　effect　of　this　curiously　elaborate　exordium　if　spies　were
  actually　mentioned　at　this　point。＇
  is　the　height　of　inhumanity。
  ＇Sun　Tzu's　agreement　is　certainly　ingenious。　　He　begins　by
  adverting　to　the　frightful　misery　and　vast　expenditure　of　blood
  and　treasure　which　war　always　brings　in　its　train。　　Now；　　unless
  you　are　kept　informed　of　the　enemy's　condition；　and　are　ready　to
  strike　at　the　right　moment；　a　war　may　drag　on　for　years。　　The
  only　way　to　get　this　information　is　to　employ　spies；　and　it　is
  impossible　to　obtain　trustworthy　spies　unless　they　are　properly
  paid　for　their　services。　　But　it　is　surely　false　economy　to
  grudge　a　comparatively　trifling　amount　for　this　purpose；　　when
  every　day　that　the　war　lasts　eats　up　an　incalculably　greater　sum。
  This　grievous　burden　falls　on　the　shoulders　of　the　poor；　　and
  hence　Sun　Tzu　concludes　that　to　neglect　the　use　of　spies　is
  nothing　less　than　a　crime　against　humanity。＇
  3。　　One　who　acts　thus　is　no　leader　of　men；　no　present　help
  to　his　sovereign；　no　master　of　victory。
  ＇This　idea；　that　the　true　object　of　war　is　peace；　　has　its
  root　in　the　national　temperament　of　the　Chinese。　　Even　so　far
  back　as　597　B。C。；　these　memorable　words　were　uttered　by　Prince
  Chuang　of　the　Ch‘u　State：　　〃The　＇Ch