13. Use of Spies
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English translation
Original Chinese text
孙子曰:凡兴师十万,出征千里,百姓之费,公家之奉,日费千金,内外骚动,怠于道路,不得操事者,七十万家。相守数年,以争一日之胜,而爱爵禄百金,不知敌之情者,不仁之至也,非人之将也,非主之佐也,非胜之主也。故明君贤将,所以动而胜人,成功出于众者,先知也。先知者,不可取于鬼神,不可象于事,不可验于度,必取于人,知敌之情者也。
English translation
Mobilizing one hundred thousand troops for a thousand-li campaign carries immense cost: public expense, state supply, daily spending, and social disruption, plus paralysis in normal administration. The burden is equivalent to the labor of hundreds of thousands of households.
If rivals hold out for years over one day of victory and chase rank and pay while ignoring the enemy’s real situation, that is a profound failure of humane leadership. Such a person is not a competent commander, not a worthy assistant, and cannot be a true winner.
Hence, those who can move and prevail, and convert victory into broad success, are first and foremost those with prior knowledge. This prior knowledge cannot come from spirits or signs, nor from abstract measurement alone; it must be obtained from people who truly know the opponent.
The passage sets intelligence collection before mobilization. In modern terms, this is a governance rule for major operations: scale magnifies error, so accurate human intelligence is essential.
Original Chinese text
故用间有五:有乡间,有内间,有反间,有死间,有生间。五间俱起,莫知其道,是谓「神纪」,人君之宝也。乡间者,因其乡人而用之;内间者,因其官人而用之;反间者,因其敌间而用之;死间者,为诳事于外,令吾间知之,而传于敌间也;生间者,反报也。
English translation
There are five uses of intelligence agents: local, internal, turned, false, and returning agents. When all five are active and their pathways cannot be traced, that is called a divine arrangement, the ruler’s precious treasure.
Local agents are cultivated through people from the same local ties; internal agents through personnel in the adversary’s offices. Turned agents are obtained from enemy intelligence channels. False agents spread deceptive claims outside so our sources can hear and pass them inward. Returning agents provide counter-feedback.
The passage formalizes layered human intelligence. Diversity of channels provides cross-checking and lowers dependence on one uncertain source.
Original Chinese text
故三军之事,莫亲于间,赏莫厚于间,事莫密于间,非圣智不能用间,非仁义不能使间,非微妙不能得间之实。微哉!微哉!无所不用间也。间事未发而先闻者,间与所告者皆死。
English translation
In military work, nothing is closer than intelligence, and nothing deserves greater reward. The most secret matters are handled through intelligence work.
It demands uncommon judgment to use agents well, moral discipline to employ them rightly, and subtle skill to obtain what is real. So intelligence is deeply pervasive and must be broadly applied. If information is leaked before it is officially released, both the source and the recipient are to be punished.
This passage stresses governance of confidentiality. Intelligence provides advantage only when it is matched by strict accountability and disciplined handling.
Original Chinese text
凡军之所欲击,城之所欲攻,人之所欲杀,必先知其守将、左右、谒者、门者、舍人之姓名,令吾间必索知之。必索敌人之间来间我者,因而利之,导而舍之,故反间可得而用也;因是而知之,故乡间、内间可得而使也;因是而知之,故死间为诳事,可使告敌;因是而知之,故生间可使如期。五间之事,主必知之,知之必在于反间,故反间不可不厚也。
English translation
Before attacking a target, besieging a city, or striking an individual, the key is to know the names and roles of their command staff and gate officials first. This is an essential intelligence requirement.
First identify who among enemy-side agents may report to us, reward and steer them, and then let them disengage safely; this is how turned intelligence becomes useful. From that, local and internal agents can be deployed. From that, false agents can carry deceptive reports to the enemy. From that, returning agents can report on schedule. The ruler must understand all five functions, and the pivot is turned intelligence—so it must be valued and protected.
The text outlines an execution pipeline for intelligence operations. Practical advantage comes from controlling key people and channels of information, then coordinating specialized roles around verified data.
Original Chinese text
昔殷之兴也,伊挚在夏;周之兴也,吕牙在殷。故明君贤将,能以上智为间者,必成大功。此兵之要,三军之所恃而动也。
English translation
When Yin rose, Yi Zhi played his role within Xia; when Zhou rose, Lü Ya was effective within Yin. These examples show that a wise ruler and capable general who can elevate intelligence with superior judgment can achieve major success.
This is the essential point of warfare: the trust foundation for the whole army’s movement.
Historical cases are used to underline continuity of principle. Strategic power in any institution rests on information-led judgment and talent able to sustain it.