The end and aim of spying in all its five varieties is knowledge of
the enemy;
I have ventured to differ in this place from those commentators—Tu
Yu and Chang Yü—who understand 主 as 人主, and make 五間之事 the
antecedent of 之 (the others ignoring the point altogether). It
is plausible enough that Sun Tzŭ should require the ruler to be
familiar with the methods of spying (though one would rather
expect 將 “general” in place of 主). But this involves taking 知之
here in quite a different way from the 知之 immediately following,
as also from those in the previous sentences. 之 there refers
vaguely to the enemy or the enemy’s condition, and in order to
retain the same meaning here, I make 主 a verb, governed by
五間之事. Cf. XI. § 19, where 主 is used in exactly the same
manner. The sole objection that I can see in the way of this
interpretation is the fact that the 死間, or fourth variety of spy,
does not add to our knowledge of the enemy, but only misinforms
the enemy about us. This would be, however, but a trivial
oversight on Sun Tzŭ’s part, inasmuch as the “doomed spy” is in
the strictest sense not to be reckoned as a spy at all. Capt.
Calthrop, it is hardly necessary to remark, slurs over the whole
difficulty.
and this knowledge can only be derived, in the first instance, from
the converted spy.
As explained in §§ 22–24. He not only brings information himself,
but makes it possible to use the other kinds of spy to advantage.
Hence it is essential that the converted spy be treated with the
utmost liberality.