The sovereign must have full knowledge of the activities of the five sorts of agents. This knowledge must come from the double agents, and therefore it is mandatory that they be treated with the utmost liberality.

We cannot enter into alliances until we are acquainted with the designs of our neighbors. We are not fit to lead an army on the march unless we are familiar with the face of the country.

The business of a general is to kick away the ladder behind soldiers when they have climbed up a height.

He who is not sage and wise, humane and just, cannot use secret agent.s. And he who is not delicate and subtle cannot get the truth out of them.

The quality of decision is like the well-timed swoop of a falcon which enables it to strike and destroy its victim.

If the enemy leaves a door open, you must rush in.

Peace proposals unaccompanied by a sworn covenant indicate a plot.