Tunnels

Introduction

A "tunnel" attack digs from a distance to beneath the wall, props the shaft with timber, then burns the props so the wall collapses, or digs straight into the city. An attack you cannot see is the hardest to meet. Defense Against Tunnels opens with Qin Guli's question: the enemy comes through the earth, what then?

Mozi's answer is to listen first. Dig a well every five paces along the inside of the wall, close to its foot, down to just above the water table. Have the potters fire large jars (罂) of forty dou or more, cover the mouths with thin leather, and lower them into the wells. Post the sharpest-eared people lying on the jars. The sound of digging travels through the soil into the jar, and the leather amplifies it like a drumhead. Whichever well's jar sounds loudest, the tunnel lies that way. Then dig from inside to meet it: "cut a tunnel to receive them."

Then comes fighting underground. Potters make "moon-brights," half-round pottery pipes two and a half feet long, joined to carry smoke along the tunnel; a stove is built in the tunnel with four bellows attached to drive smoke into the enemy's shaft; when the two tunnels are about to meet, a ram is used to break through; those fighting below carry short weapons, shields and water. Every step has its trade: potters, smiths, listeners, bellows-workers.

墨门 / The Mohist Community has a fixed way of reading this chapter: listen, then act. A tunnel cannot be seen, so the first task is not to dig but to build something that can hear, turning the invisible into the judgeable. That is the real meaning of the second test: not "someone says so," but arranging for the facts to reach ears and eyes.

The three tests

The listening jar rests on the second test but pushes it to the edge: only the sharp-eared can hear. Mozi's solution is not to trust a few people's judgment but to let many wells confirm each other: the loudest one gives the direction. The lesson: "what people see and hear" does not require that everyone perceive it; it requires that perception be cross-checked. Discuss the Community's own versions this week. Finance, technology and law are often legible to a few. How do we design "many wells" so that others can verify?

For families

• 科技堂: stretch cling film over a bowl to make a "jar," put an ear to it and listen to light taps at the far end of the table; compare with and without the film.
• 科技堂: bury a phone playing soft music in a sand pile and have the children locate it by "listening" with a paper cup.
• "Listen, then act": when there is a disagreement this week, have each person first say what they heard the other say, then decide.

For chapters

• 20 min reading · 20 min 墨辩 · 10 min 三表 review · 10 min 职 reports.
• 墨辩 motion: "A fact only experts can verify still counts as 'what people see and hear.'" One side cites the jars and cross-checking wells; the other cites the text of Against Fate I.
• 三表 review: can an ordinary Mohist read the chapter's accounts and decision records? Design a "many wells" method, such as two non-finance members checking each quarter, and name them during 职 reports.