Today, I'll talk about Using Spies,the thirteenth pieces of writing of The Art of War. Let's first look at its title which in broader sense involves the issue of military intelligence. involves the issue of military intelligence. so in this chapter he deals with the issue of spies, in other word, collecting military intelligence. At the beginning of this chapter, the author firstly paves the way and then proposes his idea. what way does he pave? "It took hundreds of thousands of soldiers several year and cost lots of money to win a battle in a day". So if a commander in chief doesn't rely on money and spies to collect military intelligence, he will be considered extremely foolish, In this sense,he firstly emphasizes the importance to collect intelligence Then, he puts forward his significant ideas. The first idea he puts forward is being a prophet. Here it doesn't refer to the prophet in religion. In classic Chinese, the word just means foreseeing the enemy. That is we need to get the upper hand by collecting enemy's military intelligence. If we know enemey's military intelligene, and the enemy don't know ours, we are initiative for we are in the shade, and the enemey are in the light. The enemy are passive for we know their military intelligence. The importance of foreseeing the enemy can be seen in our daily life. The wisdom in military confrontation in a sense, is just like playing chess. It is known to all chess players that when you play chess with a more skillful player. That is to say when we measure a player's skill, the norm is you can foresee how many moves of your rival. If you can foresee one or two moves, while your rival can foresee three or four moves, you'll feel hopeless when you play with your rival. So, foresing the enemy can help us get the upper hand in battle, which is the author's first viewpoint. Here comes the second one. How can we foresee the enemy? it is not sensible to do it through divination and analogy, which was usually conducted by the monarch and his ministers. However, Sun Zi disbelieved it, and insisted on the rational approach. Besides, he stresses it is impossible to foresee the enemy's military situation by analogy, and the right way is to use people. In other word, we must send professional spies to collect military intelligence. How do we send spies to collect military intelligence? Here Sun Zi classifies the ways of using spies into five categories. The first is the local spy. After occupying the enemy's territories, we can collect the military intelligence from the local people. The second is the inward spy, We can use large sum of money to bribe the enemy's officials to work for us, regardless of whether they are civil officials or military officials. The senior their positions are, the better. The third is the converted spy. We can use the enemy's spies we know, and then make use of large sum of money to bribe them in order to let them work for us. Today this kind of spies are called double agents, but the key is that we can make them work for us. The fourth is the doomed spy. We send the false intelligence to enemy on purpose. The intelligence is sent by our spies, Once the enemy believe this intelligence, they'll pay a heavy price in the battle, but when the enemy finally know the truth, our spies are doomed to die. That's why they're called doomed spies The fifth is the surviving spy, which is equal to the present scout. They are deep in the enemy's rear to collect the military intelligence. The above is the five categories of using spies. Sun Zi thinks "Wu Jian Ju Xia" "Mo Zhi Qi Dao" "Gui Shen Mo Bian" "Ru Ci Shi Ren Jian Zhi Bao" It means we should integratedly use these five kinds of spies so as to make the enemy confused, and thus make the full use of spies to achieve unpredictable results. That is the second aspect, five categories of using spies.