虛實, literally “the hollow and the solid,” is the title of chap. VI. 碫 _tuan_ is the _T‘u Shu_ reading, 碬 _hsia_ that of the standard text. It appears from K‘ang Hsi that there has been much confusion between the two characters, and indeed, it is probable that one of them has really crept into the language as a mistake for the other. 5. 凡戰者以正合以奇勝 In all fighting, the direct method may be used for joining battle, but indirect methods will be needed in order to secure victory. Chang Yü says: 徐發奇兵或擣其旁或擊其後 “Steadily develop indirect tactics, either by pounding the enemy’s flanks or falling on his rear.” A brilliant example of “indirect tactics” which decided the fortunes of a campaign was Lord Roberts’ night march round the Peiwar Kotal in the second Afghan war.[169] 6. 故善出奇者無窮如天地不竭如江河終而復始日月是也死而復生四時是也 Indirect tactics, efficiently applied, are inexhaustible as Heaven and Earth, unending as the flow of rivers and streams; 奇 is the universally accepted emendation for 兵, the reading of the 北堂書鈔. like the sun and moon, they end but to begin anew; like the four seasons, they pass away but to return once more. Tu Yu and Chang Yü understand this of the permutations of 奇 and 正. But at present Sun Tzŭ is not speaking of 正 at all, unless, indeed, we suppose with 鄭友賢 Chêng Yu-hsien that a clause relating to it has fallen out of the text. Of course, as has already been pointed out, the two are so inextricably interwoven in all military operations, that they cannot really be considered apart. Here we simply have an expression, in figurative language, of the almost infinite resource of a great leader. 7. 聲不過五五聲之變不可勝聽也 There are not more than five musical notes, 宮商角微羽. yet the combinations of these five give rise to more melodies than can ever be heard. 8. 色不過五五色之變不可勝觀也 There are not more than five primary colours, 靑黃赤白黑 blue, yellow, red, white and black. yet in combination they produce more hues than can ever be seen. 9. 味不過五五味之變不可勝嘗也 There are not more than five cardinal tastes, 酸辛醎甘苦 sour, acrid, salt, sweet, bitter. yet combinations of them yield more flavours than can ever be tasted. 10. 戰埶不過奇正奇正之變不可勝窮也 In battle, there are not more than two methods of attack—the direct and the indirect; yet these two in combination give rise to an endless series of manœuvres. 11. 奇正相生如循環之無端孰能窮之 The direct and the indirect lead on to each other in turn. It is like moving in a circle—you never come to an end. Who can exhaust the possibilities of their combination? The _T‘u Shu_ adds 哉. The final 之 may refer either to the circle or, more probably, to the 奇正之變 understood. Capt. Calthrop is wrong with: “They are a mystery that none can penetrate.” 12. 激水之疾至於漂石者埶也 The onset of troops is like the rush of a torrent which will even roll stones along in its course. 13. 鷙鳥之疾至於毁折者節也 The quality of decision is like the well-timed swoop of a falcon which enables it to strike and destroy its victim.