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I once studied the *Book of Changes* (*Yijing*) and heard from Confucius that: "Tracing the past follows the sequence (Shun), while knowing the future involves reverse deduction (Ni); therefore, the *Book of Changes* is based on reverse numbers (Ni Shu)." From this, I silently comprehended its principle and realized that the reason why the Dao of Heaven and Humanity remains endless and unceasing lies entirely in this reliance on "reverse numbers." Why is this? Generally speaking, since the Great Ultimate (Taiji) was initially divided and the Two Modes (Liangyi, i.e., Yin and Yang) were distinguished, through movement and stillness, the nature of Yin and Yang became manifest. The substance of Yin and Yang manifests as Qian (Heaven) and Kun (Earth), while their function manifests as Water and Fire. Qian and Kun establish the exchange of opposing positions, thus one is above and one is below; Water and Fire demonstrate the changes of flowing circulation, thus one governs descent and one governs ascent. In this manner, a cycle without end is achieved. Summarized, this constitutes the Dao of Heaven; dispersed, it becomes the Dao of Humanity. Thus, the profound meaning of the *Great Changes* is present in every minute detail. Let us not discuss other aspects, but simply clarify it through the principles of nature and reason: everything stems from the numbers of change (Bian Yi). The numbers of change are essentially the numbers of ascending and descending. The reason why change is infinite is that ascent serves as the master for descent; this is what is referred to as "reverse numbers" (Ni Shu). Without this "reverse," there would only be descent and no ascent, with qi flowing away and never returning. How could the Dao, like a circle, rely on anything then? Due to the alternating transformation of reverse and forward, Yang pairs with Yin, Heat pairs with Cold, Ascending pairs with Descending, Growth pairs with Decline, Advancing pairs with Retreating, Success pairs with Failure, Diligence pairs with Laziness, Labor pairs with Rest, Goodness pairs with Evil, and Life pairs with Death. All these instances involve one reverse and one forward, resulting in infinite variations. Those who follow the "reverse" align with Yang and attain life; those who follow the "forward" align with Yin and meet death. If you do not believe this, merely examine carefully the Round Diagram of Fuxi’s Hexagram Qi, and its meaning will be clearly visible. Observe that when Yang energy reaches its peak, starting from the Summer Solstice, a single Yin line begins to emerge. Passing through positions five, six, seven, and eight, and traversing the Xun, Kan, Gen, and Kun trigrams, the Dao of Heaven moves from West to Right. Consequently, Yang energy descends daily, and all things decline daily; these are all "forward numbers" (Shun Shu). Following the forward leads to the departure of qi, which is the path of aligning with Yin to meet death. Fortunately, when Yin peeling reaches its extreme, starting from the Winter Solstice, a single Yang line recovers. Passing through positions four, three, two, and one, and traversing the Zhen, Li, Dui, and Qian trigrams, the Dao of Heaven rotates from East to Left. Consequently, Yang energy ascends daily, and all things flourish daily; these are all "reverse numbers" (Ni Shu). Following the reverse leads to the arrival of qi, which is the path of aligning with Yang to attain life. This is the evidence of the Dao of Heaven, and it is indeed so.

If we speak of the Dao of Humanity, the Human Dao originates from the Heavenly Dao, and the Heart of Heaven is the Heart of Humanity. However, just as Heaven has haze that can obscure the sun and moon, humans have ignorance that can overshadow wisdom. Therefore, people often prefer to follow the "forward" because it is easy and comfortable; they often avoid the "reverse" because it is difficult and laborious. The perspective of the noble person (Junzi) is different. No one is more honorable than an emperor, who can enjoy ease and indulgence, yet Yao and Shun considered governance subtle and perilous, why must they constantly keep this in mind? No one is more intelligent than a sage, who should need no labor or fear, yet Confucius practiced caution and awe, why must he constantly hold this in his heart? There is no other reason; it is simply that they perform the functions of Heaven and preside over the ultimate standard of humanity. They fully understand that the forward path cannot be followed, for following it leads to drifting; the reverse path cannot be abandoned, for abandoning it leads to regression. From this, we see that if a scholar abandons the reverse, he suffers humiliation without extension; if a farmer abandons the reverse, he sows without harvest; if a craftsman abandons the reverse, he produces roughness without precision; if a merchant abandons the reverse, he disperses without gathering. Extending this further, regarding self-cultivation and family regulation, and governing the state and bringing peace to the world, advancing one step leads to daily success, while retreating one step leads to daily failure. Since there is both a source and a flow, how can one allow life to pass away endlessly without thinking of the good plan to act as a pillar against the current? This is the connection of the Human Dao, and it is thus significant.

However, whether speaking of Heaven or Humanity, it all concerns the Dao of Life. Among methods to preserve life, none is prior to medicine. If a doctor wishes to preserve life, how can he violate the Dao of Yang? How can he deviate from the reverse numbers? Yet medicine values flexibility and thorough understanding, allowing no rigidity. It does not mean completely ignoring Yin; following Yin is precisely to guard Yang. It does not mean completely avoiding the forward; using the forward is also to achieve the reverse. The mysterious gate of life and nature considers this the first priority. I only recall that some physicians of little renown remain ignorant of this, spreading heretical doctrines, which have been passed down to the present, causing harm to life and leaving deep repercussions. They cannot be described otherwise than as demons of Xuanyuan and Qibo (the mythical founders of Chinese Medicine). Alas! Alas! Who among us has a sincere heart? If such a person is found, one can discuss the Dao of returning to enlightenment with him. I hope you agree with my words.