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Ancient sages said: "Observing the present requires taking the past as a mirror; without the past, there is no present." Both ancient and modern medicine should be referenced mutually. Examining medical texts from both eras cannot be fully enumerated here; I shall briefly mention the essential ones. For instance, *Shennong Bencao Jing* (Divine Farmer's Materia Medica), Xuanyuan's *Lingshu* (Spiritual Pivot) and *Suwen* (Basic Questions), Yue Ren's *Nanjing* (Classic of Difficult Issues), Changsha's *Yuhan Jing* (Jade Box Classic), as well as the works of the Four Great Masters—Liu, Li, Zhang, and Zhu—are all worthy of study.

Reading *Shennong Bencao Jing* allows one to understand that medicinal properties vary among Cold (Han), Heat (Re), Warm (Wen), Cool (Liang), and Neutral (Ping), and flavors differ among Sour (Suan), Bitter (Ku), Sweet (Gan), Acrid (Xin), and Salty (Xian), thereby clarifying what constitutes tonifying healthy Qi (Zheng Qi) versus expelling pathogenic factors (Xie Qi). Reading *Lingshu* and *Suwen* enables one to comprehend astronomy above and geography below, while also understanding the causes of disease in the Zang-Fu organs (Zang-Fu) and meridians (Jing-Luo). Reading *Nanjing* supplements the deficiencies of *Neijing* (Inner Canon) regarding pulse diagnosis (Mai Xiang), etiology, and the Eight Extraordinary Vessels (Qi Jing Ba Mai). Reading *Yuhan Jing* helps identify the origins of Shanghan (Cold Damage) and Zabing (Miscellaneous Diseases). These are medical classics by ancient sages and must be carefully studied and explored.

Regarding the Four Great Masters: Liu Wansu (courtesy name Shouzhen) of Hejian employed many bitter-cold methods; those treating Wenbing (Warm Diseases) and Rebing (Heat Diseases) should reference his approaches. Li Dongyuan (courtesy name Mingzhi) of Dongyuan utilized many lifting and tonifying methods; those treating Neishang Piwei (Internal Injury to Spleen and Stomach) should reference his methods. For cases of massive accumulation and aggregation (Da Ji Da Ju), one should refer to Zhang Congzheng (courtesy name Zihe) of Dairen’s purgative methods. For Yin deficiency with internal depletion (Yin Xu Nei Sun), one should examine Zhu Zhenheng (courtesy name Yanxiu) of Danxi’s clearing and tonifying methods. Not only do these four masters supplement the incompleteness of the ancient sages' works for reference, but later scholars' theories occasionally surpass even these four masters. Examples include Li Zhongzi (courtesy name Nian'e) from Yunjian, Yu Chang (courtesy name Jiayan) from Xichang, Wu Youxing (courtesy name Ke-you) from Yanling, Wang Kentang (courtesy name Yutai) from Jintan, Zhang Jingsui (courtesy name Jiabin) from Kuaiji, Zhang Lu from Changzhou, Xue Ji (courtesy name Lizhai) from Wujun, Ke Qin (courtesy name Yunbo) from Cixi, Shen Jin'ao (courtesy name Munan) from Xielii, and Zhang Zhicong (courtesy name Yin'an) from Qianjiang. All these gentlemen have authored works that should be adopted and consulted.

Examining contemporary medical texts also cannot be fully listed. For example, reading Ye Tianshi's (Ye Gui) *Linzheng Zhinan Yian* (Guide to Clinical Practice) reveals flexibility in clinical treatment and agility in prescription. Reading Zhang Nan's (courtesy name Xugu) *Yimen Banghe* (The Gavel of Medical Gate) exposes flaws and errors in renowned physicians' practices, awakening medical practitioners from their ignorance. Reading Wu Tang's (courtesy name Jutong) *Wenbing Tiaobian* (Systematic Differentiation of Warm Diseases) clarifies that Cold pathogens damage the Foot Meridians (Zu Jing), while Warm pathogens damage the Hand Meridians (Shou Jing). Reading Zhou Yangjun's (courtesy name Yu-zai) *Wenre Shuyi Quan Shu* (Complete Book on Warmth, Heat, Summer-heat, and Epidemic Diseases) elucidates that the sources of infection for warmth, heat, summer-heat, and epidemics are distinct. These are works by contemporary sages and should also be examined. Furthermore, Chen Nianzu (courtesy name Xiuyuan) from Changle, Cheng Guopeng (courtesy name Guanquan) from Xin'an, Wang Shixiong (courtesy name Mengying) from Yanguan, and Fei Boxiong from Wujin have transmitted their writings; occasional insights therein warrant reference and reflection.

I privately believe that while books have ancient and modern distinctions, so do people. Ancients possessed dense and robust constitution and Qi (Qi Ti), whereas modern people have gradually thinner constitutions. If one rigidly applies ancient prescriptions to treat modern diseases, would it not be overly burdensome? Therefore, physicians must not cling solely to ancient texts while ignoring modern ones, nor cling solely to modern texts while ignoring ancient ones. By referencing both ancient and modern knowledge, one naturally attains the Way of Harmony (Zhonghe) in medical theory.