Huangdi Neijing (Yellow Emperor’s Inner Canon), Nanjing (The Classic of Difficult Issues), and Shennong Bencao Jing (The Divine Farmer’s Materia Medica), compiled during the Qin and Han Dynasties, are important medical treatises that laid the theoretical foundation of traditional Chinese medicine (TCM). Together, they established the fundamental framework of the TCM system and remain its core classics to this day.

Huangdi Neijing (Yellow Emperor’s Inner Canon)

Huangdi Neijing (Yellow Emperor’s Inner Canon) is divided into two parts: Suwen (Plain Questions) and Lingshu (Spiritual Pivot). Most chapters are structured as dialogues between Huangdi (the Yellow Emperor) and Qibo, who was proficient in medical skills, through which many core theories of TCM are expounded. In the Yinyang Yingxiang Dalun (Great Treatise on the Correspondences of Yin and Yang) chapter of Suwen (Plain Questions), it states: “Yin and yang are the Dao of Heaven and Earth.” It regards yin-yang (yin and yang) as the fundamental law governing life activities. Physiologically, “when yin is balanced and yang is secured, the spirit is preserved”, and health is maintained; pathologically, “imbalance of yin and yang” gives rise to disease. In diagnosis and treatment, it emphasises: “Observe the complexion and palpate the pulse; first differentiate yin and yang.” This established the core framework of bianzheng lunzhi (pattern identification and treatment determination), guiding clinical practice in supplementation and draining, and in harmonising imbalance. Yinyang Yingxiang Dalun (Great Treatise on the Correspondences of Yin and Yang) also applies the five elements theory to elucidate the relationships of mutual generation and mutual restraint among the zang-fu (viscera and bowels). The liver, heart, spleen, lung, and kidney correspond respectively to the five elements. Physiologically, they generate and restrain one another; pathologically, they may overact or counteract upon one another. The five elements are applied to diagnosis, such as in the observation of facial complexion and pulse manifestations, and to treatment, as expressed in the principle: “In deficiency patterns, reinforce the mother (element); in excess patterns, reduce the child (element)”, thereby forming the zang-fu bianzheng (viscera and bowel pattern identification) system. The chapter Jingmai (The Meridians) of Lingshu (Spiritual Pivot) details the twelve meridians and their courses. Internally, they connect with the zang-fu; externally, they link with the limbs and joints, facilitating the circulation of qi (vital energy) and blood. Disorders in the meridian lead to pathological changes in the corresponding regions. For example, disease in the lung meridian of hand-Taiyin manifests as coughing and panting. Acupuncture treatment is based on meridian point selection, regulates qi and activates blood and lays the foundation for the clinical application of meridian theory. The chapter Wuzang Bielun (Treatise on the Five Zang) of Suwen (Plain Questions) defines the five zang organs as “storing the essence and qi without discharging them”, and distinguishes the six fu organs as “transmitting and transforming substances without storing them.” Each zang-fu performs specific functions; for example, the liver governs free coursing, and the stomach governs reception. Pathologically, they influence on another, such as liver fire invading the lung. Diagnosis and treatment often involve holistic regulation based on the correspondence between the five zang and the five elements, for example, zi shui han mu (nourishing Water to enrich Wood), which means nourishing the kidney to support the liver. This constitutes the core of zang-xiang (visceral manifestation) theory in traditional Chinese medicine. The chapter Zhi Zhen Yao Dalun (Great Treatise on the Essential and Ultimate) of Suwen (Plain Questions) identifies wind, cold, summer-heat, dampness, dryness, and fire as exogenous pathogenic factors. Wind is characterised by dispersion; cold by contraction; summer-heat is often accompanied by dampness; dampness is sticky and stagnant; dryness easily injures fluids; fire flares upward. These six exogenous pathogenic factors (liuyin) may cause disease singly or in combination and are related to individual constitution and environmental conditions, leading to externally contracted disorders or triggering internal dysfunctions and miscellaneous diseases.

Nanjing (The Classic of Difficult Issues)

According to some ancient medical authorities, Nanjing (The Classic of Difficult Issues) was compiled by the renowned Warring States physician Bian Que. It supplements aspects of meridian theory not fully elaborated in Huangdi Neijing (Yellow Emperor’s Inner Canon), stating: “The qi jing ba mai (eight extraordinary meridians) are not bound by the twelve regular meridians.” The eight extraordinary meridians interweave among the twelve meridians, strengthening their interconnections and regulating the circulation of qi and blood. The chapter Yi Nan (The First Difficult Issue) of Nanjing (The Classic of Difficult Issues) first proposed the method of “independent selection of the cunkou (inch-opening)” for pulse diagnosis, stating: “The cunkou is the great meeting of the vessels.” The establishment of pulse diagnosis at the Cunkou laid the foundation for standardised pulse-taking positions. The cun, guan, and chi positions reflect the qi of the five zang and six fu organs, and variations in floating and sinking indicate the severity of the disease. Bian Que places great emphasis on pulse-taking, and many chapters in Nanjing (The Classic of Difficult Issues) discuss pulse theory, consistent with his reputed expertise. The chapter San Shi Liu Nan (The Thirty-Sixth Difficult Issue) states: “The two kidneys are not both kidneys; the left is the kidney, the right is mingmen (gate of life).” Mingmen is described as “the residence of essence-spirit and the attachment of original qi.” Pathologically, abnormalities may manifest as failure to store essence in men or disorder of the uterus in women, highlighting the diverse functions of the kidney and its vital importance in the human body.

Shennong Bencao Jing (The Divine Farmer’s Materia Medica)

Shennong Bencao Jing (The Divine Farmer’s Materia Medica) is the earliest extant Chinese materia medica, systematically recording 365 medicinal substances. It pioneered the classification of medicinals into three grades: “the 120 superior medicinals are monarch and primarily nourish life to correspond with Heaven”; “the 120 middle-grade medicinals are ministerial and primarily nourish nature to correspond with Humanity”; “the 125 inferior-grade medicinals serve as assistants and guides primarily treating disease to correspond with Earth”. Superior medicinals may be taken long-term and are non-toxic, promoting longevity; middle-grade medicinals regulate deficiency and excess and require careful consideration; inferior medicinals attack pathogenic factors and should not be taken over prolonged periods. This classification established a hierarchical framework for the clinical application of Chinese medicines and laid the foundation for later toxicity categorisation. Shennong Bencao Jing (The Divine Farmer’s Materia Medica) also records the four qi (warm, hot, cold, and cool) and the five flavours (sour, bitter, sweet, pungent and salty) of medicinal substances. For example, Yiyiren (Job’s tears seed, Coicis Semen) is sweet in flavour and slightly cold in property. The four qi regulate yin-yang (yin and yang); the five flavours enter the five zang. Clinically, cold conditions are treated with heat, and heat conditions with cold; pungent disperses, sweet supplements, sour astringes, bitter drains, and salty softens hardness. The combined action of medicinal nature and flavour exerts therapeutic effects, harmonising qi (vital energy), blood, and yin-yang within the human body.