（一）An Overview of Several Diagnostic Methods in Traditional Chinese Medicine (TCM) In the long history of TCM theory development, various diagnostic methods have gradually formed due to the deepening understanding of disease differentiation, such as the Eight Principles (Ba Gang) differentiation, etiology differentiation, meridian differentiation, Qi, Blood, and Body Fluids differentiation, San Jiao differentiation, Zang-Fu differentiation, Six Meridians differentiation, and Wei-Qi-Ying-Blood differentiation. 1. **Eight Principles Differentiation (Ba Gang Bian Zheng)** is a method for analyzing the common characteristics of diseases and serves as a framework for other differentiation methods. It plays a role in summarizing complex conditions and is applicable to various clinical specialties. In other words, all specialty differentiations are deepened based on the Eight Principles differentiation. Among them, the exterior-interior principle distinguishes the location of the disease; cold-heat and deficiency-excess differentiate the etiology and nature of the disease; Yin-Yang summarizes the disease syndromes. The Yin-Yang principles can also encompass the other six principles, with exterior, heat, and excess syndromes categorized as Yang, while interior, deficiency, and cold syndromes are categorized as Yin. Therefore, Yin-Yang is considered the overarching principle among the Eight Principles. 2. **Etiology Differentiation (Bing Yin Bian Zheng)** is a method for investigating the causes of diseases. In clinical practice, there are no symptoms without causes; any symptom arises from specific pathogenic factors acting on the body, resulting in pathological responses. In summary, the causes of disease can be divided into four aspects: Six Excesses (Liu Yin), Seven Emotions (Qi Qing), diet and lifestyle, and external injuries. 3. **Qi, Blood, and Body Fluids Differentiation (Qi Xue Jin Ye Bian Zheng)** is a method for identifying changes in Qi, Blood, or Body Fluids. The generation and movement of Qi, Blood, and Body Fluids rely on the functional activities of the Zang-Fu organs, which are the material basis for these activities. Therefore, in pathology, changes in Qi, Blood, and Body Fluids can affect the functions of the Zang-Fu organs, and dysfunction of these organs can lead to changes in Qi, Blood, and Body Fluids. Thus, Qi, Blood, and Body Fluids differentiation must be referenced alongside Zang-Fu differentiation. 4. **Zang-Fu Differentiation (Zang Fu Bian Zheng)** is a method for determining the location, nature, and the state of Zheng (correct Qi) and Xie (pathogenic Qi) in disease. It serves as the diagnostic foundation for various clinical specialties and is an important component of the differentiation system. Zang-Fu differentiation interrelates with Eight Principles differentiation, etiology differentiation, and Qi, Blood, and Body Fluids differentiation, requiring integration and connection in the differentiation process. Zang-Fu differentiation includes three parts: Zang disease differentiation, Fu disease differentiation, and combined Zang-Fu disease differentiation, with Zang disease differentiation being the primary focus. Due to the interconnection between the Zang and Fu organs, they can easily influence each other pathologically, leading to fewer discussions on Fu diseases. 5. **Meridian Differentiation (Jing Luo Bian Zheng)** is based on the theory of meridians to determine where the disease occurs in the meridians, Zang, or Fu, further clarifying the nature and development of the disease. This method differs from Zang-Fu differentiation and can complement it, being particularly important in clinical diagnosis, especially in acupuncture, massage, and Qigong. 6. **Wei-Qi-Ying-Blood Differentiation (Wei Qi Ying Xue Bian Zheng)** is a method used for diagnosing externally contracted warm diseases. Wei, Qi, Ying, and Blood represent four stages in the progression of warm diseases, indicating how the pathogenic factor gradually moves from the exterior to the interior, from superficial to deep, and from mild to severe. This means that Wei, Qi, Ying, and Blood represent four different types of syndromes: Wei syndrome, Qi syndrome, Ying syndrome, and Blood syndrome. When a warm pathogenic factor invades, it first affects the Wei level; if the Wei pathogen is not resolved, it enters the Qi level; if the Qi level is unresolved, the pathogenic factor further penetrates into the Ying level, where Ying is the Qi of Blood, and heat in the Ying level inevitably enters the Blood. The progression generally follows the order of Wei → Qi → Ying → Blood, although there can be reverse transmission not following this order. 7. **San Jiao Differentiation (San Jiao Bian Zheng)** is also a method for diagnosing warm diseases, originating from Qing dynasty scholar Wu Tang’s work on warm disease differentiation. San Jiao differentiation explains the pathological changes and symptom manifestations of the upper, middle, and lower Jiao, as well as the different stages of warm disease development. The initial stage of warm disease begins in the upper Jiao, involving symptoms of the Hand Taiyin Lung and Hand Jueyin Pericardium; if upper Jiao disease is untreated, it progresses to the middle Jiao, which includes symptoms of the Foot Yangming Stomach and Foot Taiyin Spleen; if the middle Jiao is untreated, it progresses to the lower Jiao, which includes symptoms of the Foot Shaoyin Kidney and Foot Jueyin Liver. Thus, San Jiao differentiation supplements the deficiencies of Wei-Qi-Ying-Blood differentiation and enriches and develops the content of Zang-Fu differentiation. 8. **Six Meridians Differentiation (Liu Jing Bian Zheng)** is a method for analyzing and summarizing the disease of cold damage based on the six meridians: Taiyang, Yangming, Shaoyang, Taiyin, Shaoyin, and Jueyin. According to the state of Zheng and Xie, the progression of the disease, and the manifestations at different stages, diseases are classified into Taiyang disease, Yangming disease, Shaoyang disease, Taiyin disease, Shaoyin disease, and Jueyin disease. The transmission of the six meridians generally starts from Taiyang, then moves to Shaoyang/Yangming; if the pathogenic factor further penetrates, it can enter the three Yin meridians, specifically the Taiyin meridian, and then progress to Shaoyin/Jueyin. However, there are cases where the pathogenic factor directly affects the three Yin meridians. In summary, the Eight Principles differentiation serves as the framework for differentiation; etiology differentiation focuses on the causes; Zang-Fu differentiation, Wei-Qi-Ying-Blood differentiation, San Jiao differentiation, and Six Meridians differentiation are further in-depth explorations based on the first two, forming the foundation for differentiation that can be widely applied to both externally contracted and internally injured diseases. (二) Methods and Key Points of Differentiation The process of differentiation is essentially a comprehensive analysis of various disease-related data collected through the four diagnostic methods, guided by the holistic perspective and based on the fundamental theories of TCM, to clarify the internal connections and gain an understanding of the essence of the disease, leading to a judgment of the syndrome. 1. **General Procedure of Differentiation**: Although each clinician may have different thinking methods during differentiation, rigid standardization is not feasible. However, we can identify some basic procedures from various flexible thinking forms. First, it is essential to comprehensively and accurately utilize the four diagnostic methods to collect relevant disease data as the basis for differentiation. Any omissions or errors in diagnosis can lead to incorrect differentiation. This requires us to be proficient and accurate in mastering the content and methods of the four diagnostic methods (observation, listening, inquiry, and pulse-taking). Second, based on Eight Principles differentiation, distinguish the Yin-Yang, exterior-interior, cold-heat, and deficiency-excess attributes of the disease. Third, apply etiology differentiation, Qi, Blood, and Body Fluids differentiation, and other foundational differentiation methods to preliminarily determine the etiology and pathogenesis of the disease. Next, based on the conclusions drawn from the above differentiation, if it is an externally contracted disease belonging to cold damage, then apply Six Meridians differentiation; if it is a warm disease, then apply Wei-Qi-Ying-Blood differentiation and San Jiao differentiation. If it is an internally injured miscellaneous disease, then use Zang-Fu differentiation and Meridian differentiation to determine its nature and location. After this series of differentiation results, it may be necessary to repeatedly apply the above differentiation methods to carefully discern to avoid errors. 2. **Key Points of Differentiation**: Focus on the main symptoms while considering the secondary ones. In differentiation, it is crucial to identify the main symptoms from the complex and variable clinical manifestations, as the main symptoms are often the key to differentiation. Grasping the pathological key allows for the exploration of other accompanying symptoms, laying the foundation for subsequent differentiation and treatment. However, focusing on the main symptoms does not mean neglecting the accompanying symptoms; without them, differentiation may be impossible or inaccurate. The main and accompanying symptoms are complementary, but emphasis should be placed on the main symptoms. Otherwise, failing to grasp the main symptoms and analyzing each symptom individually may lead to confusion in the face of complex syndromes, resulting in incorrect conclusions. For example, consider vomiting: one patient presents with headache, chills, fever, and vomiting; another patient suddenly experiences abdominal cramping, vomiting, and cold extremities, sometimes with roundworm vomiting; a third patient feels fatigued, weak, and has persistent vomiting after meals, with stools resembling sheep droppings. All three cases exhibit vomiting, but the first case is an externally contracted disease with vomiting as a secondary symptom; the second case is roundworm cramping, with vomiting and abdominal cramping being equally important (both are main symptoms); the third case is gastric reflux, with vomiting as the primary symptom; if vomiting were absent, the diagnosis of gastric reflux would not hold. 3. **Comprehensive Analysis Around Main Symptoms**: While grasping the main symptoms is crucial, it is also important not to overlook other symptoms and signs. Comprehensive collection of various disease manifestations is necessary to draw correct conclusions. Focus on the main symptoms as a clue to find accompanying symptoms, then conduct a comprehensive analysis to determine the etiology, nature, and location of the disease. 4. **Understanding Pathogenesis for Differentiation**: Due to the dynamic changes in the struggle between Zheng and Xie, diseases are in a state of constant evolution. The same disease may present different syndromes due to individual differences or the passage of time. Therefore, understanding the pathogenesis is significant for accurate differentiation. Once symptoms change, differentiation results should be adjusted accordingly. For instance, a patient with cold damage may present with symptoms in the Taiyang meridian today, but tomorrow they may have symptoms in the Shaoyang or Yangming meridian; or yesterday they may have had an exterior excess syndrome, but today, due to mismanagement or changes in pathogenesis, they may present with an exterior deficiency or other transformed syndrome. 5. **Special Individual Symptoms Can Guide Differentiation**: Generally, comprehensive analysis is the fundamental method of differentiation. However, certain unique individual symptoms may have guiding significance for differentiation and should not be overlooked. For example, patients with Yin deficiency and excess fire often exhibit “heat” symptoms in the head and face, while patients with floating Yang deficiency may also show “heat” phenomena in the head and face, despite their pathological essence being opposite. In this case, the coldness or warmth of the lower limbs and the characteristics of urination (short yellow or clear and long) become key points for differentiation. This does not contradict the detailed and comprehensive differentiation thought mentioned above, but rather complements it. Key symptoms are significant in judging the essence of the disease, and as symptoms, they reflect the objective phenomena of the entire disease essence, not existing in isolation from the whole. Therefore, differentiation should not be based solely on one or two “key” symptoms without considering the entire clinical picture. (三) Learning Methods for Differentiation Differentiation is based on the data from the four diagnostic methods, which are inseparable parts of the diagnostic process. Therefore, it is essential to first comprehensively and accurately master the content of the four diagnostic methods; otherwise, it is futile to expect correct differentiation. TCM differentiation is built upon the fundamental theoretical system of TCM, and the differentiation process is a specific application of these basic theories in clinical practice. For specific disease manifestations, understanding why analysis and synthesis are necessary and why only certain differentiation results can be obtained is determined by the basic theories. Pathological analysis must be conducted during differentiation, and basic theories must be applied for explanation. Therefore, it is crucial to fully grasp the content of TCM’s basic theories. When learning differentiation, it is important to establish connections between symptoms. The same symptom may appear in one syndrome and also in another; understanding the distinctions is essential for a deeper understanding of differentiation content. Writing is not easy, and I hope everyone can provide support and encouragement. In the following articles, I will discuss the Eight Principles, Zang-Fu differentiation, and specific operational methods.