Comprehensive Guide to the Eight Principles of Diagnosis in Traditional Chinese Medicine

Diagnosis, or “bianzheng” (辨证), refers to the analysis and identification of disease syndromes, which is a primary process and method for understanding and diagnosing diseases. “Bian” (辨) means to discern and analyze, while “zheng” (证) refers to syndromes, which are comprehensive manifestations of the body’s disordered relationships under the influence of pathogenic factors and conditions, as well as between the body and the environment, organs, meridians, qi, blood, and body fluids. Therefore, clarifying a specific syndrome summarizes the pathological conditions of the disease’s development stage, including the causes, locations, strengths of the pathogenic and righteous forces, and the imbalances of yin and yang.
The process of diagnosis is based on theories of organs, meridians, qi, blood, body fluids, and pathogenic factors, and involves the comprehensive collection, induction, analysis, reasoning, judgment, and clarification of the internal relationships among symptoms and signs gathered through the four diagnostic methods: observation, listening, inquiry, and palpation. This allows for an understanding of the disease and the formulation of an accurate diagnosis.
Diagnosis and treatment are two crucial interrelated aspects of TCM theory, methods, formulas, and medicines in clinical practice. Diagnosis is the understanding of the disease, while treatment involves taking corresponding therapeutic measures and methods based on the diagnosed syndrome. Diagnosis is the premise and basis for treatment, while treatment is the objective of diagnosis and an objective standard for verifying the correctness of the diagnosis.
“Symptom” refers to individual symptoms, which are recognized similarly in both Chinese and Western medicine, such as headache, fever, cough, palpitations, nausea, etc.
“Disease” refers to the name of the disease. Among the disease names in TCM, only a few correspond to Western medical terms, such as measles, diphtheria, tetanus, asthma, dysentery, and heat stroke, while most terms differ. Due to the differences in theoretical systems, the understanding of diseases varies between TCM and Western medicine. Western medicine’s understanding of diseases is based on human anatomy and pathophysiology, with clinical diagnosis relying on the patient’s subjective symptoms, physical examination, and laboratory tests. TCM, on the other hand, views diseases as results of imbalances in yin and yang, with clinical diagnosis primarily based on the patient’s symptoms and signs (such as tongue and pulse), without necessarily determining the disease name but rather clarifying the “syndrome”.
“Zheng” (证) is an abbreviation for evidence or syndrome, which is not merely a symptom or subjective feeling but a group of syndromes. It is TCM’s diagnostic concept of disease. “Zheng” encompasses a set of specific clinical manifestations (symptoms, signs, etc.) and includes a comprehensive concept of the cause, location, nature of the disease, and the comparative strength of the righteous and pathogenic forces. “Zheng” is derived from analyzing symptoms and signs and is summarized into a concept that better explains the essence of the disease.
TCM diagnosis has developed through long-term clinical practice, employing various methods, primarily including the Eight Principles of Diagnosis, etiology diagnosis, diagnosis based on qi, blood, essence, and body fluids, organ diagnosis, and diagnosis based on defensive qi, nutritive qi, and blood, as well as the diagnosis of the three burners and the six channels. Among these, the Eight Principles of Diagnosis is the overarching principle of various diagnostic methods.
The Eight Principles of Diagnosis is a comprehensive analysis based on materials obtained from the four diagnostic methods, aimed at exploring the nature of the disease, the location of the pathological changes, the severity of the disease, the strength of the body’s response, and the comparative strength of the righteous and pathogenic forces, categorizing them into eight types of syndromes: yin, yang, exterior, interior, cold, heat, deficiency, and excess. This is a fundamental method of TCM diagnosis, encompassing the general principles of various diagnostic methods and serving to simplify complex disease presentations, revealing the contradictions in the disease process.
Although the manifestations of diseases are extremely complex, they can generally be categorized into the Eight Principles. The overall categories of diseases include yin syndromes and yang syndromes; the depth of the disease can be classified as exterior or interior; imbalances in yin and yang, with yang excess or yin deficiency leading to heat syndromes, and yang deficiency or yin excess leading to cold syndromes; the strength of the pathogenic and righteous forces, with strong pathogenic qi termed excess syndrome and weak righteous qi termed deficiency syndrome. Therefore, the Eight Principles of Diagnosis analyzes the myriad changes in diseases according to the simple dichotomies of exterior and interior, cold and heat, deficiency and excess, yin and yang, fully exposing the contradictions in the disease process. This embodies the fundamental spirit of the Eight Principles.
1. Exterior and Interior
Exterior and interior refer to the depth of the disease and the severity of the condition. Generally speaking, the skin, hair, and superficial muscles belong to the exterior; the organs, blood vessels, bone marrow, and internal meridians belong to the interior. Exterior syndromes indicate that the disease is superficial, with a mild condition; interior syndromes indicate that the disease is deep within the organs, with a severe condition.
(1) Exterior Syndrome
Exterior syndrome refers to syndromes located superficially in the skin. Generally, this occurs when external pathogenic factors invade the body through the skin and nose, leading to a series of symptoms where the righteous qi (defensive qi) resists the pathogenic factors, often seen in the initial stages of externally contracted diseases. Exterior syndromes are characterized by sudden onset, short duration, superficial location, and mild severity. They are commonly seen in the early stages of external heat diseases, such as upper respiratory infections, acute infectious diseases, and other initial stages of infectious diseases.
Main symptoms: fever and chills (or aversion to wind), headache, thin white tongue coating, and floating pulse are the basic symptoms, often accompanied by soreness in the limbs and joints, nasal congestion, cough, and other symptoms.
Due to the differences in the nature of external pathogenic factors (cold or heat), and the varying strengths of the body’s ability to resist these factors, exterior syndromes can be further divided into exterior cold, exterior heat, exterior deficiency, and exterior excess syndromes.
1. Exterior Cold Syndrome
Main symptoms: significant aversion to cold, mild fever, pronounced pain in the head and body, no sweating, clear nasal discharge, and no thirst. The tongue is pale red, with a thin white and moist coating, and the pulse is floating and tight.
Pathogenesis: Cold pathogenic factors are constrained in the skin or muscle layer, leading to a struggle between the righteous and pathogenic forces, hence the aversion to cold and mild fever. The invasion of pathogenic qi into the superficial meridians causes stagnation in the flow of defensive qi and blood, resulting in soreness in the head, body, and limbs. The pulse is floating due to the struggle between the righteous and pathogenic forces.
Treatment principle: Release the exterior with warm acrid herbs.
Common formula: Ma Huang Tang (Ephedra Decoction)
2. Exterior Heat Syndrome
Main symptoms: significant fever, mild aversion to cold, headache, sore throat, sweating, and thick yellow nasal discharge, with thirst. The tongue is slightly red, with a thin white coating that is not moist, and the pulse is floating and rapid.
Pathogenesis: The struggle between the righteous and pathogenic forces at the exterior leads to fever and mild aversion to cold. Heat pathogenic factors invade the defensive layer, causing sweating. Heat damages body fluids, leading to thirst. Heat in the exterior results in a floating and rapid pulse.
Treatment principle: Release the exterior with cool acrid herbs.
Common formula: Yin Qiao San (Honeysuckle and Forsythia Powder)
3. Exterior Deficiency Syndrome
Main symptoms: exterior syndrome with aversion to wind, sweating. The tongue is pale, with a thin white coating, and the pulse is floating and weak.
Pathogenesis: The patient has a weak constitution, and the defensive yang is not firm, leading to aversion to wind and sweating. The pulse is floating and weak.
Treatment principle: Harmonize the nutritive and defensive qi, and release the exterior.
Common formula: Gui Zhi Tang (Cinnamon Twig Decoction)
4. Exterior Excess Syndrome
Main symptoms: fever, aversion to cold, body aches, and no sweating. The tongue is pale red, with a thin white coating, and the pulse is floating and forceful.
Pathogenesis: The pathogenic factor is strong, and the righteous qi is not weakened. The pathogenic factor constrains the skin, and the righteous qi resists the pathogenic factor, leading to fever and aversion to cold without sweating. The pulse is floating and forceful.
Treatment principle: Release the exterior with warm acrid herbs.
Common formula: Ma Huang Tang (Ephedra Decoction)
Differentiating between exterior cold and exterior heat syndromes is based on the severity of aversion to cold and fever, as well as the tongue and pulse characteristics. Exterior cold syndrome presents with significant aversion to cold and mild fever, while exterior heat syndrome presents with significant fever and mild aversion to cold. The tongue coating in exterior cold syndrome is thin, white, and moist, with a tight floating pulse, while in exterior heat syndrome, the tongue coating is thin, white, and not moist, with a floating and rapid pulse. Additionally, wind-cold can transform into heat, and exterior cold syndrome can evolve into interior heat syndrome.
Differentiating between exterior deficiency and exterior excess syndromes involves considering the patient’s constitution, with sweating indicating deficiency and no sweating indicating excess. Exterior excess syndrome is often seen in younger, robust individuals, while exterior deficiency syndrome is more common in older, weaker, or chronically ill patients.
(2) Interior Syndrome
Interior syndrome, in contrast to exterior syndrome, refers to syndromes located deeper within the body (organs, qi, blood, bone marrow, etc.). The causes of interior syndromes can generally be classified into three categories: 1) the progression of an exterior syndrome, where the exterior pathogenic factor has not been resolved and has penetrated into the interior, affecting the organs; 2) direct invasion of external pathogenic factors into the internal organs, such as abdominal cold or excessive consumption of cold foods leading to interior cold syndrome; 3) internal injuries from emotional disturbances, overexertion, or dietary factors that directly impair organ function, leading to symptoms such as dizziness and pain in the hypochondrium from liver disease, palpitations and shortness of breath from heart disease, cough and wheezing from lung disease, abdominal distension and diarrhea from spleen disease, and low back pain and urinary retention from kidney disease. Therefore, the clinical manifestations of interior syndromes are complex, and all symptoms that are not exterior syndromes belong to interior syndromes. In cases of externally contracted diseases, interior syndromes should be differentiated based on etiology and the condition of the defensive qi, nutritive qi, and blood, while in cases of internal injuries, organ differentiation should be the primary focus. Interior syndromes need to be differentiated into interior cold, interior heat, interior deficiency, and interior excess (discussed in the context of cold-heat and deficiency-excess differentiation).
Differentiating between exterior and interior syndromes is primarily based on the patient’s history, the nature of the symptoms, and changes in the tongue coating and pulse. Generally, new or acute diseases with a short duration are more likely to be exterior syndromes, while chronic or long-standing diseases are often interior syndromes. Fever with aversion to cold indicates an exterior syndrome, while fever without aversion to cold or only cold without fever indicates an interior syndrome. The tongue coating in exterior syndromes often shows no changes or only slight redness at the edges, while interior syndromes often present with abnormal tongue coatings. A floating pulse indicates an exterior syndrome, while a deep pulse indicates an interior syndrome.
(3) Half-Exterior Half-Interior Syndrome
This refers to syndromes that are neither purely exterior nor purely interior, but rather present symptoms that are different from both.
Main symptoms: alternating chills and fever, chest and hypochondriac fullness, bitter mouth and dry throat, irritability, nausea, loss of appetite, and dizziness. The tongue tip is red, with a yellow-white coating, and the pulse is wiry.
Pathogenesis: The struggle between the righteous and pathogenic forces occurs in the half-exterior half-interior, leading to alternating chills and fever. The pathogenic factor affects the half-exterior half-interior, causing the gallbladder meridian to be affected, leading to fullness in the chest and hypochondrium, while heat in the gallbladder causes disharmony between the liver and stomach, resulting in irritability, dizziness, nausea, and loss of appetite.
Treatment principle: Harmonize and resolve both exterior and interior.
Common formula: Xiao Chai Hu Tang (Minor Bupleurum Decoction)
(4) Simultaneous Exterior and Interior Disease
This refers to the simultaneous presence of both exterior and interior syndromes at the same time. There are three common scenarios: 1) the initial onset of the disease presents both exterior and interior syndromes; 2) at the onset of the disease, only exterior syndromes are present, but as the pathogenic factor penetrates into the interior, interior syndromes appear while exterior syndromes remain unresolved; 3) the original disease has not yet resolved, and new exterior diseases occur, such as an original internal injury that is then affected by an external pathogenic factor, or an initial external disease that then causes dietary injury, which also falls under simultaneous exterior and interior disease. The treatment principle is to resolve both exterior and interior.
2. Cold and Heat
Cold and heat are two principles used to differentiate the nature of diseases, summarizing the conditions of yin and yang in the body. Generally, cold syndromes are manifestations of insufficient yang qi or the invasion of cold pathogenic factors, while heat syndromes are manifestations of excessive yang qi or the invasion of heat pathogenic factors. The saying goes, “Excessive yang leads to heat, excessive yin leads to cold; insufficient yang leads to cold, insufficient yin leads to heat.” Differentiating between cold and heat is the basis for using warming or cooling herbs in treatment, as the principle states, “Treat cold with heat, treat heat with cold.”
(1) Cold Syndrome
Cold syndrome is characterized by the invasion of cold pathogenic factors (such as cold or dampness) or the deficiency of yang qi and excess of yin, leading to weakened organ function and reduced activity. It can be divided into exterior cold syndrome and interior cold syndrome, with exterior cold syndrome already discussed. Here, we refer to interior cold syndrome.
Main symptoms: aversion to cold, cold limbs, no thirst or preference for hot drinks, pale complexion, cough with white phlegm, abdominal pain relieved by warmth, loose stools, and clear, frequent urination. The tongue is pale, with a white coating, and the pulse is deep and slow.
Pathogenesis: Yang deficiency and excess yin lead to cold symptoms, hence the aversion to cold and cold limbs. The spleen and stomach are cold, leading to abdominal pain relieved by warmth, and the pulse is deep and slow due to weak yang qi.
Treatment principle: Warm the middle and dispel cold.
Common formula: Fu Zi Li Zhong Tang (Aconite Decoction to Regulate the Middle)
(2) Heat Syndrome
Heat syndrome is characterized by the invasion of heat pathogenic factors (such as wind, heat, or fire) or excessive yang and deficiency of yin, leading to hyperactivity of organ function and increased activity. It can be divided into exterior heat syndrome and interior heat syndrome, with exterior heat syndrome already discussed. Here, we refer to interior heat syndrome.
Main symptoms: fever, no aversion to cold, irritability, thirst with a preference for cold drinks, red face and eyes, cough with yellow, thick phlegm, abdominal pain relieved by coolness, constipation, and short, red urination. The tongue is red, with a yellow coating, and the pulse is rapid.
Pathogenesis: Excessive yang leads to fever and a preference for coolness, heat damages body fluids, leading to thirst, and heat causes short, red urination and constipation. The rapid pulse indicates excessive heat.
Treatment principle: Clear heat.
Common formula: Bai Hu Tang (White Tiger Decoction)
(3) Excess Heat and Deficiency Heat
The clinical manifestations and treatment principles of excess heat syndrome caused by the invasion of heat pathogenic factors differ from those of deficiency heat syndrome caused by the deficiency of yin fluids or hyperactivity of organ function. The following table summarizes the differences.

(4) True Cold and False Heat
In critical stages of disease development, one may observe phenomena such as “true cold appearing as heat” or “true heat appearing as cold.” Clinically, a syndrome that is essentially heat but presents with cold symptoms is termed “true heat, false cold,” while a syndrome that is essentially cold but presents with heat symptoms is termed “true cold, false heat.” This situation often indicates a severe disease. If the essence is not grasped, one may be misled by the false appearance, leading to misdiagnosis and mistreatment.
1. “True Cold, False Heat”: For example, patients with chronic wasting diseases often present with body heat, flushed cheeks, restlessness, black tongue coating, and a floating pulse. On the surface, this appears to be a heat syndrome, but the patient prefers warmth, appears listless and apathetic, curls up while lying down, has a pale tongue, moist black coating, and a floating but weak pulse. This indicates that yin is excessive internally, constraining yang externally, and the essence is still a cold syndrome, hence termed “true cold, false heat.” Treatment should focus on warming the interior and restoring yang.
2. “True Heat, False Cold”: This refers to a true heat syndrome presenting with false cold symptoms, such as in severe heat-related illnesses where patients may appear indifferent, lethargic, and have cold hands and feet, with a deep and thin pulse. On the surface, this seems like a cold syndrome, but there are signs of heat in the mouth and nose, burning sensations in the chest and abdomen, thirst with a preference for cold drinks, constipation, and short, red urination. The tongue is red, with a yellow, dry coating, and the pulse is thin and rapid but forceful. This indicates that internal heat is constrained and cannot express outwardly, and the essence is a heat syndrome, hence termed “true heat, false cold.” Treatment should focus on clearing internal heat and promoting yang qi.
Generally, the manifestations of cold and heat are superficial, while the internal conditions of cold and heat represent the essence.
Differentiating between cold and heat syndromes should not be based on isolated symptoms or signs but should involve a comprehensive observation of the entire disease presentation, especially the aspects of cold and heat, thirst or lack thereof, complexion, temperature of the limbs, urination, tongue appearance, and pulse characteristics. For instance, aversion to cold and preference for warmth indicates cold, while fever, aversion to heat, and preference for cold indicate heat; a lack of thirst indicates cold, while thirst with a preference for drinking indicates heat; a red complexion indicates heat; cold hands and feet indicate cold, while warm limbs indicate heat; clear, frequent urination and loose stools indicate cold, while short, red urination and constipation indicate heat; a pale tongue with a white coating indicates cold, while a red tongue with a yellow coating indicates heat, etc. From the comparison of cold and heat syndromes, it can be seen that cold syndromes are associated with excess yin and often co-occur with yang deficiency, while heat syndromes are associated with excess yang and often present with signs of yin fluid deficiency.
3. Deficiency and Excess
Deficiency and excess are two principles used to differentiate the strength of the body’s righteous qi and the severity of pathogenic factors. Generally, deficiency refers to insufficient righteous qi, and deficiency syndromes are manifestations of this insufficiency, while excess refers to excessive pathogenic qi, and excess syndromes are manifestations of this excess. The Suwen states, “When pathogenic qi is strong, it is excess; when essence is depleted, it is deficiency.” From the perspective of the comparative strength of the righteous and pathogenic forces, deficiency syndromes indicate insufficient righteous qi, while pathogenic qi is not strong; excess syndromes indicate excessive pathogenic qi, but righteous qi is still present, reflecting a fierce struggle between the righteous and pathogenic forces. Differentiating between deficiency and excess is the basis for determining whether to tonify the righteous (nourish deficiency) or drain the pathogenic (reduce excess), as the principle states, “Tonify the deficient, drain the excess.”
(1) Deficiency Syndrome
Deficiency syndromes can arise from a weak constitution (either congenital or acquired), prolonged illness damaging the righteous qi, excessive blood loss, loss of essence, profuse sweating, or invasion of external pathogenic factors that damage the righteous qi.
Main symptoms: pale or sallow complexion, listlessness, fatigue, palpitations, shortness of breath, cold limbs, or five hearts heat, spontaneous sweating, night sweats, loose stools, frequent urination, pale tongue with little or no coating, and weak pulse.
Clinically, deficiency syndromes can be categorized into qi deficiency, blood deficiency, yin deficiency, and yang deficiency, with organ-specific deficiencies (such as lung qi deficiency, heart blood deficiency, liver yin deficiency, spleen qi deficiency, kidney yang deficiency, etc.) discussed in organ differentiation.

From the above table, it can be seen that qi deficiency and yang deficiency both indicate insufficient yang qi, hence their clinical presentations are similar, with symptoms such as pale complexion, fatigue, and spontaneous sweating. However, they differ in that qi deficiency does not present with cold symptoms, while yang deficiency does present with cold symptoms—aversion to cold, cold limbs, and slow pulse. Blood deficiency and yin deficiency both indicate insufficient yin fluids, hence their clinical presentations are similar, with symptoms such as weight loss, dizziness, palpitations, and insomnia. However, they differ in that blood deficiency does not present with heat symptoms, while yin deficiency presents with heat symptoms due to the inability of yin fluids to restrain yang qi, leading to symptoms such as low fever or tidal fever, dry mouth, and dry throat.
(2) Excess Syndrome
Excess syndromes can arise from a robust constitution where external pathogenic factors invade acutely, or from dysfunction of the organs leading to the accumulation of pathological products within the body, such as qi stagnation, blood stasis, phlegm-damp accumulation, parasitic accumulation, or food stagnation.
Clinical manifestations vary based on the nature of the pathogenic factors and the organs affected, characterized by excessive pathogenic qi and weakened righteous qi, with a fierce struggle between the two. Common symptoms include high fever, flushed face, irritability, delirium, loud voice, abdominal distension and pain that resists pressure, excessive phlegm, constipation, poor urination, or the presence of blood stasis, edema, food stagnation, or parasitic accumulation, with thick, greasy tongue coating and a forceful pulse.
Treatment principle: Drain excess and attack the pathogenic factors is the main method for treating excess syndromes, as the principle states, “Excess should be drained.” However, different methods such as clearing heat, promoting bowel movements, draining water, resolving phlegm, regulating qi, invigorating blood, and eliminating parasites will be discussed in relevant chapters.
Differentiating between deficiency and excess syndromes can be considered from the following aspects:
1) Onset time: new or acute diseases with a short duration are often excess syndromes, while chronic or long-standing diseases are often deficiency syndromes;
2) Etiology: external pathogenic factors often lead to excess syndromes, while internal injuries often lead to deficiency syndromes;
3) Constitution: younger, robust individuals are more likely to present with excess syndromes, while older, weaker individuals are more likely to present with deficiency syndromes;
4) Clinical symptoms and signs: refer to the following table for differentiation.

4. Yin and Yang
Yin and yang are two principles used to differentiate the nature of diseases, serving as the overarching principles of the Eight Principles. They summarize the concepts of exterior and interior, cold and heat, deficiency and excess. The “Liu Jing” states, “In human diseases, there must be a basis, either based on yin or based on yang. Although the manifestations of diseases are numerous, their essence is one,” indicating that although syndromes may be complex and variable, they ultimately fall into two categories: yin and yang. Therefore, the key to diagnosing diseases is to first determine whether they belong to yin or yang. Generally, exterior, excess, and heat syndromes belong to yang syndromes, while interior, deficiency, and cold syndromes belong to yin syndromes. However, clinically, yin syndromes often refer to interior deficiency cold syndromes, while yang syndromes often refer to interior excess heat syndromes.
(1) Yin Syndrome
Yin syndrome is characterized by deficiency of yang qi and excess of yin within the body. Generally, yin syndromes present with cold symptoms, such as aversion to cold, absence of fever, cold limbs, listlessness, and a slow or weak pulse. They arise from weakened organ function and reduced bodily responses, often seen in older, weaker individuals or those with chronic illnesses, presenting a picture of deficiency and cold.
(2) Yang Syndrome
Yang syndrome is characterized by excess of yang qi and preservation of righteous qi within the body. Generally, yang syndromes present with heat symptoms, such as fever, aversion to heat, warm limbs, irritability, thirst, and a rapid pulse. They arise from hyperactivity of organ function and are often seen in robust individuals or in the early stages of diseases, presenting a picture of excess heat.
The main clinical manifestations of yin and yang syndromes can be referenced in the following table:

3. Loss of Yin and Loss of Yang
Loss of yin and loss of yang are two dangerous syndromes that can occur during the disease process, often seen in cases of high fever, profuse sweating, severe vomiting and diarrhea, or excessive blood loss, leading to rapid loss of yin fluids or yang qi. Although loss of yin and loss of yang are both classified as deficiency syndromes, they are distinct from general deficiency syndromes due to their special and critical nature.
Clinical manifestations of loss of yin and loss of yang, in addition to various critical symptoms of the underlying disease, often present with varying degrees of sweating. However, the sweating in loss of yin is hot and sticky, often accompanied by hot skin, warm hands and feet, thirst with a preference for cold drinks, red tongue with a dry coating, and a rapid, weak pulse, indicating depletion of yin and extreme yang; while the sweating in loss of yang is profuse and cool, often accompanied by aversion to cold, lethargy, cold limbs, and a weak pulse, indicating loss of yang and excess yin.
Due to the interdependence of yin and yang, depletion of yin fluids leads to the dispersion of yang qi, while depletion of yang qi leads to the inability of yin fluids to generate, resulting in the clinical manifestations of loss of yin and loss of yang being difficult to distinguish. They can rapidly transform into one another, with differences in priority and sequence.
The treatment for both loss of yin and loss of yang focuses on tonifying the righteous qi and stabilizing the condition. For loss of yin, the approach is to tonify qi, restrain yin, and generate fluids, with common formulas such as Sheng Mai San (Generate the Pulse Powder); for loss of yang, the approach is to tonify qi, stabilize the condition, and restore yang, with common formulas such as Du Shen Tang (Ginseng Decoction) and Shen Fu Tang (Ginseng and Aconite Decoction).
The differentiation of loss of yin and loss of yang can be referenced in the following table:

5. Interrelationships and Application of the Eight Principles
The distinctions between exterior and interior, cold and heat, deficiency and excess, and yin and yang are not merely isolated, static, or unchanging; they are complex, interrelated, and capable of transformation. In summary, the Eight Principles exhibit relationships of “coexistence,” “mixing,” and “transformation.”
(1) Coexistence
“Coexistence” refers to the simultaneous appearance of symptoms from two or more principles. For example, in the early stages of an externally contracted heat disease, one may observe exterior symptoms while further differentiating between cold or heat, leading to classifications of exterior cold or exterior heat syndromes. In cases of prolonged illness, deficiency syndromes may also need to be differentiated into deficiency cold or deficiency heat syndromes. The appearance of coexisting syndromes should not be treated equally; rather, there is a primary and secondary relationship. For instance, both exterior cold and exterior heat syndromes are primarily exterior syndromes, with cold or heat being secondary to the exterior syndrome, thus treatment should primarily focus on releasing the exterior, using either warm acrid herbs or cool acrid herbs accordingly. Similarly, deficiency cold and deficiency heat syndromes are primarily deficiency syndromes, with cold or heat being secondary, thus treatment should primarily focus on tonifying deficiency, using either warming or nourishing methods. When exterior and interior syndromes coexist, the primary syndrome should be determined based on the specific clinical situation.
(2) Mixing
“Mixing” refers to the simultaneous presence of opposing symptoms from two principles, such as cold-heat mixing, deficiency-excess mixing, or exterior-interior mixing (commonly referred to as simultaneous exterior and interior disease). Additionally, during the progression of a disease, false appearances may arise, such as true heat appearing as cold or true cold appearing as heat. Therefore, during the diagnostic process, careful observation and comprehensive analysis are essential to eliminate falsehoods and retain the truth, grasping the essence to avoid misdiagnosis and mistreatment, which could delay treatment.
(3) Transformation
“Transformation” refers to the phenomenon where symptoms of one principle transform into those of the opposing principle. The relationships between exterior and interior, cold and heat, deficiency and excess, and yin and yang are not only opposing but can also transform into one another under certain conditions. For example, an exterior cold syndrome presenting with aversion to cold and fever may, due to disease progression or improper treatment, lead to the pathogenic factor penetrating into the interior, resulting in a transformation from exterior cold syndrome to interior heat syndrome. Excess syndromes may transform into deficiency syndromes due to misdiagnosis or inadequate treatment, where the pathogenic qi gradually diminishes but the righteous qi is also harmed, leading to a gradual transformation into deficiency syndromes. Conversely, deficiency syndromes may give rise to excess syndromes due to insufficient righteous qi, leading to the accumulation of phlegm, dampness, qi stagnation, or blood stasis, resulting in various excess syndromes. Transformation occurs under specific conditions, and during diagnosis, it is crucial to continuously observe changes in the pathogenesis, diagnose and treat promptly to prevent the disease from worsening and to promote recovery.
The application of the Eight Principles in diagnosis begins with differentiating between exterior and interior to determine the location of the disease; then differentiating between cold and heat, deficiency and excess to clarify the nature of the disease and understand the comparative strengths of the righteous and pathogenic forces; finally, summarizing the findings using the yin and yang principles.
Summary
The Eight Principles of Diagnosis is a method of summarizing and analyzing diseases from the perspectives of exterior and interior, cold and heat, deficiency and excess, and yin and yang. Although it should be combined with etiology diagnosis, defensive qi, nutritive qi, and blood diagnosis for a more comprehensive understanding, it serves as the foundation for various diagnostic methods, simplifying complex presentations and providing a framework for understanding.
The Eight Principles are not static but can transform under certain conditions; exterior syndromes can progress to interior syndromes as the disease worsens, while interior syndromes can resolve and present as exterior syndromes as the condition improves. Heat syndromes can transform into cold syndromes, and excess syndromes can transform into deficiency syndromes, often indicating a gradual recovery of righteous qi.
Although the Eight Principles have distinct presentations, they rarely exist in isolation; rather, they exhibit complex relationships of coexistence and mixing, and may sometimes present false appearances. Therefore, during the diagnostic process, it is essential to conduct thorough investigations, maintain continuity in thought, and discern the essence through observation, ensuring accurate analysis and diagnosis for appropriate treatment.