Etiology is defined as various kinds of factors that cause diseases. As TCM sees it, etiology mainly includs the six exogenous pathogens, pestilence,(epidemic pathogenc factors ) the seven emotions, emotional frustration, improper diet, overwork, maladjustment between work and rest, traumatic injuries, insect or animal bites, phlegm retention, blood stasis, etc. Zhang ZhongJing of the Eastern Han Dynasty pointed out: "Despite numerous diseases, they would not exceed three categories". Up to the Song Dynasty, Chen Wuze put forward the theory of the three categories of etiologic factors i. e., exogenous pathogenic factors, endogenouspathogenic factors and non-endo-exogenous pathogenic factors. To be more specific, six pathogenic factors invading the body from the outside pertain to exogenous pathogenic factors; the seven emotions directly involving the internal organs are attributed to endogenous pathogenic factors; other pathogenic factors, such as improper diet, overwork, traumatic injury, insect and animal bites, etc. , are said to be non-endo-exogenous pathogenic factors. "The theory of the three categories of etiologic factors" caused strong repercussions in later ages and promoted the research into the etiology.|
In discerning etiology, besides having a sound knowledge of the objective conditions that possibly lead to illness, TCM centers attention on the clinical manifestations of diseases, and inquires into the etiology through analyzing the symptoms and signs so that a basis for treatment and medications may be is provided. This method is called "seeking cause of disease through differentiation of syndromes."The six exogenous factors are a general term for wind, cold, summer-heat, damp, dryness and fire. Under normal conditions, they are six climatic factors. TCM calls them the "six qi." They are not harmful to human beings but rather are the essential conditions of the growth of all living things in nature. Thus, the six qi will not cause diseases normally. However, when the six qi become too excessive or deficient, or when the body's resistance is too weak to adapt itself to the abnormal changes, the six qi will be changed into the pathogenic factors to attack the human body and cause diseases. They, as such, are known as "six exogenous pathogens" (liu yin). Of the six exogenous pathogens the five result from the dysfunction of the zang-fu organs rather than the exogernous factors invading the body from the outside though they also have the symptoms similar to wind, cold, dampness, dryness and fire.(Of...是介词短语提前。前置同倒装等一样，是强化信息的重要手段之一。有如：a. Of the two the latter is far better than the former. b. Of the 100 cases treated with this therapy, 60 are male and 40 female. ) In order to distinguish them from the six exogenous pathogens, they are termed the "five endogenous pathogens", i.e., the endogenous wind,endogenous cold, endogenous dampness, endogenous dryness and endogenous fire.
The pathogenic features of the six exogenous pathogens are as follows. 六淫的病理特征如下：
(l) The six exogenous pathogens have close relationships with the seasonal changes and living environment. For example, diseases caused by wind-pathogen mostly occur in spring; summer-heat diseascs usually appear in summer; damp diseases often happen in later summer, dry diseases arise most often in autumn and cold diseases are often seen in winter. And the people who live in damp circumstances are susceptible to damp diseases, while the people living under a high temperature are liable to contract fire or dryness diseases. (1)六淫与季节变化和生活环境有密切关系。例如，风邪致病多在春季；暑邪致病通常在夏季；暑邪致病通常发生在夏至后；燥邪致病多在秋季；寒邪致病见于冬季。生活在潮湿环境的人易感受湿邪，而生活在高温环境下的人则易感染火邪或燥邪。
(2) The six exogenous pathogens may singly invade the body by a single pathogen and simultaneously and invade the body by more than two pathogen. For example, common cold results frequently from pathogenic wind and cold; diarrhea is caused by pathogenic dampnese and heat; bi-syndrome (arthralgia) is causcd by pathogenic wind, cold and dampness and so on. (2)六淫可以单独侵犯人体也可两种以上同时侵犯人体。例如，普通感冒通常由风寒之邪所致；泻泄由湿热之邪所致；风寒湿夹杂而致痹症等。
(3) They may be transformed into each other. Examples are: pathogenic cold in the body may be transformed into heat and prolonged summer-heat dampness may bring about dryness and fire to impair yin. (3)六淫之间可以互相转化。例如，体内寒邪可化热，暑湿可以化火化燥伤阴。
(4) The last featurc of the six exogenous pathogens is that they invade the human body via the body surface or from the mouth and nose or through both concurrently. This is known as"affection resulting from six exogenous pathogens." (4)六淫的最后一个特点是它们可以由体表或口鼻或同时侵犯人体。这就是“外感六淫”。
The seven emotions refer to the human mental activities. In TCM, they are classified into seven classes: joy, anger, melancholy, anxiety, grief, fear and terror.They are the different responses to the environmental stimuli in the human body in general circumstances, they belong to the normal physiological activities and will not cause diseases. When sudden, strong,long or protracted (prolonged)emotional stimuli go beyond the body's adaptability and endurance, the emotional stimuli will become pathogenic factors, which cause dysfunction of qi, blood and the zang-fu organs and imbalance of yin and yang, hence leading to diseases. This is known as "internal injury caused by the seven".
The seven emotions are different from the six exogenous pathogens in causing diseases. The six exogenous pathogens, as mentioned ahove, usually invade the body through the skin, mouth and nose, and it is mostly exterior syndromes at the early stage of the onset. The seven emotions, however, directly affect the corresponding zang-fu organs to bring on diseases because a certain zang-fu organ is closely related to a certain emotional activity. (不定式短语 to bring on ... 在句中作结果状语。又如：a. Arthur returned home to be struck by another blow. b. What have I done to deserve so much? c. He made a long speech only to show his ignorance of the subject. )So TCM says, "Anger impairs the liver; excessive joy impairs the heart; grief or melancholy impairs the lung, anxiety impairs tbe spleen, and fright or fear impairs the kidney", The abnormal emotions mainly influence qi activity of the internal organs, so as to cause the dysfunction in ascending and descending of qi. Concretely speaking, "Anger causes the qi (to the liver)to ascend: joy makes the qi (of the heart) sluggish; sorrow makes the qi (of the lung) consumed; fear induces the qi (ofthe kidney) to dissipate; fright causes the disorder of the qi (of the heart) ; and anxiety brings about the depression of the qi (of the spleen)." As concerns other pathogenic factors such as pestilence, improper diet, maladjustment of work and rest, parasites, surgical trauma, phlegm retention, blood stasis, etc,we have to, though they are of equal importance, give them upon account of limited space.
Special phrases 特殊短语
1.Pathogenic factors; pathogens 1.邪气
2.exogenous pathogenic factors; (exogenous pathogenic) 2.外邪
3.seasonal pathogenic factors (seasonal pathogens) 3.时邪
4.pathogenic wind 4.风邪
5.endogenous wind 5.内风
6.exogenous wind 6.外风
7.Wind is the first and foremost factor to cause various diseases 7.风为百病之长
8.Sudden spasm and rigidity of muscles result from wind. 8.诸暴强直，皆属于风
9.Vomiting with sour vomitus of spouting diarrhea with tenesmus is caused by wind. 9. 诸病吐酸，暴注下迫，皆属于热。
10.Abdominal distension is mainly related to heat 10.诸胀腹大，皆属于热
11.visible phlegm 11.有形之痰
12.invisible phlegm 12.无形之痰
13.excess of sexual intercourse 13.房劳过度