Concept of Disease (症. 病. 证的关系)

In general, disease is perceived as a disharmony (or imbalance) in the functions or interactions of yin, yang, qi, xuĕ, zàng-fǔ, meridians etc. and/or of the interaction between the human body and the environment.

Therapy is based on which "pattern of disharmony" can be identified. Thus, "pattern discrimination" is the most important step in TCM diagnosis. It is also known to be the most difficult aspect of practicing TCM. In order to determine which pattern is at hand, practitioners will examine things like the color and shape of the tongue, the relative strength of pulse-points, the smell of the breath, the quality of breathing or the sound of the voice. For example, depending on tongue and pulse conditions, a TCM practitioner might diagnose bleeding from the mouth and nose as: "Liver fire rushes upwards and scorches the Lung, injuring the blood vessels and giving rise to reckless pouring of blood from the mouth and nose.". He might then go on to prescribe treatments designed to clear heat or supplement the Lung.

In TCM, a disease has two aspects: "bìng" and "zhèng". The former is often translated as "disease entity", "disease category", "illness", or simply "diagnosis". The latter, and more important one, is usually translated as "pattern" (or sometimes also as "syndrome"). For example, the disease entity of a common cold might present with a pattern of wind-cold in one patient, and with the pattern ofwind-heat in another.

Disease entities

From a scientific point of view, most of the disease entitites (病, pinyin: bìng) listed by TCM constitute mere symptoms. Examples include headache, cough, abdominal pain, constipation etc.

Since therapy will not be chosen according to the disease entity but according to the pattern, two patients with the same disease entity but different patterns will receive different therapy. Vice versa, patients with similar patterns might receive similar therapy even if their disease entities are different. This is called 异病同治，同病异治 (pinyin: yì bìng tóng zhì, tóng bìng yì zhì, "different diseases, same treatment; same disease, different treatments").

Patterns 

In TCM, "pattern" (证, pinyin: zhèng) refers to a "pattern of disharmony" or "functional disturbance" within the functional entities the TCM model of the body is composed of. There are disharmony patterns of qi, xuě, the body fluids, the zàng-fǔ, and the meridians. They are ultimately defined by their symptoms and "signs" (i.e., for example, pulse and tongue findings).

In clinical practise, the identified pattern usually involves a combination of affected entities (compare with typical examples of patterns). The concrete pattern identified should account for all the symptoms a patient has.