Having learned the healthy body — its substances, organs and channels — we now ask the next question: why does illness begin? Chinese medicine has a clear and rational theory of the causes of disease, and understanding it is the bridge between knowing the healthy body and being able to treat the sick one. This course maps the causes; this first lesson gives the framework that organises them all.
The contest: Upright Qi versus pathogenic factor
Underlying the whole theory is a single, powerful idea: disease arises from a contest between two forces.
- On one side stands the Upright Qi (Zheng Qi) — the body's own healthy Qi, its vitality and resistance, its capacity to defend itself and maintain balance. This includes the Defensive Qi guarding the surface and the general strength of the organs and substances.
- On the other stands the pathogenic factor (Xie Qi, the "evil Qi") — any influence that disturbs the balance, whether it invades from outside or arises within.
Disease occurs when the pathogenic factor overcomes the Upright Qi. Two great principles follow from this, and they run through all of Chinese medicine:
"When the Upright Qi is strong within, pathogens cannot invade." "Where a pathogen lodges, the Qi there must be weak."
This means illness is never only about the pathogen. It is always about the relationship between the strength of the body and the strength of the challenge. A strong person may resist a cold that lays a weak person low. This is why Chinese medicine attends so much to strengthening the Upright Qi — supporting the body's own resistance — as well as to expelling pathogens, and why prevention (a strong constitution, good habits) is treated as the deepest medicine.
The three categories of cause
The classical tradition sorts the causes of disease into three great categories, a scheme that has organised Chinese pathology for many centuries:
- External causes — the six external (climatic) pathogenic factors: Wind, Cold, Summer-Heat, Damp, Dryness and Fire. These are influences from the environment that invade the body from the outside, usually attacking the exterior first. They cause the externally-contracted illnesses — colds, flus, and many acute conditions.
- Internal causes — the seven emotions: joy, anger, worry, pensiveness, grief, fear and fright. When excessive, prolonged or sudden, the emotions disturb the Qi and injure the organs from within. These are among the most important causes of chronic internal disease.
- Causes that are "neither external nor internal" — a third group covering everything else: diet (improper eating), overwork and excessive rest, excessive sexual activity, physical trauma, bites and poisons, and the pathological products (like Phlegm and Blood stasis) that, once formed, become causes of further disease.
Why the framework matters
This three-part scheme is not just a tidy list; it directly shapes diagnosis and treatment. When a physician traces a complaint back to its cause, they ask: did this come from outside (a climatic invasion), from within (the emotions), or from the manner of living (diet, overwork, trauma)? The answer points toward the pattern and the treatment. An externally-caused cough is treated very differently from one rooted in weak Lungs and grief.
In the lessons ahead we take each category in turn — first the six external pathogens and their distinctive natures, then the seven emotions and their effects on the organs, then diet, lifestyle, and the secondary pathogens Phlegm and Blood stasis. Throughout, hold the founding idea: disease is a contest between the body's Upright Qi and a pathogenic challenge, and to understand any illness you must weigh both the strength of the challenge and the strength of the body that meets it.
