---
title: "The eight principles"
url: "https://acuiq.com/wiki/theory/the-eight-principles"
updated: 2026-10-12
last_verified: 2026-10-12
license: CC-BY-4.0
license_url: "https://creativecommons.org/licenses/by/4.0/"
section: "theory"
basis: "Classical and modern"
audience: "Anyone"
published: "2026-10-12"
reading_minutes: 9
sources: 8
---

# The eight principles

_Interior and exterior, cold and heat, deficiency and excess, yin and yang: how the WHO terminologies define the four pairs, where the scheme came from, and what agreement studies have measured._

The eight principles, _ba gang_ (八綱), are four pairs of opposites that Chinese medicine uses to make the first, broadest sort of a patient’s findings: exterior and interior, cold and heat, deficiency and excess, and yin and yang. The WHO’s [2007 standard terminology for traditional medicine in the Western Pacific](https://iris.who.int/handle/10665/206952) defines them as the guiding principles of pattern identification, and defines pattern identification as the analysis of clinical data to determine the location, cause and nature of a patient’s disease. Its successor, the [2022 WHO terminology for traditional Chinese medicine](https://iris.who.int/handle/10665/352306), defines eight principle pattern differentiation as sorting the data from the four diagnostic methods into the eight patterns, with the analysis focused on the location of the disease, its nature, and the relative strength of the body’s anti-pathogenic qi and the pathogenic factors. Exterior and interior answer the first question, cold and heat the second, deficiency and excess the third, and yin and yang group the answers; the more specific methods of differentiation build on them. [Patterns, symptoms and what you can look up](/wiki/theory/patterns-and-symptoms) explains why a pattern, rather than the complaint, is what a classical prescription is written against.

## The four pairs

The 2007 terminology gives each pair its own method of identification and defines what that method decides.

| Pair | Chinese | What the method decides |
| --- | --- | --- |
| Exterior and interior | 表裏 | The location of the disease: in the exterior or the interior, seated superficially or deeply |
| Cold and heat | 寒熱 | The nature of the disease, by categorising the symptoms as cold or heat |
| Deficiency and excess | 虛實 | The nature of the disease, by comparing the strength of the healthy qi with that of the pathogenic qi |
| Yin and yang | 陰陽 | Which group a pattern belongs to: interior, cold and deficiency patterns are yin; exterior, heat and excess patterns are yang |

### Exterior and interior

The 2007 terminology defines an exterior pattern as one occurring chiefly at the early stage of an externally contracted illness, with sudden onset, aversion to cold or wind, fever, headache, generalised pain, a thin tongue coating and a floating pulse. An interior pattern is a general term for disease inside the body: in the organs, in the qi and blood, or in the bone marrow. Between the two it defines a half-exterior half-interior pattern, marked by fever and chills that alternate, a full, choking feeling in the chest and ribs, a bitter taste and a pulse it calls string-like. The external contractions are the climatic factors described in [Causes of disease](/wiki/theory/causes-of-disease).

### Cold and heat

In the 2007 definitions a cold pattern arises from an external cold pathogen or from insufficient yang within the body, and is commonly shown by aversion to cold, no thirst, thin clear sputum, long voidings of clear urine, loose bowels, a pale tongue with a white coating, and a tight or slow pulse. A heat pattern arises from an attack of external heat or a prevalence of yang qi, and is usually shown by fever, thirst, a flushed face, irritability, thick yellow sputum, short voidings of dark urine, constipation, a red tongue with a yellow coating and a rapid pulse. The terminology also defines patterns in which the two mix, such as heat above with cold below.

### Deficiency and excess

The 2007 terminology defines a deficiency pattern as one caused by a deficiency of the healthy qi, and names four kinds: of yin, yang, qi and blood. An excess pattern is caused by external pathogenic factors, among them the six excesses, pestilential pathogens, worms and toxins, or by products that accumulate when the organs fail, which it lists as phlegm, retained fluid, water, dampness, pus, static blood and retained food. A deficiency-excess complex pattern is the case where both exist at once. The 2022 edition puts the pair in one sentence: excess means exuberant pathogenic factors, and deficiency means insufficient anti-pathogenic qi.

### Yin and yang

Yin and yang are the two headings under which the other six sit, and the 2007 terminology defines yin-yang pattern identification as that grouping. [Yin and yang](/wiki/theory/yin-and-yang) gives the WHO’s description of each group’s manifestations and the theory behind the pair.

## How the pairs combine

A pattern is usually a position on several pairs at once. The 2022 terminology defines concurrent patterns and gives exterior deficiency, exterior cold, interior excess and interior deficiency cold as examples. The 2007 terminology names some combinations as patterns in their own right: deficiency cold, a cold pattern arising from deficient yang qi, which it calls the same as the yang deficiency pattern; and deficiency heat, a heat pattern caused by deficiency of yin, qi, blood or fluids.

The terminologies also define cases where the pairs are read against the surface. In the 2007 definitions, true cold with false heat arises when exuberant internal cold forces yang qi outward: the patient has a flushed face, agitation and thirst, while the chest and abdomen are cool to the touch and the limbs cold. True heat with false cold is the reverse, with cold limbs and shivering alongside high fever, a chest and abdomen hot to the touch, and a red tongue with a dry yellow coating. The 2022 edition adds cold-heat transformation, in which a cold pattern turns into heat or a heat pattern into cold, and lists overuse of warming or cooling medicines among the contributing factors.

The same words do not always mean the same thing across the traditions the 2007 terminology covers. Its entry for the yin deficiency pattern adds that Kampo, the Japanese tradition, understands the term as a yin pattern combined with a deficiency pattern, and its entry for the yang deficiency pattern says Kampo understands that term as a yang pattern combined with an excess pattern.

## Where the scheme sits among the methods

The 2007 terminology sets out pattern identification in nine sections of its diagnostics chapter, and puts the eight principles first. The others cover identification by cause of disease, by qi and blood, by fluids, by the organs (the viscera and bowels of its translation, the zang-fu), by the six meridians, by the four levels of defence, qi, nutrient and blood, and by the triple energizer, with a section of various other patterns. Their definitions show their reach. Visceral identification categorises patterns by the pathological changes of the organs, which [The zang-fu organs](/wiki/theory/the-zang-fu-organs) describes. Six-meridian identification is applied to acute febrile diseases at their different stages, and the terminology adds that it is also useful for other diseases. The four-level method categorises epidemic febrile diseases, with the four levels marking stages in the clinical course. [The six stages and the four levels](/wiki/theory/six-stages-and-four-levels) sets out both methods and the triple-energizer method beside them. The 2022 terminology defines the whole of treatment based on pattern differentiation as analysing the findings according to the eight principles, the zang-fu organs, aetiology and pathogenesis.

A 2013 comparative study by [Kim Jin-Ho in the Journal of Korean Medical Classics](https://doi.org/10.14369/skmc.2013.26.2.047) describes eight principle identification as the base of the other methods. Reading three Ming and Qing physicians, it concludes that findings should be sorted in the order exterior-interior, cold-heat, deficiency-excess, and then summarised as yin or yang.

## Where the scheme came from

The sources disagree on how old the scheme is. Heiner Fruehauf, [introducing his translation](https://classicalchinesemedicine.org/han-fa-the-sweating-diaphoretic-method/) of a chapter by the Qing physician Cheng Guopeng, describes Cheng’s _Yixue xinwu_ (醫學心悟, translated as Enlightened Insights into the Science of Medicine) of 1732 as the book that first spelled out the eight parameters, together with eight methods of treatment, and says the eight parameters have since become the standard diagnostic parameters of Chinese medicine. Kim’s study compares the chapter of Cheng’s book on cold, heat, deficiency, excess, exterior, interior, yin and yang with an earlier treatment of the same pairs in the _Jingyue quanshu_ of the Ming physician Zhang Jiebin, whose chapters on yin and yang, the six changes, exterior and interior patterns, deficiency and excess, and cold and heat it reads alongside, and with the _Bihua yijing_ of Jiang Hantun.

Charles Buck, in [an article in the Journal of Chinese Medicine](https://www.journalofchinesemedicine.com/who-invented-bagang.html), takes the account further back. Its abstract describes bagang as possibly the dominant style of pattern differentiation in contemporary Chinese medicine, rejects the view that it is a 20th-century invention of the Chinese communists, and argues that it has been part of Chinese medicine since Han and pre-Han times.

## Agreement on the pairs

Studies of whether practitioners reach the same overall pattern for the same patient are collected in [The four examinations](/wiki/theory/the-four-examinations), which reports low to moderate agreement. A few studies have measured the eight-principle pairs on their own.

A 2021 study at Keio University by [Maeda-Minami and colleagues](https://doi.org/10.1089/acm.2020.0298) had three Kampo specialists assess the same 64 patients from written records, a 140-item symptom questionnaire with blood pressure, age, sex, height and weight, rather than in person. Each specialist rated deficiency-excess on three levels (excess, medium, deficiency) and cold-heat on four (cold, intermediate, heat, mixed). On deficiency-excess they reached 85.9% weighted agreement, with a Gwet’s agreement coefficient of 0.708; on cold-heat, 64.6% agreement and a coefficient of 0.542. Gwet’s coefficient discounts the agreement expected by chance, as kappa does, and the authors chose it because the categories are not equally common. On a third axis, qi, blood and fluids, with seven categories, agreement fell to 35.9%.

A 2021 pilot study in Korea by [Choi and colleagues](https://doi.org/10.13048/jkm.21001) compared in-person pattern identification by three Korean medicine doctors, in 16 people with cancer, with their identification from questionnaire, tongue-image and pulse-analyser data alone. Kappa between the two was 0.455 for cold or not cold and 0.429 for heat or not heat. It could not be calculated for deficiency or excess: in person, 14 of the 16 were judged deficient and none excess, which left too few cases on one side.

Questionnaires have been built to make the cold-heat judgement more repeatable. A 2010 study by [Ryu and colleagues](https://doi.org/10.1089/acm.2009.0331) tested a 20-item cold-heat questionnaire on two groups of 63 and 64 hospital patients, each classified by a doctor as cold, heat or mixed, and reported that it matched the doctor’s classification in 94.9% and 92.3% of cases. That measures agreement between an instrument and one doctor, not between practitioners.

## What AcuiQ records

Several eight-principle terms are in AcuiQ’s index because published prescriptions or point indication lists used them, among them [deficiency](/symptoms/deficiency), [excess](/symptoms/excess), [heat](/symptoms/heat), [yin deficiency](/symptoms/yin-deficiency), [yang deficiency](/symptoms/yang-deficiency) and [qi deficiency](/symptoms/qi-deficiency). A prescription filed under one of them records the pattern its authors reached. AcuiQ does not check the differentiation behind it, and the agreement studies above cannot say whether another practitioner would have placed the same patients on the same side of each pair.

### Sources

1. WHO Regional Office for the Western Pacific, WHO international standard terminologies on traditional medicine in the Western Pacific Region, 2007 — https://iris.who.int/handle/10665/206952
2. World Health Organization, WHO international standard terminologies on traditional Chinese medicine, 2022 — https://iris.who.int/handle/10665/352306
3. Kim Jin-Ho, A comparative research of eight principle pattern identification, based on Zhang Jie-Bin, Cheng Guo-Peng and Jiang Han-Tun, Journal of Korean Medical Classics 26(2):47-59, 2013 — https://doi.org/10.14369/skmc.2013.26.2.047
4. Cheng Guopeng, Han fa: the sweating (diaphoretic) method, translated and introduced by Heiner Fruehauf, ClassicalChineseMedicine.org — https://classicalchinesemedicine.org/han-fa-the-sweating-diaphoretic-method/
5. Charles Buck, Who invented bagang?, Journal of Chinese Medicine (abstract) — https://www.journalofchinesemedicine.com/who-invented-bagang.html
6. Maeda-Minami A, Yoshino T, Horiba Y, Nakamura T, Watanabe K, Inter-rater reliability of Kampo diagnosis for chronic diseases, Journal of Alternative and Complementary Medicine 27(7):613-616, 2021 — https://doi.org/10.1089/acm.2020.0298
7. Choi Y, Kim SD, et al., Cold-heat and excess-deficiency pattern identification based on questionnaire, pulse, and tongue in cancer patients: a feasibility study, Journal of Korean Medicine 42(1):1-11, 2021 — https://doi.org/10.13048/jkm.21001
8. Ryu H, Lee H, Kim H, Kim J, Reliability and validity of a cold-heat pattern questionnaire for traditional Chinese medicine, Journal of Alternative and Complementary Medicine 16(6):663-667, 2010 — https://doi.org/10.1089/acm.2009.0331