Basic principles of pattern discrimination

The process of determining which actual pattern is on hand is called 辩证 (pinyin: biàn zhèng, usually translated as "pattern diagnosis",[117] "pattern identification"[118] or "pattern discrimination"[82]). Generally, the first and most important step in pattern diagnosis is an evaluation of the present signs and symptoms on the basis of the "Eight Principles" (八纲, pinyin: bā gāng).[118][119] These eight principles refer to four pairs of fundamental qualities of a disease: exterior/interior, heat/cold, vacuity/repletion, and yin/yang.[118] Out of these, heat/cold and vacuity/repletion have the biggest clinical importance.[118] The yin/yang quality, on the other side, has the smallest importance and is somewhat seen aside from the other three pairs, since it merely presents a general and vague conclusion regarding what other qualities are found.[118] In detail, the Eight Principles refer to the following:

Exterior (表, pinyin: biaǒ) refers to a disease manifesting in the superficial layers of the body - skin, hair, flesh, and meridians.[120] It is characterized by aversion to cold and/or wind, headache, muscle ache, mild fever, a "floating" pulse, and a normal tongue appearance.[120]
Interior (里, pinyin: lǐ)refers to disease manifestation in the zàng-fǔ, or (in a wider sense) to any disease that can not be counted as exterior.[121] There are no generalized characteristic symptoms of interior patterns, since they'll be determined by the affected zàng or fǔ entity.[122]
Cold (寒, pinyin: hàn) is generally characterized by aversion to cold, absence of thirst, and a white tongue fur.[123] More detailed characterization depends on whether cold is coupled with vacuity or repletion.[123]
Heat (热, pinyin: rè) is characterized by absence of aversion to cold, a red and painful throat, a dry tongue fur and a rapid and floating pulse, if it falls together with an exterior pattern.[124] In all other cases, symptoms depend on whether heat is coupled with vacuity or repletion.[125]
Vacuity (虚, pinyin: xū) often referred to as "deficiency", can be further differentiated into vacuity of qi, xuě, yin and yang, with all their respective characteristic symptoms.[126] Yin vacuity can also be termed "vacuity-heat", while yang vacuity is equivalent to "vacuity-cold".[127]
Repletion (实, pinyin: shí) often called "excess", generally refers to any disease that can't be identified as a vacuity pattern, and usually indicates the presence of one of the Six Excesses,[128] or a pattern of stagnation (of qi, xuě, etc.).[129] In a concurrent exterior pattern, repletion is characterized by the absence of sweating.[124] The signs and symptoms of repletion-cold patterns are equivalent to cold excess patterns, and repletion-heat is similar to heat excess patterns.[130]
Yin and yang are universal aspects all things can be classified under, this includes diseases in general as well as the Eight Principles' first three couples.[131] For example, cold is identified to be a yin aspect, while heat is attributed to yang.[131] Since descriptions of patterns in terms of yin and yang lack complexity and clinical practicality, though, patterns are usually not labelled this way anymore.[131] Exceptions are vacuity-cold and repletion-heat patterns, who are sometimes referred to as "yin patterns" and "yang patterns" respectively.[131]
After the fundamental nature of a disease in terms of the Eight Principles is determined, the investigation focuses on more specific aspects.[118] By evaluating the present signs and symptoms against the background of typical disharmony patterns of the various entities, evidence is collected whether or how specific entities are affected.[132] This evaluation can be done

in respect of the meridians (经络辩证, pinyin: jīng-luò biàn zhèng)[88]
in respect of qi (气血辩证, pinyin: qì xuě biàn zhèng)[82]
in respect of xuě (气血辩证, pinyin: qì xuě biàn zhèng)[82]
in respect of the body fluids (津液辩证, pinyin: jīn-yė biàn zhèng)[82]
in respect of the zàng-fǔ (脏腑辩证, pinyin: zàng-fǔ biàn zhèng)[82] - very similar to this, though less specific, is disharmony pattern description in terms of the Five Elements [五行辩证, pinyin: wǔ xíng biàn zhèng][133])
There are also three special pattern diagnosis systems used in case of febrile and infectious diseases only ("Six Channel system" or "six division pattern" [六经辩证, pinyin: liù jīng biàn zhèng]; "Wei Qi Ying Xue system" or "four division pattern" [卫气营血辩证, pinyin: weì qì yíng xuě biàn zhèng]; "San Jiao system" or "three burners pattern" [三角辩证, pinyin: sānjiaō biàn zhèng]).[86][134]