病有发热恶寒者。发于阳也。无热恶寒者。发于阴也。发于阳者七日愈。发于阴者六日愈。以阳数七。阴
数六也。
此一节。提挈纲领。统论阴阳。当冠于六经之首。自叔和无己诸家。错简于太阳脉证之后。致喻氏以未
热注无热。悖于立言之旨矣。盖仲景以外邪之感。受本难知。发则可辨。因发知受。有阴经阳经之不同。
故分发热无热之各异。以定阳奇阴偶之愈期也。发于阳者。邪入阳经而发也。发于阴者。邪入阴经而发也。即
阴阳应象论所谓阳胜则身热。阴胜则身寒。阴阳更胜之变也。发热恶寒者。如太阳居身之表。营卫之所
流行也。营卫者。即谷之一气所化也。卫行脉外。本下焦命门之真阳。蒸谷气而布皮肤。司开阖而固毛孔者也。
营行脉中。本上焦太阴之真气。降中焦谷气之精华。以滋养灌溉。充贯夫一身者也。若风伤卫。则卫阳受
邪。故头项强痛。发热恶风而汗出也。寒伤营。则营阴受邪。
故头项强痛。发热恶寒。无汗体痛呕逆也。营卫虽有浅深。其发于太阳则一也。若阳明之经。已在营
卫之内。肌肉腠理之中。虽无关营卫。亦必由营卫而入。故有一日得之。不发热而恶寒者。逮邪气既
入阳明。则恶寒自罢。身热汗自出。不恶寒而反恶热矣。然汗虽多尚微发热恶寒者。犹为外证未解也。
若入里则发潮热矣。故热不潮者。尚未可与承气汤也。少阳为躯壳之里层。自此以外。由阳明而达太阳。
故属阳分而为表。少阳犹是三阳之内面。故称半表。自此以内。则肠胃脏腑也。故为阴分而为里。少
阳乃胃肠脏腑之匡郭。故为半里。盖统系隶乎表。而部位接于里也。邪气犯之。非若太阳居表邪之所
客者浅近。恶寒即能发热。发热即能恶寒。寒热每多并作。唯少阳一经。邪之所入者深远。其出而达
于皮肤营卫不易。故其发也。则如疟而往来寒热矣。夫三阳发热。状虽不同。而发热则无不同也。至
于三阴本无发热之例。四逆恶寒。其常也。间有反发热。反不恶寒。手足反温。其变也。如太阴表证。并
无发热者。一则曰太阴中风。四肢烦疼。阳微阴涩而长者为欲愈。又曰太阴病。脉浮者可发汗。宜桂
枝汤。又曰伤寒脉浮而缓。手足自温者。系在太阴。皆太阴无热之表证也。至少阴病。则曰始得之反
发热矣。发热而曰反者。因无热者而又发热。故谓之反也。乃少阴虚寒之表证。故以麻黄附子细辛汤主之。
少阴证。得之二三日。口中和。其背恶寒者。当灸之而以附子汤主之。又如少阴病。恶寒身蜷而利。
手足逆冷者。少阴病。四逆恶寒而身蜷。脉不至。不烦而躁。是皆恶寒而无热之谓也。又若少阴病下
利清谷。里寒外热。手足厥逆。脉微欲绝。身反不恶寒。此又以不恶寒为反也。其外热面赤。亦非发
热之热。乃阴盛格阳于外也。至少阴病下利。若利自止。恶寒而蜷卧。手足温者可治。少阴病。脉紧。
至七八日自下利脉暴微。手足反温。脉紧反去者为欲解。少阴病。吐利。手足不逆冷。反发热者不死。
此又以手足温及发热为
反。皆发于阴而无热之谓也。谓之不死者。以阴邪渐退。阳气将回。温经复阳之治可施也。若在厥阴。
发热者极多。恶寒者甚少。而实阴阳相半。然仍以阳气为重。故热者必厥。厥者必热。而以厥少热多
为病之退。厥多热少为病之进也。至若发热下利厥躁者。非真发热也。乃阴盛阳绝。阴阳离隔。必死
之证也。夫发于阴者本无热。故凡有热者。不曰反发热。则曰反不恶寒。反之为言。不当得而得。当
然而不然也。凡此真寒假热之证。悉标举于三阴见证之中。岂非无热为三阴之根据乎。其所谓发于阴者。
舍三阴而何指乎。乃成氏旧注。谓阳为热。阴为寒。以发热恶寒为寒伤阳。无热恶寒为寒伤阴。固不
足以窥仲景之 篱。而喻氏仍方氏之旧。以风为阳。卫亦阳。故病起于阳。寒为阴。营亦阴。故病起
于阴。若论邪气止在太阳一经。其说犹可。若以此该贯六经。则有大谬不然者矣。况又以无热恶寒句。谓指
寒邪初受。未郁为热而言。少顷。郁勃于营间。则仍发热矣。若以未郁为热之少顷。即谓之无热。恐
仲景立言。未必若是其歧也。若必以风伤卫为发于阳。寒伤营为发于阴。则在三阳经之称伤寒者。皆
可谓之发于阴矣。然则三阴条中。亦有以中风冠之者。亦可谓之发于阳乎。以理烛之。岂其然乎。所
谓阳七日。阴六日者。概言其理所当然。而非必然者也。七者。阳之复。少阳之数也。六者。阴之极。
老阴之数也。盖阳数始于一而终于九。阴数起于二而极于六。此天地阴阳之至数也。然一极之中。分
阴分阳而为两仪。两仪各分太少而为四象。则阴阳各有太少矣。何独阳取其少而阴取其老乎。盖阳以
少为用。阴以老为极。阳少则为生气。阴极则为阳生。故皆为愈期。此阴阳消长之自然也。其所以阳
七日者。阳动而变。故能游行于经脉之表。七日经尽而邪衰。如素问热论所谓其不两感于寒者。七日
巨阳病衰。头痛少愈也。其所以阴六日者。阴静而守。不若阳经之循行周遍。至六日而阴极阳回。如
三阴证中之手足温。
热胜于厥而自愈也。其有不应期而愈者。则当察其失治误治。或邪盛。或正虚。或入里。或犯脏。及
过经等证。又不可以常理拘也。夫发热无热。辨证之源也。发阳发阴。知治之本也。阳奇阴偶。收效之
数也。岂非贯始终。括六经。标全论之宗旨乎。
余读仲景书而见其参同于易也。夫全易。一奇偶也。全论。一阴阳也。六子之生于乾坤。六经之
禀于阴阳也。六经之浅深正变。旁行叠见。形能百出。则卦爻之动变。象数之纷淆也。圣人以言不尽
意而图理于象。使人即象以穷理。仲景以法不尽证而以寒热分阴阳。使人辨证以尽法。故首标易知之
寒热。易辨之阴阳。然后申其证变。出其方法。而后可以言治也。夫证即象也。法即理也。三百九十七法。
不出六经之中。六经不出乎阴阳之外。能读仲景书者。其唯深于易者乎。
疾病有出现发热并伴有恶寒症状的，这是病发于阳经。没有发热而仅有恶寒症状的，这是病发于阴经。病发于阳经的，经过七天可以痊愈；病发于阴经的，经过六天可以痊愈。这是因为阳数的成数是七，阴数的成数是六。
这一段文字提纲挈领，总论阴阳，应当置于六经论述之首。自从王叔和以及后世诸家以来，将此段错简（错误地编排）在太阳脉证之后，导致喻嘉言将“未热”注解为“无热”，违背了张仲景立论的本意。大概是因为张仲景认为外邪侵袭人体，受邪之初难以知晓，但发病后则可以辨别，通过发病的表现来推断受邪的情况，由于有阴经和阳经的不同，所以表现出发热和无热的差异，从而确定了阳奇数、阴偶数的痊愈日期。所谓发于阳，是指邪气侵入阳经而发病；所谓发于阴，是指邪气侵入阴经而发病。这正是《黄帝内经·阴阳应象大论》中所说的“阳胜则身热，阴胜则身寒”，是阴阳偏胜变化的体现。
发热且恶寒的情况，如太阳病居于体表，是营气和卫气流行的部位。营气和卫气，是由水谷精气所化生的。卫气行于脉管之外，本源在于下焦命门的真阳，它蒸腾谷气布散于皮肤，主管毛孔的开阖以固护肌表。营气行于脉管之中，本源在于上焦太阴的真气，它下降中焦水谷精气的精华，用以滋养灌溉，充盈贯通全身。如果风邪伤害卫气，则卫阳受邪，所以出现头项强痛、发热、恶风且汗出。如果寒邪伤害营气，则营阴受邪，所以出现头项强痛、发热、恶寒、无汗且身体疼痛、呕吐逆气。营卫之气虽然有深浅之分，但它们发于太阳经则是相同的。至于阳明经，已经在营卫之内的肌肉腠理之中，虽然不直接关乎营卫的表层病变，但也必然由营卫而入。所以有的第一天患病时，不发热而恶寒，等到邪气进入阳明经后，恶寒自然停止，身体发热且自汗出，不再恶寒反而恶热。然而，如果出汗虽多但仍轻微发热恶寒的，说明表证尚未解除。如果邪气入里，则会发潮热。所以如果不发潮热，就还不能使用承气汤。少阳经位于躯壳的里层，由此向外，经由阳明到达太阳，所以属于阳分而为表；少阳犹在三阳经的内面，所以称为半表；由此向内，则是肠胃脏腑，所以属于阴分而为里。少阳乃是胃肠脏腑的外围屏障，所以称为半里。可以说，少阳统系隶属于表，而部位连接于里。邪气侵犯少阳，不像太阳居表那样邪客浅近，（太阳病）恶寒就能发热，发热就能恶寒，寒热往往同时发作。唯独少阳一经，邪气侵入较深，想要外出达到皮肤营卫并不容易，所以它的发病，就像疟疾一样往来寒热。三阳经的发热，症状虽然不同，但都有发热这一特点。至于三阴经，本来没有发热的先例，四肢厥冷且恶寒是其常态。间或有反常发热、反常不恶寒、手足反常温暖的情况，这是变证。例如太阴病的表证，并没有发热，一则说太阴中风，四肢烦疼，脉象阳微阴涩而长的是将要痊愈；又说太阴病，脉浮的可以发汗，适宜用桂枝汤；又说伤寒脉浮而缓，手足自温的，病系在太阴，这些都是太阴无热的表证。到了少阴病，则说初得病时反常发热。发热之所以叫“反”，是因为本应无热却又发热，所以称为反。这是少阴虚寒的表证，所以用麻黄附子细辛汤主治。少阴证，得病二三天，口中平和不燥，背部恶寒的，应当施灸并用附子汤主治。又如少阴病，恶寒、身体蜷缩且下利，手足逆冷的；少阴病，四肢厥冷、恶寒且身体蜷缩，脉搏摸不到，不烦躁却躁动不安，这些都是恶寒而无热的表现。又如少阴病下利清谷（完谷不化），里有寒而外有热，手足厥冷，脉搏微弱几乎要断绝，身体反常不恶寒，这里又以“不恶寒”为反常。其外表的热象和面色发红，也不是真正的发热，而是阴盛格阳于外所致。到少阴病下利，如果下利自行停止，恶寒且蜷卧，但手足温暖的，是可以治疗的。少阴病，脉紧，到了七八日自行下利，脉搏突然变得微弱，手足反常温暖，脉紧反常消失的，是快要解除了。少阴病，吐利，手足不逆冷，反常发热的，不会死亡，这里又以手足温暖和发热为反常，这都是病发于阴而无热的表现。称之为不死，是因为阴邪逐渐消退，阳气即将回复，此时可以施行温经复阳的治疗。如果在厥阴经，发热的情况极多，恶寒的情况很少，但实际上阴阳各占一半。然而仍以阳气为重，所以热的时候必定伴随厥冷，厥冷的时候必定伴随发热，而以厥少热多为病退，厥多热少为病进。至于出现发热、下利、厥逆且躁动的，不是真正的发热，而是阴盛阳绝，阴阳离决，是必死的证候。
病发于阴者，本来没有热，所以凡是有热的，要么叫“反发热”，要么叫“反不恶寒”。“反”的意思，是不当得而得，当然而不然。凡是这种真寒假热的证候，都列举在三阴见证之中，这难道不是以无热作为三阴病的基础吗？所谓发于阴，除了三阴经还能指什么呢？然而成无己的旧注，认为阳就是热，阴就是寒，把发热恶寒解释为寒伤阳，无热恶寒解释为寒伤阴，这根本不足以窥探张仲景学术的藩篱。而喻嘉言仍然沿袭方有执的旧说，认为风为阳，卫亦属阳，所以病起于阳；寒为阴，营亦属阴，所以病起于阴。如果只讨论邪气仅在太阳一经的情况，这种说法还可以接受；但如果以此概括六经，那就有大谬误了。况且他又将“无热恶寒”一句，解释为指寒邪刚受，尚未郁结化为热的情况，过了一会儿，郁勃于营分之间，就会再次发热。如果把尚未郁结为热的那一小会儿，就叫做无热，恐怕张仲景立论未必如此歧义。如果一定要把风伤卫称为发于阳，寒伤营称为发于阴，那么在三阳经中被称为伤寒的，都可以称为发于阴了。然而在三阴条文中，也有以中风开头的，难道也可以称为发于阳吗？用道理来审视，难道会是这样吗？所谓阳七日愈、阴六日愈，概而言之是理所当然，而非必然如此。七，是阳的复数，也是少阳的生数；六，是阴的极数，也是老阴的成数。大概阳数始于一而终于九，阴数起于二而极于六，这是天地阴阳的至数。然而在极数之中，分阴分阳而为两仪，两仪各自分为太少而为四象，那么阴阳各有太少之分了，为什么唯独阳取少阳之数而阴取老阴之数呢？大概阳以少为用，阴以老为极。阳少则为生气，阴极则为阳生，所以都作为痊愈的日期，这是阴阳消长的自然规律。之所以阳七日愈，是因为阳主动而善变，所以能游行于经脉之表，七日经气尽而邪气衰退，正如《素问·热论》所说，那些没有两感于寒的，第七天巨阳病衰，头痛稍微减轻。之所以阴六日愈，是因为阴主静而守位，不像阳经那样循行周遍，到了第六天阴极阳回，如三阴证中的手足转温，热胜于厥而自愈。如果有不按期痊愈的，则应当考察是否失治误治，或是邪气盛，或是正气虚，或是邪气入里，或是侵犯脏腑，以及过经传变等证候，又不可以用常规的道理来拘泥了。发热与无热，是辨证的源头；发于阳与发于阴，是知治的根本；阳奇阴偶，是收效的定数。这难道不是贯穿始终、括括六经、标示全篇宗旨的吗？
我读张仲景的书，发现其中与《易经》相通。整个《易经》，不过是奇数和偶数；整个《伤寒论》，不过是阴阳二字。八卦中的六子生于乾坤，六经禀受于阴阳。六经的浅深正变，旁行叠见，形态变化百出，就像卦爻的变动和象数的纷乱复杂。圣人因为言语不能完全表达心意，所以画图理于象中，使人通过象来穷究理。张仲景因为方法不能完全涵盖所有证候，所以用寒热来区分阴阳，使人通过辨证来穷尽方法。所以首先标举容易知晓的寒热，容易辨别的阴阳，然后阐述其证候变化，提出治疗方法，然后才可以谈论治疗。证候就是象，方法就是理。三百九十七种治法，不出六经的范围；六经，也不出阴阳的范围。能读懂张仲景书的，大概只有深通《易经》的人吧。
Diseases that present with fever and aversion to cold originate in the Yang aspect. Those without fever but with aversion to cold originate in the Yin aspect. Diseases originating in the Yang aspect typically resolve after seven days, while those originating in the Yin aspect typically resolve after six days. This is because seven is the number associated with Yang completion, and six is the number associated with Yin completion.
This section serves as a general outline summarizing Yin and Yang, and should ideally be placed at the beginning of the discussion on the Six Channels (Liu Jing). Since Wang Shuhe and subsequent scholars erroneously misplaced this text after the pulse and symptom patterns of the Taiyang channel, Yu Jia Yan interpreted "no fever" as "not yet having fever," which contradicts Zhang Zhongjing's original intent. Generally, when external pathogenic factors invade the body, the initial state of invasion is difficult to discern, but once symptoms manifest, they can be identified. By observing the manifestation, one can infer the nature of the invasion. Due to differences between Yin and Yang channels, manifestations differ in the presence or absence of fever, thereby determining the healing periods based on odd numbers for Yang and even numbers for Yin. "Originating in Yang" refers to pathogens entering Yang channels; "originating in Yin" refers to pathogens entering Yin channels. This aligns with the *Huangdi Neijing* (Yellow Emperor's Inner Canon) stating, "Yang excess leads to body heat, Yin excess leads to body cold," representing variations in Yin-Yang imbalance.
Fever accompanied by aversion to cold occurs in Taiyang disease, which resides on the exterior of the body where Ying (Nutrient) Qi and Wei (Defensive) Qi circulate. Ying and Wei Qi are transformed from the essence of food and drink. Wei Qi moves outside the vessels, originating from the True Yang of the Mingmen (Gate of Life) in the Lower Jiao. It steams the grain qi and distributes it to the skin, controlling the opening and closing of pores to secure the exterior. Ying Qi moves inside the vessels, originating from the True Qi of the Taiyin in the Upper Jiao. It descends the refined essence of middle Jiao grain qi to nourish, irrigate, and fill the entire body. If wind pathogen injures Wei Qi, then Wei Yang is affected, resulting in stiffness and pain in the head and neck, fever, aversion to wind, and sweating. If cold pathogen injures Ying Qi, then Ying Yin is affected, resulting in stiffness and pain in the head and neck, fever, aversion to cold, absence of sweat, body ache, vomiting, and regurgitation. Although Ying and Wei have depths of penetration, their manifestation in the Taiyang channel is consistent. Regarding the Yangming channel, it lies within the Ying and Wei, in the muscles and interstices. Although not directly concerning the superficial Ying and Wei, pathogens must still enter through them. Thus, some may experience no fever but only aversion to cold on the first day. Once the pathogen enters Yangming, aversion to cold ceases, body heat appears, spontaneous sweating occurs, and there is aversion to heat rather than cold. However, if there is profuse sweating yet slight fever and aversion to cold persist, the exterior syndrome has not yet resolved. If the pathogen enters the interior, tidal fever will develop. Therefore, if there is no tidal fever, Chengqi Tang (Cathartic Decoction) should not yet be used. Shaoyang (Lesser Yang) is the inner layer of the shell. From here outward, reaching Taiyang via Yangming, it belongs to the Yang aspect and is considered Exterior. Shaoyang is still the inner surface of the Three Yang channels, hence called Half-Exterior. From here inward lie the intestines, stomach, and zang-fu organs, belonging to the Yin aspect and considered Interior. Shaoyang acts as the framework surrounding the gastrointestinal organs, hence called Half-Interior. Its system attaches to the Exterior, while its location connects to the Interior. Pathogens attacking Shaoyang do not reside as superficially as in Taiyang. In Taiyang, aversion to cold can lead to fever, and fever can lead to aversion to cold; cold and heat often occur together. Only in Shaoyang does the pathogen penetrate deeply, making it difficult to exit to the skin and Ying/Wei. Thus, its manifestation resembles malaria, with alternating chills and fever. While the three Yang channels all feature fever, their presentations vary, yet fever is common to all. In contrast, the Three Yin channels generally do not present with fever; cold limbs and aversion to cold are the norm. Occasionally, there are atypical cases of fever, lack of aversion to cold, and warm hands and feet, which represent variations. For example, in Taiyang exterior syndromes, there is no fever. One text states that in Taiyin wind-stroke, with vexing pain in the four limbs, if the pulse is faint at the Cun position, choppy at the Chi position, but long, recovery is imminent. Another states that in Taiyin disease, if the pulse is floating, sweating methods may be used, preferably Guizhi Tang (Cinnamon Twig Decoction). Another states that in cold damage, if the pulse is floating and slow with spontaneously warm hands and feet, the disease relates to Taiyin. These are all Taiyin exterior syndromes without heat. Regarding Shaoyin disease, it is stated that initially there is atypical fever. The term "atypical" (fan) is used because fever appears when none is expected. This is an exterior syndrome of Shaoyin deficiency-cold, treated with Mahuang Fuzi Xixin Tang (Ephedra, Aconite, and Asarum Decoction). In Shaoyin syndrome, two or three days after onset, if the mouth feels normal and there is aversion to cold on the back, moxibustion should be applied, and Fuzi Tang (Aconite Decoction) administered. Similarly, in Shaoyin disease, with aversion to cold, curled-up posture, and diarrhea, or cold limbs; or in Shaoyin disease with cold limbs, aversion to cold, curled-up posture, absent pulse, restlessness without irritability—these are all aversion to cold without fever. Also, in Shaoyin disease with clear undigested stool in diarrhea, internal cold with external heat, cold limbs, and faint-to-absent pulse, if the body is atypically free of aversion to cold, this "lack of aversion" is atypical. The external heat and flushed face are not true fever but result from Yin excess repelling Yang to the exterior. In Shaoyin disease with diarrhea, if the diarrhea stops spontaneously, and although there is aversion to cold and a curled-up posture, the hands and feet are warm, treatment is possible. In Shaoyin disease, if the pulse is tight, and after seven or eight days spontaneous diarrhea occurs with the pulse suddenly becoming faint, hands and feet become warm, and the tightness disappears, resolution is near. In Shaoyin disease with vomiting and diarrhea, if hands and feet are not cold and there is atypical fever, death is not inevitable. Here, warm hands/feet and fever are termed "atypical." All these describe diseases originating in Yin without true heat. They are called non-fatal because Yin pathogens are receding and Yang Qi is returning, allowing for warming meridians and restoring Yang therapies. In Jueyin disease, fever is very common, while aversion to cold is rare, reflecting a balance of Yin and Yang, though Yang is prioritized. Thus, when there is heat, there is always cold limbs (Jue), and when there are cold limbs, there is heat. Fewer cold limbs and more heat indicate disease regression; more cold limbs and less heat indicate disease progression. However, fever with diarrhea, cold limbs, and restlessness is not true fever but indicates Yin excess and Yang exhaustion, separation of Yin and Yang, and is a fatal sign.
Since diseases originating in Yin inherently lack heat, any presence of heat is described as "atypical fever" or "atypical lack of aversion to cold." "Atypical" means something occurring that shouldn't, or failing to occur that should. All such true-cold/false-heat syndromes are listed among the Three Yin manifestations, underscoring that lack of heat is the basis of Three Yin diseases. When referring to "originating in Yin," what else could it refer to but the Three Yin channels? However, Cheng Wuji's old commentary claimed Yang equals heat and Yin equals cold, interpreting fever with aversion to cold as cold injuring Yang, and no fever with aversion to cold as cold injuring Yin. This fails to grasp Zhang Zhongjing's principles. Yu Jiayan followed Fang Youzhi, arguing wind is Yang, Wei is Yang, so disease starts in Yang; cold is Yin, Ying is Yin, so disease starts in Yin. This argument holds only if discussing pathogens confined to the Taiyang channel. Applying it to all Six Channels is a major error. Furthermore, interpreting "no fever with aversion to cold" as the initial stage before cold transforms into heat due to stagnation in Ying is flawed. If the brief period before transformation is called "no fever," Zhang Zhongjing's wording would be too ambiguous. If wind injuring Wei is "originating in Yang" and cold injuring Ying is "originating in Yin," then all "cold damage" in the Three Yang channels could be called "originating in Yin." Yet, some Three Yin sections begin with wind-stroke, which would imply "originating in Yang." Logically, this is inconsistent. The statement "Yang heals in seven days, Yin in six" describes a general principle, not an absolute rule. Seven is the number of Yang resurgence and Shaoyang generation; six is the number of Yin extremity and Old Yin completion. Yang numbers start at one and end at nine; Yin numbers start at two and peak at six, representing the ultimate numbers of Heaven and Earth. Within these extremes, Yin and Yang divide into Two Modes, which further divide into Four Images, meaning both Yin and Yang have "Less" and "More" aspects. Why choose Shaoyang (Less Yang) for Yang and Old Yin for Yin? Because Yang functions through "Less," while Yin reaches its extreme in "Old." Yang in its "Less" state generates life; Yin at its extreme gives birth to Yang. Thus, both serve as healing periods, reflecting the natural waxing and waning of Yin and Yang. Yang heals in seven days because Yang is active and changing, circulating on the exterior of meridians. After seven days, meridian qi exhausts the pathogen, as stated in *Suwen: Re Lun*: "For those not suffering from dual-channel cold attack, on the seventh day, Juyang (Taiyang) pathology declines, and headache improves." Yin heals in six days because Yin is static and stationary, unlike Yang channels that circulate fully. On the sixth day, Yin extremity allows Yang to return, as seen in Three Yin syndromes where warm hands/feet and heat overcoming cold lead to self-healing. Cases not healing on schedule require investigation into mismanagement, excessive pathogen, deficient healthy Qi, interior entry, organ involvement, or passing through channels, which cannot be bound by standard rules. Fever versus no fever is the source of differentiation; originating in Yang versus Yin is the foundation of treatment; odd/even numbers are the metrics of efficacy. Do these not encompass the beginning and end, summarize the Six Channels, and mark the core tenets of the entire treatise?
Reading Zhang Zhongjing's work reveals its correspondence with the *I Ching* (Book of Changes). The entire *I Ching* consists of odd and even lines; the entire *Shanghan Lun* consists of Yin and Yang. The six trigrams born from Qian and Kun correspond to the Six Channels derived from Yin and Yang. The depth, correctness, and variations of the Six Channels, appearing in complex layers and myriad forms, mirror the dynamic changes and numerical complexities of hexagrams and lines. The Sages, knowing words cannot fully express meaning, depicted principles through images, enabling people to explore principles via images. Zhang Zhongjing, knowing methods cannot cover all syndromes, divided Yin and Yang using cold and heat, enabling people to exhaust methods through differentiation. Thus, he first highlighted easily known cold/heat and easily distinguishable Yin/Yang, then elaborated on syndrome variations and methods, allowing for proper treatment. Syndromes are images; methods are principles. The 397 methods fall within the Six Channels; the Six Channels fall outside Yin and Yang. Only those deeply versed in the *I Ching* can truly understand Zhang Zhongjing's writings.