张介宾曰。合病者。乃二阳三阳同病。病之相合者也。并病者。如太阳先病不解。又并入阳明
少阳之类也。观仲景曰。二阳并病。太阳初得病时。发其汗。汗先出不彻。因转属阳明。若太阳症
不罢者。不可下。按此云转属阳明。则自太阳而来。可知也。云太阳症不罢。则二经皆病可知也。
凡并病者。由浅而深。由此而彼。势使之必然也。此合病并病之义。不知者因以为罕见之病。又岂
知今时之病。皆合病并病哉。余自临症以来。初未见有单经挨次相传者。亦未见有表症悉罢。止存
里症者。若欲根据经如式求症。则未见有如式之病。而方治可相符者。是皆不知合病并病之义耳。今
列其大略如下。合病者。乃二经三经同病也。如初起发热恶寒头痛。此太阳之症。而更兼不眠。即
太阳阳阴合病也。若兼呕恶。即太阳少阳合病也。若发热不眠呕恶。即阳明少阳合病也。若三者俱全。
便是三阳合病。而其病必甚。三阳与三阴本无合病。盖三阳为表。三阴为里。若表里同病。即两
感也。故凡阴阳俱病者。必以渐相并而至皆并
病耳。此亦势所必至。非合病两感之谓。合病与并病不同。合病者。彼此齐病也。并病者。一经先病。然后传及他经而
皆病也。如太阳
先病发热头痛。而后见目痛鼻干不眠等症。此太阳并于阳明也。或后见耳聋胁痛呕而口苦等症。此
太阳并于少阳也。或后见腹满嗌干等症。此太阳并于太阴也。或后见舌干口燥等症。此太阳并于少
阴也。或后见烦满囊缩等症。此太阳并于厥阴也。若阳明并于三阴者。必鼻干不眠而兼三阴之症。
少阳并于三阴者。必耳聋呕苦而兼三阴之症。阴症虽见于里。而阳症仍留于表。故谓之并。凡患伤
寒而终始热有不退者。皆表邪之未解耳。但得正汗一透。则表里皆愈。岂非阴阳相并之病乎。今之伤
寒。率多并病。若明此理。则自有头绪矣。治此之法。凡并病在三阳者。自当解三阳之表。如邪在
太阳者。当知为阳中之表。治宜轻清。邪在阳明者。当知为阳中之里。治宜浓重。邪在少阳者。
当知为阳中之枢。治宜和解。此皆治表之法也。至于病入三阴。本为在里。如太阴为阴中之阳。治
宜微温。少阴为阴中之枢。治宜半温。厥阴为阴中之阴。治宜大温。此阴症之治略也。然病虽在阴。
而有兼三阳之并病者。或其热邪已甚。自宜清火。或其表尚未解。仍当散邪。盖邪自外入。则外
为病本。拔去其本。则里病自无不愈者。此所以解表即能和中也。若表邪不甚。而里症为急。又当
先救其里。以表里之气本自相关。惟表不解。所以里病日增。惟里不和。所以表病不散。此所以治
里亦能解表也。但宜表宜里。自有缓急先后。一定不易之道。而非可以疑似出入者。要在乎知病之
薮。而独见其必胜之机耳。此又阴阳并病之治法也。惟是病既在阴。必关于脏。脏气为人之根本。
而死生系之。故凡诊阴症者。必当细察其虚实。而补泻寒热。弗至倒施。则今时之治要。莫切于此
矣。
张介宾说：合病，是指两阳经或三阳经同时发病，是病邪相互合并的情况。并病，例如太阳经先发病而未愈，病邪又传入阳明经或少阳经等情况。看张仲景说：“二阳并病，太阳经初得病时，用发汗法治疗，汗出得不透彻，因此病邪转属到阳明经。如果太阳经的症状没有消除，不可使用下法。”按照这里所说的“转属阳明”，可知病邪是从太阳经传来的；说“太阳经症状未消除”，则可知两经都在发病。
凡是并病，都是由浅入深，由此经传到彼经，这是病情发展的必然趋势。这就是合病和并病的含义。不了解的人因此认为这是罕见的疾病，又哪里知道当今时代的疾病，都是合病和并病呢？我自临症以来，从未见过有单条经脉依次相传的病例，也从未见过表证完全消失、只存留里证的病例。如果想要严格按照经典条文来求索病症，就看不到符合条文的病证，也没有能完全对应的方治。这都是因为不了解合病和并病的含义罢了。现在列出其大概情况如下：
合病，是指两经或三经同时发病。比如初起时发热、恶寒、头痛，这是太阳经的症状，但如果兼见不眠，就是太阳经与阳明经的合病。如果兼见呕吐恶心，就是太阳经与少阳经的合病。如果发热、不眠、呕吐恶心三者具备，就是阳明经与少阳经的合病。如果这三者全部具备，就是三阳合病，而且病情一定很重。三阳经与三阴经本来没有合病之说，因为三阳经主表，三阴经主里。如果表里同病，就是两感病。所以凡是阴阳两经都发病的，必然是逐渐相并而至，都属于并病范畴。这也是病情发展的必然结果，不是合病或两感的概念。
合病与并病不同。合病，是指两经同时发病；并病，是指一经先发病，然后传及他经而两经皆病。例如太阳经先发病，出现发热、头痛，随后出现目痛、鼻干、不眠等症状，这是太阳经并入阳明经。或者随后出现耳聋、胁痛、呕吐且口苦等症状，这是太阳经并入少阳经。或者随后出现腹部胀满、咽喉干燥等症状，这是太阳经并入太阴经。或者随后出现舌干、口燥等症状，这是太阳经并入少阴经。或者随后出现心烦腹满、阴囊收缩等症状，这是太阳经并入厥阴经。如果是阳明经并入三阴经，必定有鼻干、不眠并兼有三阴经的症状。如果是少阳经并入三阴经，必定有耳聋、呕吐口苦并兼有三阴经的症状。阴经的病虽然表现在里，但阳经的症状仍然留在表，所以称为并病。
凡是患伤寒病，始终发热不退的，都是表邪未解的缘故。只要得到真正的汗出透达，那么表里都会痊愈。这难道不是阴阳相并的病吗？现在的伤寒病，大多属于并病。如果明白这个道理，自然就有头绪了。治疗这种病的方法：凡是并病在三阳经的，自然应当解除三阳经的表邪。如邪气在太阳经，应当知道它是阳中之表，治疗宜用轻清之剂；邪气在阳明经，应当知道它是阳中之里，治疗宜用浓重之剂；邪气在少阳经，应当知道它是阳中之枢机，治疗宜用和解之法。这些都是治表的方法。
至于病邪进入三阴经，本是在里。如太阴经是阴中之阳，治疗宜用微温之法；少阴经是阴中之枢，治疗宜用半温之法；厥阴经是阴中之阴，治疗宜用大温之法。这是治疗阴经病症的大略原则。然而，病虽然在阴经，但有兼夹三阳经的并病情况，或者热邪已经很盛，自然应当清热泻火；或者表邪尚未解除，仍当发散邪气。因为邪气从外而入，外表就是病的根本，拔除这个根本，里面的病自然无不痊愈。这就是所谓“解表即能和中的道理”。如果表邪不严重，而里证为急迫，又应当先救里。因为表里之气本是相互关联的，正因为表邪不解，所以里病日益增加；正因为里气不和，所以表病不能消散。这就是所谓“治里亦能解表”的道理。但是，该解表还是该治里，自有缓急先后的定法，而不是可以模棱两可随意出入的。关键在于懂得疾病的根源，并能独自洞察必胜的契机罢了。这又是阴阳并病的治疗法则。
只是既然病在阴经，必然关系到脏腑。脏气是人的根本，生死系于此。所以凡是诊断阴经病症的，必须仔细辨别其虚实，使补泻寒热的运用不至于颠倒错施，这才是当今时代治疗的要点，没有比这更切要的。
Zhang Jiebin stated: Hebing (Concurrent Disease) refers to the simultaneous onset of pathologies in two or three Yang meridians, representing a merging of diseases. Bingbing (Sequential Disease) occurs when, for example, the Taiyang meridian is initially affected and the pathology remains unresolved, subsequently spreading to the Yangming or Shaoyang meridians. As Zhang Zhongjing noted: "In Bingbing of two Yang meridians, when the Taiyang disease is first contracted, diaphoresis is applied. If the sweating is incomplete, the pathology transfers to the Yangming." If the symptoms of the Taiyang meridian have not ceased, purgation should not be used. The phrase "transfers to Yangming" indicates the origin from Taiyang; stating that "Taiyang symptoms persist" confirms that both meridians are involved.
Generally, Bingbing progresses from superficial to deep, transmitting from one meridian to another, which is an inevitable trend of disease progression. This defines the meaning of Hebing and Bingbing. Those who do not understand this may consider it a rare condition, yet they fail to realize that contemporary diseases are predominantly Hebing and Bingbing. Since I began clinical practice, I have never encountered cases where transmission follows a single meridian sequentially, nor have I seen cases where exterior symptoms completely resolve leaving only interior symptoms. If one seeks symptoms strictly according to classical textual patterns, such precise presentations are rarely found, nor are there formulas that perfectly match them. This stems from a lack of understanding of Hebing and Bingbing. The following outlines the general principles:
Hebing refers to the simultaneous involvement of two or three meridians. For instance, initial fever, aversion to cold, and headache are symptoms of the Taiyang meridian; if accompanied by insomnia, it constitutes Hebing of the Taiyang and Yangming meridians. If accompanied by vomiting and nausea, it is Hebing of the Taiyang and Shaoyang meridians. If fever, insomnia, vomiting, and nausea all present, it is Hebing of the Yangming and Shaoyang meridians. If all three sets of symptoms are present, it is Hebing of the Three Yang meridians, indicating severe pathology. There is no concept of Hebing between the Three Yang and Three Yin meridians because the Three Yang govern the exterior and the Three Yin govern the interior. Simultaneous involvement of exterior and interior is termed Lianggan (Double Strike). Therefore, when both Yin and Yang meridians are affected, it inevitably progresses through gradual transmission, classifying it as Bingbing rather than Hebing or Lianggan.
The distinction lies in timing: Hebing implies simultaneous onset, whereas Bingbing implies sequential transmission from one meridian to others. For example, if Taiyang disease presents with fever and headache, followed later by eye pain, nasal dryness, and insomnia, this is Taiyang Bingbing into Yangming. If followed by deafness, hypochondriac pain, vomiting, and bitter taste, it is Taiyang Bingbing into Shaoyang. If followed by abdominal fullness and dry throat, it is Taiyang Bingbing into Taiyin. If followed by dry tongue and mouth, it is Taiyang Bingbing into Shaoyin. If followed by irritability, abdominal fullness, and retraction of the genitals, it is Taiyang Bingbing into Jueyin. If Yangming transmits to the Three Yin, nasal dryness and insomnia will coexist with Yin symptoms. If Shaoyang transmits to the Three Yin, deafness, vomiting, and bitter taste will coexist with Yin symptoms. Although Yin pathology manifests internally, Yang symptoms remain on the exterior, hence termed Bingbing.
In Shanghan (Cold Damage) cases where fever persists throughout, it indicates that exterior pathogens have not been resolved. Once proper sweating occurs, both exterior and interior conditions heal. Is this not a case of Yin-Yang Bingbing? Contemporary Shanghan cases are mostly Bingbing; understanding this principle provides clarity. Treatment for Bingbing involving the Three Yang meridians requires resolving the exterior of these meridians. Pathogens in Taiyang are considered the exterior of Yang; treatment should use light and clear methods. Pathogens in Yangming are the interior of Yang; treatment should use heavy and concentrated methods. Pathogens in Shaoyang are the pivot of Yang; treatment should employ harmonizing methods. These are exterior-resolving strategies.
For pathology entering the Three Yin meridians, which are interior: Taiyin is Yin within Yang; treatment uses mild warming. Shaoyin is the pivot of Yin; treatment uses semi-warming. Jueyin is Yin within Yin; treatment uses strong warming. These are general principles for treating Yin diseases. However, even when pathology is in the Yin meridians, concurrent Bingbing with the Three Yang may occur. If heat pathogens are intense, clearing fire is appropriate. If exterior pathogens remain unresolved, dispersing them is necessary. Since pathogens enter from outside, the exterior is the root; removing the root ensures internal recovery. Thus, resolving the exterior can harmonize the middle. Conversely, if exterior pathogens are mild but interior symptoms are urgent, one must prioritize rescuing the interior. Exterior and interior Qi are interrelated; unresolved exterior leads to worsening interior, and disharmonious interior prevents exterior resolution. Thus, treating the interior can also resolve the exterior. There is a fixed order of priority regarding whether to treat exterior or interior, avoiding ambiguity. One must grasp the essence of the disease and discern the decisive factor for victory. This constitutes the treatment method for Yin-Yang Bingbing.
Since Yin pathology involves the Zang organs, which are the foundation of life and determine survival, diagnosing Yin diseases requires careful differentiation of deficiency and excess to ensure tonification, purgation, warming, and cooling are applied correctly. This is the most critical aspect of contemporary treatment.