观《内经·至真要大论》所列病机。凡言火者五，言热者四，似皆谓之火也。然诸病之
见于诸篇者，复有此言热而彼言寒，此言实而彼言虚者，岂果本经之自为矛盾耶？盖诸篇所
言，在专悉病情，故必详必尽；在本篇所言，亦不过总言五运六气之大约，原非确指为实火
实热也。故于篇末，复以有无虚实四字总结于后，此轩岐之明见万世，正恐后人误以火热二
字，悉认为真因，而晓示如此。此其火有虚实，热有真假，从可知矣。余以刘河间《原病式
》之谬，故于《类经》惟引《经》释《经》，不敢杜撰一言，冀在解人之惑，以救将来之误
耳。前三卷中，别有详辨，并《类经》详注，俱当互阅求正。
凡虚火证，即假热证也。余于首卷寒热真假篇，已言之详矣。然犹有未尽者，如虚火之
病源有二，虚火之外证有四，何也？盖一曰阴虚者能发热，此以真阴亏损，水不制火也；
二曰阳虚者亦能发热，此以元阳败竭，火不归源也。此病源之二也。至若外证之四，则一曰
阳戴于上，而见于头面咽喉之间者，此其上虽热而下则寒，所谓无根之火也；二曰阳浮于外
，而发于皮肤肌肉之间者，此其外虽热而内则寒，所谓格阳之火也；三曰阳陷于下，而见于
便溺二阴之间者，此其下虽热而中则寒，所谓失位之火也；四曰阳亢乘阴，而见于精血髓液
之间者，此其金水败而铅汞干，所谓阴虚之火也，此外证之四也。然证虽有四，而本惟二，
或在阴虚，或在阳虚，而尽之矣。第阴虚之火唯一，曰金水败者，是也。阳虚之火有三，曰
上中下者，是也。凡治此者，若以阴虚火盛，则治当壮水。壮水之法，只宜甘凉，不宜辛热
。若以阳虚发热，则治宜益火。益火之法，只宜温热，大忌清凉。第温热之效速，每于一二
剂间，便可奏功。甘凉之力缓，非多服不能见效也。然清凉之药，终不宜多，多则必损脾胃
。如不得已，则易以甘平，其庶几耳。倘甘平未效，则惟有甘温一法，斯堪实济，尚可望其
成功。否则，生气之机，终非清凉所能致也。此义最微，不可不察。
一、气本属阳，阳气不足，则寒从中生。寒从中生，则阳无所存而浮散于外，是即虚火
假热之谓也。而假寒之证，其义亦然。是以虚火实火，亦总由中气之有虚实耳。凡气实于内
而为寒者，有如严冬阳伏于下，而阴凝于上，故冰雪满地而井泉温暖也。气虚于内而为热者
，有如盛夏阴盛于中，而阳浮于外，故炎暑逼人而渊源清冷也。天地间理原如此，故不可见
热即云热，见寒即云寒，而务察其寒热之本。
一、火有虚实，故热有假真，而察之之法，总当以中气为之主，而外证无足凭也。故凡
假热之证，本中寒也；假寒之证，本内热也。中寒者，原是阴证；内热者，原是阳证。第以
惑者不明，故妄以寒证为假热，热证为假寒。而不知内热者当远热，内寒者当远寒。内有可
据，本皆真病，又何假之有？
观察《黄帝内经·至真要大论》中列出的病机十九条。凡是提到“火”的有五条，提到“热”的有四条，似乎都指的是火证。然而，在其他篇章中提到的疾病，有的这里说热而那里说寒，这里说实证而那里说虚证，这难道是原典本身自相矛盾吗？大概各篇所述，是为了详尽地分析病情，所以必须详细完备；而在本篇中所述，也不过是概括五运六气的大致规律，原本并不是确切指实火和实热。所以在篇末，又用“有无虚实”四个字进行总结，这是黄帝与岐伯洞察万世的明智之举，正是担心后人误将“火热”二字全部当作真实病因，从而给予如此明示。由此可知，火分虚实，热有真假。我因为刘完素（河间）《原病式》中的谬误，所以在《类经》中只引用《内经》原文来解释《内经》，不敢凭空杜撰一言，希望解开读者的疑惑，以挽救后世的错误。前三卷中有其他详细的辨析，以及《类经》的详细注释，都应当互相参考以求得正确理解。
凡是虚火证，就是假热证。我在首卷《寒热真假篇》中已经讲得很详细了。然而还有未尽之处，比如虚火的病源有两个方面，虚火的外在表现有四种，为什么呢？大概一是阴虚者能够发热，这是因为真阴亏损，水不能制约火；二是阳虚者也能发热，这是因为元阳败竭，火不能回归本源。这就是病源的两个方面。至于外在表现的四种，则一是阳气戴于上部，表现在头面咽喉之间，这是上面虽然热而下面则寒，所谓的无根之火；二是阳气浮越于外部，表现在皮肤肌肉之间，这是外面虽然热而内部则寒，所谓的格阳之火；三是阳气陷于下部，表现在大小便及二阴之间，这是下面虽然热而中间则寒，所谓的失位之火；四是阳气亢盛乘袭阴分，表现在精血髓液之间，这是金水败坏而铅汞干枯，所谓的阴虚之火，这就是外在表现的四个方面。然而症状虽然有四种，但根本只有两种，或者在于阴虚，或者在于阳虚，这就涵盖了全部情况。其中阴虚的火只有一种，即所谓金水败坏的情况。阳虚的火有三种，即上、中、下三种情况。凡是治疗这种情况，如果是因为阴虚火盛，那么治疗应当壮水。壮水的方法，只宜用甘凉之品，不宜用辛热之药。如果是因阳虚发热，那么治疗宜益火。益火的方法，只宜用温热之品，大忌清凉之药。只是温热的效果迅速，往往在一两剂之间就能见效。甘凉的力量缓慢，不是多服不能见效。然而清凉的药物，终究不宜多用，多用必然损伤脾胃。如果不得已，则改用甘平之药，那还差不多。倘若甘平无效，则唯有甘温一法，才足以切实救助，尚有望成功。否则，生发之气，终究不是清凉所能达到的。这个道理最为微妙，不可不仔细考察。
其一，气本属于阳，阳气不足，则寒气从内生。寒气从内生，则阳气无处存留而浮散于外，这就是所说的虚火假热。而假寒证，其道理也是如此。因此，虚火和实火，总归是由中气的虚实决定的。凡是气实于内而导致寒的，就像严冬时阳气潜伏在下，阴气凝结在上，所以冰雪满地而井泉温暖。凡是气虚于内而导致热的，就像盛夏时阴气盛于中，阳气浮越于外，所以炎热逼人而水源清冷。天地间的道理原本就是这样，所以不可一见热就说是热，一见寒就说是寒，务必考察寒热的根本。
其二，火有虚实，所以热有假真，而察辨的方法，总应当以中气为主，而外在症状不足以凭信。所以凡是假热证，本质是中寒；假寒证，本质是内热。中寒者，原本是阴证；内热者，原本是阳证。只是因为迷惑的人不明理，所以妄地将寒证当作假热，热证当作假寒。却不知道内热者应当远离热邪，内寒者应当远离寒邪。体内有确凿依据，本质上都是真病，又有什么假的呢？
Observing the pathogenesis listed in *Huangdi Neijing: Zhi Zhen Yao Da Lun* (Treatise on the Most Essential and Important Aspects of Pathogenesis). There are five instances mentioning "fire" and four mentioning "heat," which seem to all refer to fire syndromes. However, in other chapters discussing diseases, some mention heat here and cold there, excess here and deficiency there. Could it be that the original classic is self-contradictory? The reason is that the descriptions in various chapters aim to exhaustively analyze the condition, thus requiring detailed completeness; whereas the description in this chapter merely summarizes the general principles of the Five Movements and Six Qi, originally not specifically referring to Excess Fire or Excess Heat. Therefore, at the end of the chapter, the four characters "Existence/Absence, Excess/Deficiency" are used to summarize. This demonstrates the profound insight of Huangdi and Qibo for all generations, precisely fearing that later generations might mistakenly regard the terms "Fire" and "Heat" as true causes, hence providing such clarification. From this, it can be known that Fire has Excess and Deficiency, and Heat has False and True natures. Due to the errors in Liu Hejian's *Yuan Bing Shi* (Original Treatise on Disease Causes), I only quoted the *Classic* to explain the *Classic* in *Lei Jing* (Classified Classic), daring not to fabricate a single word, hoping to resolve readers' doubts and prevent future errors. Detailed discussions in the first three volumes and annotations in *Lei Jing* should be consulted mutually for accuracy.
Any Xu Huo (Deficiency Fire) syndrome is essentially a Jia Re (False Heat) syndrome. I have discussed this in detail in the first volume under the chapter "True and False Cold and Heat." However, there are still incomplete aspects. For instance, why does Xu Huo have two sources of pathology and four external manifestations? First, individuals with Yin Deficiency can experience fever; this is due to the depletion of True Yin, where Water fails to control Fire. Second, individuals with Yang Deficiency can also experience fever; this is due to the exhaustion of Yuan Yang (Primordial Yang), where Fire fails to return to its source. These constitute the two pathological sources. Regarding the four external manifestations: First, Yang floats upward, appearing between the head, face, and throat; although the upper part feels hot, the lower part is cold. This is called "Rootless Fire." Second, Yang floats outward, appearing between the skin and muscles; although the exterior feels hot, the interior is cold. This is called "Ge Yang Fire" (Repelling Yang Fire). Third, Yang sinks downward, appearing between the urine/feces and the genital/anus region; although the lower part feels hot, the middle part is cold. This is called "Displaced Fire." Fourth, Yang hyperactivity attacks Yin, appearing between essence, blood, marrow, and fluids; this indicates the failure of Metal and Water, and the drying up of Lead and Mercury (metaphors for Kidney Essence and Lung Qi), referred to as "Yin Deficiency Fire." These constitute the four external manifestations. Although the symptoms are four, the root is only two: either Yin Deficiency or Yang Deficiency. Among these, the Fire of Yin Deficiency is unique, corresponding to the failure of Metal and Water. The Fire of Yang Deficiency has three types, corresponding to the Upper, Middle, and Lower regions. In treating these cases, if caused by Yin Deficiency with Fire Hyperactivity, treatment should involve "Strengthening Water." The method of Strengthening Water suits only Sweet-Cool herbs, avoiding Pungent-Warm ones. If caused by Yang Deficiency leading to fever, treatment should involve "Benefiting Fire." The method of Benefiting Fire suits only Warm-Hot herbs, strictly avoiding Cool-Cold ones. Warm-Hot methods act quickly, often achieving results within one or two doses. Sweet-Cool methods act slowly, requiring prolonged administration to show effects. However, Cool-Cold drugs should never be used excessively, as they will damage the Spleen and Stomach. If unavoidable, switching to Sweet-Ping (Neutral) herbs is preferable. If Sweet-Ping proves ineffective, only the Sweet-Warm method remains viable for substantial benefit, offering hope for success. Otherwise, the mechanism of generating vital energy cannot be achieved by Cool-Cold agents. This principle is subtle and must be carefully examined.
First, Qi inherently belongs to Yang. When Yang Qi is insufficient, Cold generates from within. When Cold generates from within, Yang has no place to reside and floats/scatters outward; this is what is meant by Xu Huo (Deficiency Fire) and Jia Re (False Heat). The logic for Jia Han (False Cold) is identical. Therefore, both Xu Huo and Shi Huo (Excess Fire) ultimately depend on the Excess or Deficiency of Zhong Qi (Middle Qi). When Qi is Excess internally causing Cold, it resembles deep winter where Yang hides below and Yin condenses above, resulting in snow and ice everywhere while wells remain warm. When Qi is Deficient internally causing Heat, it resembles midsummer where Yin is abundant in the center and Yang floats outward, resulting in oppressive heat while water sources remain cold. This is the natural order of heaven and earth. Thus, one must not simply label something Hot upon seeing heat, or Cold upon seeing cold, but must diligently investigate the root of Cold and Heat.
Second, since Fire has Excess and Deficiency, Heat has False and True aspects. The method of differentiation must primarily focus on Zhong Qi (Middle Qi), as external symptoms are unreliable. Therefore, any Jia Re (False Heat) syndrome originates from Zhong Han (Middle Cold); any Jia Han (False Cold) syndrome originates from Nei Re (Internal Heat). Zhong Han is fundamentally a Yin Syndrome; Nei Re is fundamentally a Yang Syndrome. Confused practitioners, lacking clarity, mistakenly treat Yin/Cold syndromes as False Heat and Yang/Heat syndromes as False Cold. They fail to realize that Internal Heat requires avoiding Heat, and Internal Cold requires avoiding Cold. Since the internal condition provides reliable evidence, these are essentially true diseases; what could possibly be false?