清者，清其热也。脏腑有热，则清之。经云∶热者寒之，是已。然有当清不清误人者，
有不当清而清误人者，有当清而清之不分内伤、外感以误人者，有当清而清之不量其人、不
量其证以误人者，是不可不察也。
夫六淫之邪，除中寒、寒湿外，皆不免于病热。热气熏蒸，或见于口舌、唇齿之间，或
见于口渴、便溺之际，灼知其热而不清，则斑黄狂乱，厥逆吐衄，诸症丛生，不一而足。此
当清不清之误也。
然又有不当清而清者何也？有如劳力辛苦之人，中气大虚，发热倦怠，心烦溺赤，名曰
虚火，盖春生之令不行，无阳以护其荣卫，与外感热证，相隔霄壤。又有阴虚劳瘵之证，日
晡潮热，与夫产后血虚，发热烦躁，证象白虎，误服白虎者难救。更有命门火衰，浮阳上泛
有似于火者。又有阴盛隔阳，假热之证，其人面赤狂躁，欲坐卧泥水中，或数日不大便，
或舌黑而润，或脉反洪大，峥峥然鼓击于指下，按之豁然而空者，或口渴欲得冷冻饮料而不能下
或因下元虚冷，频饮热汤以自救，世俗不识，误投凉药，下咽即危矣。此不当清而清之误
也。
然又有清之而不分内伤、外感者何也？盖风寒闭火，则散而清之，经云∶火郁发之是也
暑热伤气，则补而清之，东垣清暑益气汤是也。湿热之火，则或散、或渗、或下而清之，
开鬼门、清净府、除陈 是也。燥热之火，则润而清之，通大便也。伤食积热，则消而
清之，食去火自平也。惟夫伤寒传入胃腑，热势如蒸，自汗口渴，饮冷而能消水者，借非白
虎汤之类，鲜克有济也。更有阳盛拒阴之证，清药不入，到口随吐，则以姜汁些少为引，或
姜制黄连反佐以取之，所谓寒因热用是也。此外感实火之清法也。若夫七情气结，喜、怒、忧、
思、悲、恐、惊，互相感触，火从内发，丹溪治以越鞠丸，开六郁也。立斋主以逍遥散
调肝气也，意以一方治木郁而诸郁皆解也。然经云∶怒则气上，喜则气缓，悲则气消，恐
则气下，惊则气乱，思则气结。逍遥一方，以之治气上、气结者，固为相宜，而于气缓、气
消、气乱、气下之证，恐犹未合。盖气虚者，必补其气。血虚者，必滋其血。气旺血充而七
情之火悠焉以平。至若真阴不足，而火上炎者，壮水之主以镇阳光。真阳不足，而火上炎者
引火归原以导龙入海。此内伤虚火之治法也。或者曰∶病因于火，而以热药治之，何也？
不知外感之火，邪火也，人火也，有形之火，后天之火也，得水则灭，故可以水折。内伤之
火，虚火也，龙雷之火也，无形之火，先天之火也，得水则炎，故不可以水折，譬如龙得水
而愈奋飞，雷因雨而益震动，动阴蒙沉晦之气，光焰烛天，必俟云收日出而龙雷各归其宅耳。
是以虚火可补而不可泻也。其有专用参 ，而不用八味者，因其穴宅无寒也。其有专用六味
而不用桂附者，因其穴宅无水也。补则同，而引之者稍不同耳。盖外感之火，以凉为清。
内伤之火，以补为清也。
然又有清之而不量其人者何也？夫以壮实之人，而患实热之病。清之稍重，尚为无碍。
若本体素虚，脏腑本寒，饮食素少，肠胃虚滑，或产后、病后、房室之后，即有热证，亦宜
少少用之，宁可不足，不使有余；或余热未清，即以轻药代之，庶几病去人安，倘清剂过多
则疗热未已而寒生矣。此清之贵量其人也。
然又有清之不量其证者何也？夫以大热之证，而清剂太微，则病不除，微热之证，而清
剂太过，则寒证即至，但不及犹可再清，太过则将医药矣。且凡病清之而不去者，犹有法焉
壮水是也。王太仆云∶大热而甚，寒之不寒，是无水也，当滋其肾。肾水者，天真之水也
取我天真之水以制外邪，何邪不服？何热不除？而又何必沾沾于寒凉，以滋罪戾乎！由是观
之，外感之火，尚当滋水以制之，而内伤者更可知矣。大抵清火之药，不可久恃，必归本于
滋阴。滋阴之法，又不能开胃扶脾，以恢复元气，则参、苓、 、术，亦当酌量而用。非曰
清后必补，但元气无亏者，可以不补；元气有亏，必须补之。俟其饮食渐进，精神爽慧，然
后止药可也。此清之贵量其证也。总而言之，有外感之火，有内伤之火，外感为实，内伤为
虚，来路不同，治法迥别，宁曰热者寒之，遂足以毕医家之能事也乎！
清法，就是清除体内的热邪。脏腑如果有热，就用清法治疗。《内经》说：“热者寒之”，就是这个道理。然而，有的病应当用清法却没有用，从而误人；有的病不应当用清法却用了，从而误人；有的病应当用清法，但不分内伤还是外感而误人；有的病应当用清法，但不根据病人的体质强弱和证候轻重而误人，这些情况都是必须仔细辨别的。
六淫（风、寒、暑、湿、燥、火六种外感病邪）中的邪气，除了中寒、寒湿之外，大多都会导致热证。热气熏蒸，有时表现在口舌、唇齿之间，有时表现在口渴、大小便异常之际。如果明知是热证却不进行清热治疗，那么就会发生发斑、发黄、神志狂乱、四肢厥冷、呕吐、鼻衄等各种病症，层出不穷。这就是“当清不清”造成的错误。
然而，又有不应当清热却清热的情况，这是为什么呢？比如那些从事体力劳动、辛苦劳作的人，中气（脾胃之气）大虚，出现发热、倦怠、心烦、小便短赤等症状，这叫做“虚火”。这是因为春生之气不行，没有阳气来护卫营卫，这与外感的热证有着天壤之别。又有阴虚劳瘵（肺结核等慢性消耗性疾病）的证候，表现为下午定时发热（日晡潮热），以及产后血虚引起的发热烦躁，症状看起来像白虎汤证，如果误服白虎汤，很难救治。更有命门火衰，浮阳上泛，看起来像有火的假热证。还有阴盛格阳（体内阴寒过盛，逼迫阳气浮越于外），出现假热证，病人面红、狂躁，想坐在泥水中，或者几天不大便，或者舌苔黑而湿润，或者脉象反而洪大有力，在指下感觉鼓击有力，但重按却空虚无力，或者口渴想喝冷饮却无法咽下，或者因为下元（肾与膀胱等下部脏腑）虚冷，频繁饮用热汤以自救。世俗之人不懂这些，误投凉药，药一下咽就危险了。这就是“不当清而清”造成的错误。
然而，又有清热时不分内伤和外感的情况，这是为什么呢？如果是风寒闭郁导致的火热，应当发散并清热，《内经》说：“火郁发之”，就是这个意思。如果是暑热损伤元气，应当补益并清热，李东垣的清暑益气汤就是这样的方剂。如果是湿热之火，应当通过发散、渗利或攻下等方法来清热，即开鬼门（发汗）、洁净府（利小便）、去陈莝（通大便）的方法。如果是燥热之火，应当滋润并清热，即通畅大便。如果是伤食积滞化热，应当消食导滞并清热，食物积滞去除，火热自然平息。只有伤寒传入胃腑，热势如蒸笼般炽盛，自汗、口渴，能饮水且水能被消化吸收的，如果不是用白虎汤之类的方剂，很少能取得疗效。更有阳盛拒阴的证候，清热药入口即吐，这时可以用少许姜汁作为引经药，或者用姜制黄连反佐服用，这就是所谓的“寒因热用”。这是外感实火的清法。至于七情（喜、怒、忧、思、悲、恐、惊）气机郁结，互相感触，火热从内部发出的，朱丹溪用越鞠丸治疗，以开通六郁。薛立斋主张用逍遥散调理肝气，意图是用一个方子治疗木郁（肝气郁结），从而使各种郁结都得到解决。但是《内经》说：“怒则气上，喜则气缓，悲则气消，恐则气下，惊则气乱，思则气结。”逍遥散用来治疗气上、气结的证候，固然合适，但对于气缓、气消、气乱、气下的证候，恐怕就不太合拍了。大概气虚的人，必须补气；血虚的人，必须补血。气旺血充，七情之火自然平息。至于真阴不足，导致火上炎的，应当壮水之主（滋补肾阴）以抑制阳光（虚火）。真阳不足，导致火上炎的，应当引火归原，引导龙雷之火入海（回归肾宅）。这是内伤虚火的治疗方法。有人问：病因在于火，为什么用热药治疗呢？不知道外感的火，是邪火、人火、有形之火、后天之火，得水则灭，所以可以用水来折服它。内伤的火，是虚火、龙雷之火、无形之火、先天之火，得水则更旺，所以不可以用水来折服。譬如龙得到水更加奋飞，雷因为雨更加震动，触动阴晦之气，光焰烛天，必须等到云收日出，龙和雷才各自回到它们的居所。所以虚火只能补而不能泻。那些专门用人参、黄芪等补气药，而不用八味丸（金匮肾气丸）的，是因为其穴宅（身体内部环境）没有寒邪。那些专门用六味地黄丸而不用桂枝、附子的，是因为其穴宅没有水（阴液）。补益的原则是一样的，只是引导的方法稍有不同罢了。大概外感的火，以清凉为清法；内伤的火，以补益为清法。
然而，又有清热时不根据病人具体情况（体质、虚实）的情况，这是为什么呢？对于身体壮实的人，患实热病，清热药稍微重用一些，尚且无碍。如果病人本体素来虚弱，脏腑本寒，饮食素少，肠胃虚滑，或者是产后、病后、房事之后，即使有热证，也应该少量使用清热药，宁可剂量不足，不要过量；如果余热未清，就用轻量的药物代替，这样病去而人安。如果清热药过多，那么热病还没好，寒证就产生了。这就是清热贵在衡量病人的体质。
然而，又有清热时不根据证候轻重程度的情况，这是为什么呢？对于大热的证候，如果清热药量太少，病就不能除去；对于微热的证候，如果清热药量太大，寒证就会立即到来。病情轻而用药不够，还可以再次清热；用药太过，就会造成损害。而且凡是病用清热法不能去除的，还有办法，那就是“壮水”（滋补肾阴）。王冰说：“大热而甚，寒之不寒，是无水也，当滋其肾。”肾水，是天真的水。取我天真之水来制约外邪，什么邪气不服？什么热不能除？又何必执着于寒凉药物，从而增添罪过呢！由此看来，外感的火，还应当滋水来制约它，内伤的火就更不用说了。大抵清火的药物，不可长期依赖，最终必须归于滋阴。滋阴的方法，又不能开胃扶脾，以恢复元气，那么人参、茯苓、山药、白术等药，也应当酌情使用。不是说清热后一定要补，但如果元气没有亏损，可以不补；如果元气有亏损，必须补益。等到饮食逐渐增加，精神清爽聪慧，然后才可以停药。这就是清热贵在衡量证候的轻重。总而言之，有外感的火，有内伤的火，外感属于实证，内伤属于虚证，来源不同，治法截然不同，难道仅仅说“热者寒之”，就足以完备医家的能事吗！
Qing (Clearing) refers to clearing heat. When the Zang-Fu organs have heat, one should clear it. The Classic states: "For heat, use cold," which is correct. However, there are errors where treatment should be clearing but is not, causing harm; where treatment should not be clearing but is used, causing harm; where clearing is indicated but fails to distinguish between internal injury and external contraction, causing harm; and where clearing is indicated but fails to consider the patient's constitution and the severity of the syndrome, causing harm. These situations must be carefully examined.
Among the Six Excesses (Wind, Cold, Summer-heat, Dampness, Dryness, Fire), except for Cold and Cold-Dampness, all tend to cause heat syndromes. Heat qi steaming and steaming may manifest in the mouth, tongue, lips, and teeth, or during thirst and urination/defecation. If heat is clearly identified but not cleared, symptoms such as macules, jaundice, mania, cold extremities, vomiting, and epistaxis will arise in endless variety. This is the error of "failing to clear when one should."
However, why is there sometimes clearing when one should not? For example, individuals engaged in hard physical labor often suffer from severe deficiency of Middle Qi (Spleen/Stomach Qi), presenting with fever, fatigue, mental restlessness, and dark urine. This is called "Deficient Fire." It arises because the Spring-generating function fails, lacking Yang to protect Ying and Wei (Nutritive and Defensive Qi). This is worlds apart from external heat syndromes. There are also cases of Yin-deficiency consumption diseases (such as tuberculosis) presenting with tidal fever in the late afternoon, or postpartum blood deficiency causing fever and irritability. These symptoms resemble a Baihu Tang (White Tiger Decoction) syndrome; if mistakenly treated with Baihu Tang, rescue is difficult. Furthermore, there is decline of Mingmen Fire (Gate of Life Fire) with floating Yang rising, appearing like fire. There is also Yin-excess repelling Yang (Yin-Cold forcing Yang to float outward), presenting as false heat: the patient has a red face, mania, and agitation, desiring to sit in mud or water; or has constipation for several days; or has a black but moist tongue coating; or has a pulse that appears surging and large, beating vigorously under the fingers but empty upon deep pressure; or has thirst desiring cold drinks but unable to swallow them; or due to deficiency-cold in the Lower Yuan (Kidneys and Bladder), frequently drinks hot soup to save themselves. Laypeople do not understand this and mistakenly administer cooling medicines, which can be fatal upon ingestion. This is the error of "clearing when one should not."
However, why is there sometimes clearing without distinguishing between internal injury and external contraction? If Fire is closed by Wind-Cold, one should disperse and clear it, as stated in the Classic: "For constrained Fire, vent it." If Summer-heat damages Qi, one should tonify and clear it, as in Li Dongyuan's Qingshu Yiqi Tang (Clear Summer-heat and Boost Qi Decoction). If it is Fire from Damp-Heat, one should clear it through dispersing, leaching out, or purging methods, i.e., opening the ghost gates (sweating), cleansing the pure mansion (urination), and removing old filth (bowel movement). If it is Fire from Dryness-Heat, one should moisten and clear it by unblocking the bowels. If it is accumulated food generating heat, one should digest and clear it; once the food is removed, the fire calms naturally. Only when Shaoyang disease transmits to the Stomach Fu organ, with heat intense like steaming, spontaneous sweating, thirst, and the ability to drink cold water and digest it, is a formula like Baihu Tang (White Tiger Decoction) rarely ineffective. In cases of Yang-excess repelling Yin, where cooling medicines are rejected and vomited immediately upon ingestion, a small amount of Ginger Juice can be used as a guide, or Ginger-processed Huanglian (Coptis Rhizome) can be used for counter-assistance, known as "using cold for heat." This is the method of clearing external excess Fire. Regarding Fire arising internally from emotional constraint (Joy, Anger, Worry, Thought, Sorrow, Fear, Fright) interacting with each other, Zhu Danxi treated it with Yueju Wan (Regulate All Pill) to open the Six Constraints. Xue Lizhai advocated Xiaoyao San (Free and Easy Wanderer Powder) to regulate Liver Qi, intending that treating Wood constraint would resolve all constraints. However, the Classic states: "Anger causes Qi to rise, Joy causes Qi to slacken, Sorrow causes Qi to dissipate, Fear causes Qi to descend, Fright causes Qi to become chaotic, Thought causes Qi to knot." Xiaoyao San is suitable for rising and knotted Qi, but likely inappropriate for slackening, dissipating, chaotic, or descending Qi. Generally, for Qi deficiency, one must tonify Qi; for Blood deficiency, one must nourish Blood. When Qi is vigorous and Blood is abundant, Fire from the Seven Emotions naturally calms. For insufficiency of True Yin causing Fire to flare upward, one must strengthen the Master of Water (nourish Kidney Yin) to suppress Solar Fire. For insufficiency of True Yang causing Fire to flare upward, one must guide Fire back to its source, leading the Dragon and Thunder into the sea. This is the treatment method for internal deficient Fire. Some ask: If the disease is caused by Fire, why treat with hot medicines? One must know that external Fire is pathogenic, human, tangible, and postnatal Fire; it is extinguished by water, so it can be subdued by water. Internal Fire is deficient, Dragon-Thunder, intangible, and prenatal Fire; it flares up with water, so it cannot be subdued by water. It is like a dragon flying higher when it gets water, or thunder shaking more intensely with rain, stirring up yin obscurity, illuminating the sky; only when clouds gather and sun emerges do the dragon and thunder return to their homes. Therefore, deficient Fire can be tonified but not purged. Those who use only Renshen (Ginseng Root) and Huangqi (Astragalus Root) without Bajun Wan (Eight-Ingredient Pill) do so because their dwelling place lacks cold. Those who use only Liuwei Dihuang Wan (Six-Ingredient Rehmannia Pill) without Guizhi (Cinnamon Twig) and Fuzi (Aconite Root) do so because their dwelling place lacks water. The principle of tonification is the same, but the guiding method differs slightly. Essentially, external Fire is cleared with coolness; internal Fire is cleared with tonification.
However, why is there sometimes clearing without considering the patient's condition? For robust individuals suffering from excess heat, using slightly heavier clearing agents is harmless. But for those constitutionally weak, with inherently cold Zang-Fu, poor diet, and loose bowels, or those postpartum, post-illness, or post-coitus, even if heat syndromes exist, clearing agents should be used sparingly. It is better to under-dose than over-dose. If residual heat remains, light agents should substitute. Thus, the disease leaves and the person remains safe. If clearing agents are excessive, cold will arise before the heat is fully resolved. This emphasizes weighing the patient when clearing.
However, why is there sometimes clearing without considering the syndrome's severity? For severe heat syndromes, if the clearing agent is too weak, the disease persists; for mild heat syndromes, if the clearing agent is too strong, cold syndromes will appear. If the dose is insufficient, one can clear again; if excessive, harm results. Moreover, for diseases not resolved by clearing, there is another method: strengthening Water (nourishing Yin). Wang Bing said: "Severe heat that does not respond to cold treatment indicates lack of Water; one should nourish the Kidney." Kidney Water is pristine Water. Using this pristine Water to control external pathogens, what pathogen would not submit? What heat would not be eliminated? Why cling to cold and cool herbs, thereby incurring fault? From this, we see that even external Fire should be controlled by nourishing Water, let alone internal Fire. Generally, fire-clearing drugs should not be relied upon long-term; one must ultimately return to nourishing Yin. Nourishing Yin methods must also open the stomach and support the Spleen to restore Yuan Qi. Therefore, Renshen (Ginseng Root), Fuling (Poria), Shanyao (Dioscorea Rhizome), and Baizhu (Atractylodes Macrocephala Rhizome) should be used judiciously. It is not that one must always tonify after clearing; if Yuan Qi is intact, tonification is unnecessary; if Yuan Qi is depleted, it must be tonified. Wait until appetite gradually returns and spirit becomes bright and alert before stopping medication. This emphasizes weighing the syndrome when clearing. In summary, there is external Fire and internal Fire. External is excess; internal is deficiency. Their origins differ, and their treatments are distinct. Can one say that "for heat, use cold" suffices to complete the physician's duties?