世人皆曰水克火，而余独曰水养火。世人皆曰金生水，而余独曰水生金。世人皆曰土克水，而余独于
水中补土。世人皆曰本克土，而余独升木以培土。何则？君相二火，以肾为宫，水克火者，后天有形之水
火也；水养火者，先天无形之水火也。肺金之气，夜卧则归藏于肾水之中，丹溪谓之母藏子宫，子隐母胎。
此一脏名曰娇脏，畏热而畏寒。肾中有火，则金畏火刑而不敢归；肾中无火，则水冷金寒而不敢归。或
为喘胀，或为咳嗽，或为不寐。或为不食。斯时欲补土，母以益子，喘胀愈甚。清之泻之，肺气日消，
死期迫矣。惟收敛一法，仅似有理，然不得其门，从何而入？夫肺出气也，肾纳气也，肺为气之主，
肾为气之本，凡气从脐下逆奔而上者，此肾虚不能纳气归元也。毋徒从事于肺，或壮水之主，或益
火之原，金向水中生矣，若夫土者随火寄生，即当随火而补。然而补火有至妙之理，阳明胃土随少阴心
火而生，故补胃土者补心火。而归脾汤一方，又从火之外家而补之，俾木生火，火生土也。太阴脾土，
随少阳相火而生，故补脾土者补相火。而八味丸一方，合水火既济而蒸腐之，此一理也。张仲景立
建中汤以健脾土，木曰曲直，曲直作酸，芍药味酸为甲木；土曰稼穑，稼穑作甘，甘草味甘作己土。酸甘
相合，甲己化土。又加肉桂，盖桂属龙火，使助其化也。仲景立方之妙类如此。又以见木生土之义，
世以木克土，举欲伐之，不知木气者，生生之气也，阳气也，元气也，胃气也，同出而异名者也，焉
可伐之，此东垣《脾胃论》用升柴以疏木气，谆谆言之详也。
龙雷之火，无形而有声，不焚草木，得雨而益炽，见于季春而伏于季秋。原夫龙雷之见者，以五月
一阴生，水底冷而天上热，龙为阳物，故随阳而上升。至冬至一阳来复，故龙亦随阳而下伏，雷亦收声。
人身肾中相火亦犹是也。平日不能节欲，以致命门火衰，肾中阴盛，龙火无藏身之位，故游于上而不归，
是以上焦烦热，咳嗽等症。善治者，以温肾之药从其性而引之归原，使行秋冬阳伏之令，而龙归大海，此
至理也。奈何今之治阴虚火衰者，以黄柏。知母为君，而愈寒其肾，速其毙，良可悲哉！若有阴虚火旺者
，此肾水干枯而火偏盛，宜补水以配火，亦不宜苦寒之品以灭火。壮水之主，以镇阳光，正谓此。
坎干水也，气也，即小而井，大而海也。兑坤水也，即微而露，大而雨也。一阳陷于二阴为坎，
坎以水气，潜行地中，为万物受命根本，故曰润万物者，莫润乎水。一阴上彻于二阳为兑，兑以有形
之水，普施于万物之上，为资生之利泽，故曰说万物者，莫说乎泽明。此二水可以悟治火之道矣。
心火者，有形之火也；相火者，无形之火也。无形之火由燥热而津液枯，以五行有形之兑水制之者，权
也。吾身自有上池之水气也，无形者也，以无形之水，沃无形之火，常而可久者也。是为真水真火，升降
即宜，而成既济矣。
世人常说水克火，而我唯独认为水能养火。世人常说金生水，而我唯独认为水生金。世人常说土克水，而我唯独主张在水中补土。世人常说木克土，而我唯独主张升举木气以培补脾土。为什么呢？君火与相火，以肾脏为宫室；所谓“水克火”，指的是后天有形的水火关系；所谓“水养火”，指的是先天无形的水火关系。肺金之气，在夜间睡眠时则归藏于肾水之中，朱丹溪称之为“母藏子宫，子隐母胎”。这一脏器被称为娇脏，既怕热又怕寒。如果肾中有火，肺金就会畏惧火的刑克而不敢回归；如果肾中没有火，水冷金寒，肺金也不敢回归。这会导致气喘肿胀，或者咳嗽，或者失眠，或者食欲不振。在这个时候，如果想通过补土（母）来益子（肺），喘胀症状会更加严重。如果用清热泻火的方法，肺气日渐消损，死亡的日子就近了。只有收敛这一法，看起来似乎有理，但如果找不到门径，从何处进入呢？肺主呼气，肾主纳气，肺是气的主宰，肾是气的根本。凡是气从脐下逆奔而上的人，这是肾虚不能纳气归元。不要只专注于治肺，或者滋补肾阴（壮水之主），或者温补肾阳（益火之原），这样金就能在水中生化了。至于土，是随火而寄生的，就应当随火而补。然而补火有极其精妙的道理，阳明胃土随着少阴心火而生，所以补胃土就是补心火。而归脾汤一方，则是从火的外围来补益，使得木生火，火生土。太阴脾土，随着少阳相火而生，所以补脾土就是补相火。而八味丸一方，融合了水火既济的原理来蒸腐运化，这是一个道理。张仲景创立建中汤来健脾土，木的特性是曲直，曲直产生酸味，芍药味酸属于甲木；土的特性是稼穑，稼穑产生甘味，甘草味甘属于己土。酸甘相互结合，甲己化土。又加入肉桂，因为桂属龙火，用来帮助其化生。张仲景立方的精妙大多如此。这也体现了木生土的道理。世人认为木克土，都想伐除木气，却不知道木气是生生之气、阳气、元气、胃气，它们同出而异名，怎么可以伐除它呢？这就是李东垣《脾胃论》中反复详细论述的用升麻、柴胡来疏达木气的道理。
龙雷之火，无形而有声，不焚烧草木，遇到雨水反而更加炽盛，出现在晚春而潜伏在晚秋。推究龙雷显现的原因，是因为五月一阴初生，水底寒冷而天上炎热，龙是阳物，所以跟随阳气而上升。到了冬至一阳来复，所以龙也跟随阳气而下伏，雷也收起声音。人身中的肾中相火也是如此。平日不能节制欲望，导致命门火衰，肾中阴盛，龙火没有藏身的位置，所以游荡在上部而不能回归，所以上焦烦热、咳嗽等症状出现。善于治疗的人，用温肾的药物顺从其本性而引导它回归本源，使其执行秋冬阳气潜伏的规律，从而龙归大海，这是至理。奈何现在治疗阴虚火衰的人，把黄柏、知母作为主药，结果使肾脏更寒，加速死亡，实在可悲啊！如果有阴虚火旺的情况，这是肾水干枯而火偏盛，应该补水以配火，也不宜用苦寒的药物来灭火。“壮水之主，以镇阳光”，正是说的这个意思。
坎卦代表水，代表气，即小如井水，大如海水。兑卦和坤卦代表水，即微小如露水，大如雨水。一阳陷于二阴之间形成坎卦，坎卦以水气潜行地中，是万物受命的根本，所以说滋润万物的，没有比水更滋润的了。一阴上彻于二阳之间形成兑卦，兑卦以有形之水，普遍施利于万物之上，是资生的利泽，所以说喜悦万物的，没有比泽更喜悦的了。明白这两种水，就可以领悟治疗火道的原理了。
心火，是有形的火；相火，是无形的火。无形的火由燥热导致津液枯竭，用五行中有形的兑水来制约它，是权宜之计。我们身体自有上池之水气，是无形的，用无形之水去浇灌无形之火，是常规且可长久的方法。这就是真水真火，升降适宜，从而达成既济的状态。
People generally say that Water overcomes Fire, but I alone assert that Water nourishes Fire. People generally say that Metal generates Water, but I alone assert that Water generates Metal. People generally say that Earth overcomes Water, but I alone advocate tonifying Earth within Water. People generally say that Wood overcomes Earth, but I alone advocate raising Wood Qi to cultivate Earth. Why is this? The Ministerial Fire and Sovereign Fire take the Kidney as their palace; what is called "Water overcomes Fire" refers to the postnatal, tangible Water and Fire; what is called "Water nourishes Fire" refers to the prenatal, intangible Water and Fire. The Qi of Lung Metal returns and stores itself in Kidney Water during sleep at night; Zhu Danxi calls this "the mother hides in the womb, the child conceals in the mother's fetus." This organ is known as the Delicate Organ, fearing both heat and cold. If there is Fire in the Kidney, Lung Metal will fear being punished by Fire and dare not return; if there is no Fire in the Kidney, the Water becomes cold and Metal becomes chilled, so Lung Metal also dares not return. This may result in wheezing and distension, or coughing, or insomnia, or loss of appetite. At such times, if one attempts to tonify Earth (the Mother) to benefit the Child (Lung), the wheezing and distension will worsen. Using methods to clear and purge will cause Lung Qi to diminish daily, bringing death closer. Only the method of astringency seems reasonable, but without finding the entry point, how can one proceed? The Lung exhales Qi, while the Kidney receives Qi; the Lung is the master of Qi, and the Kidney is the root of Qi. Whenever Qi rebels and rushes upward from below the umbilicus, this is due to Kidney deficiency failing to receive and anchor Qi into its origin. One should not merely focus on treating the Lung; rather, one should either strengthen the Master of Water (Zhuang Shui Zhi Zhu) or benefit the Origin of Fire (Yi Huo Zhi Yuan), so that Metal is generated within Water. As for Earth, it parasitically exists following Fire, so it should be tonified following Fire. However, there is an exquisite principle in tonifying Fire: Yangming Stomach Earth is generated following Shaoyin Heart Fire, thus tonifying Stomach Earth is equivalent to tonifying Heart Fire. The Guipi Tang (Return to the Spleen Decoction) tonifies from the outer realm of Fire, allowing Wood to generate Fire, and Fire to generate Earth. Taiyin Spleen Earth is generated following Shaoyang Ministerial Fire, thus tonifying Spleen Earth is equivalent to tonifying Ministerial Fire. The Bawei Wan (Eight-Ingredient Pill) integrates the mutual completion of Water and Fire to steam and rot (digest), which is one principle. Zhang Zhongjing established Jianzhong Tang (Middle-Jian Decoction) to strengthen Spleen Earth. Wood is characterized by bending and straightening, producing sourness; Shaoyao (Radix Paeoniae Rubra/Alba) is sour and belongs to Jia Wood. Earth is characterized by sowing and reaping, producing sweetness; Gancao (Radix Glycyrrhizae) is sweet and belongs to Ji Earth. Sour and Sweet combine, and Jia and Ji transform into Earth. Adding Rougui (Cortex Cinnamomi) is because Gui belongs to Dragon Fire, assisting its transformation. The subtlety of Zhang Zhongjing's prescriptions is largely like this. This also reveals the meaning of Wood generating Earth. People believe Wood overcomes Earth and wish to chop it down, unaware that Wood Qi is the Qi of generation, Yang Qi, Primordial Qi, and Stomach Qi; they share the same origin but have different names. How can they be chopped down? This is why Li Dongyuan's *Pi Wei Lun* (Treatise on the Spleen and Stomach) earnestly and detailedly discusses using Shengma (Rhizoma Cimicifugae) and Chaihu (Radix Bupleuri) to soothe Wood Qi.
Dragon and Thunder Fire is intangible yet audible; it does not burn vegetation but intensifies with rain; it appears in late spring and lies dormant in late autumn. Investigating the appearance of Dragon and Thunder: in the fifth month, Yin begins to arise, making the water bottom cold and the sky hot. Since Dragons are Yang entities, they rise with Yang. At the Winter Solstice, Yang returns, so Dragons also submerge with Yang, and Thunder ceases its sound. The Ministerial Fire in the Kidneys of the human body is exactly the same. In daily life, failure to restrain desires leads to the decline of Mingmen Fire and excess Yin in the Kidneys. With no place for Dragon Fire to reside, it wanders upward and fails to return, resulting in upper jiao irritant heat, coughing, and other symptoms. A skilled practitioner uses warming Kidney medicines to follow its nature and guide it back to its origin, allowing it to execute the command of Yang lying dormant in Autumn and Winter, thus returning the Dragon to the sea; this is the supreme principle. Alas, how sad that nowadays, when treating Yin deficiency with Fire decline, practitioners use Huangbai (Cortex Phellodendri) and Zhimu (Rhizoma Anemarrhenae) as chief ingredients, thereby further chilling the Kidneys and hastening demise! If there is Yin deficiency with Fire hyperactivity, this is due to dryness and depletion of Kidney Water with excessive Fire; one should tonify Water to harmonize with Fire, and should not use bitter-cold substances to extinguish the Fire. "Strengthening the Master of Water to suppress the Solar Flare" precisely refers to this.
Kan represents Water and Qi, small like well water, large like ocean water. Dui and Kun represent Water, minute like dew, large like rain. One Yang trapped between two Yins forms Kan; Kan moves underground with Water Qi, serving as the fundamental source of life for all things, hence it is said: "Nothing moistens the ten thousand things more than Water." One Yin penetrating through two Yangs forms Dui; Dui spreads tangible Water above all things, providing beneficial nourishment for creation, hence it is said: "Nothing delights the ten thousand things more than Marsh." Understanding these two types of Water allows one to comprehend the way of treating Fire.
Heart Fire is tangible Fire; Ministerial Fire is intangible Fire. Intangible Fire causes fluid depletion due to dryness and heat; using tangible Dui Water from the Five Elements to control it is a provisional measure. Our body possesses Shangchi Water Qi, which is intangible; using intangible Water to irrigate intangible Fire is the constant and enduring method. This constitutes True Water and True Fire; when their ascending and descending are appropriate, Mutual Completion (Ji Ji) is achieved.