经曰∶君火以明，相火以位。此就火德辨阴阳，而悉其形气之理也。盖火本阳也，而阳
之在上者，为阳中之阳，故曰君火。阳之在下者，为阴中之阳，故曰相火。此天地生成之道
也。其在于人，则上为君火，故主于心。下为相火，故出于肾。主于心者，为神明之主，故
曰君火以明。出于肾者，为发生之根，故曰相火以位。至其为病，则以明者，其化虚，故君
火之气，有晦有明。以位者，其化实，故相火之病，能焚能燎。何也？盖化虚者，无形者也
，故其或衰或王，惟见于神明，神惟贵足，衰则可畏也。化实者，有形者也。故其为热为寒
，必着于血气，确有证据，方可言火也。此其一清一浊，有当辨者如此。然清浊虽二，而气
禀则一。故君火衰则相火亦败，此以无形者亏及有形者也；相火炽则君火亦炎，此以有形者
病及无形者也。夫生以神全，病惟形见，故火邪之为病，必根据于有位有形之相火。所谓邪火
者，即所谓凡火也，即所谓燎原之火也。惟不得其正，所以为病。故别以邪火名之，而实非
可以君相并言也。故在《内经》则又谓之畏火。正以此火有形，故可畏也。夫病以有形之火
，须治以有形之物，故形而火盛者，可泻以苦寒之物；形而火衰者，可助以甘温之物。此以
形治形，而治火之道，止于是矣。至若无形之火，则生生息息，窈窈冥冥，为先天之化，为
后天之神，为死生之母，为玄牝之门。又岂于形迹之间可能摹拟者哉。故有形之火不可纵，
无形之火不可残。有能知火之邪正，而握其盈虚伸缩之权者，则神可全，病可却，而生道在
我矣，即吾有形，吾又何患。
《内经》说：君火以光明为用，相火以守位为职。这是从火的德性来辨别阴阳，从而通晓其形体与气机的道理。大概火本属阳，但位于上部的阳，是阳中之阳，所以称为君火。位于下部的阳，是阴中之阳，所以称为相火。这是天地生成的规律。在人体中，上部为君火，所以由心所主。下部为相火，所以出于肾。由心所主的君火，是神明的主宰，所以说是“君火以明”。出于肾的相火，是生命发生的根源，所以说是“相火以位”。
至于它们致病的情况，因为君火化生虚无（无形），所以君火之气，有时昏暗有时明亮。因为相火化生实有（有形），所以相火之病，能焚烧蔓延。为什么呢？因为化生虚无的，是无形的，所以它的或衰弱或旺盛，只表现在神志方面，神志贵在充足，衰弱了就值得畏惧了。化生实有的，是有形的，所以它表现为热或寒，必然附着在血气上，确有证据，才可以称之为火。这清与浊的区别，有应当辨别的像这样之处。然而清与浊虽然分为两类，但气的禀赋则是统一的。所以君火衰弱则相火也会败坏，这是无形的亏损波及有形的；相火炽盛则君火也会炎上，这是有形的病变波及无形的。
人生依靠神志健全，生病则只有形体显现，所以火邪致病，必须依据有位、有形的相火。所谓的邪火，就是所谓的凡火，也就是所谓的燎原之火。只是不得其正，所以才成为疾病。因此另外命名为邪火，实际上并不能与君火、相火并列谈论。所以在《内经》中又称之为畏火。正因为这种火是有形的，所以才令人畏惧。
既然病是由有形的火引起的，就必须用有形的药物来治疗，所以形体上火盛的，可以用苦寒的药物来泻火；形体上火衰的，可以用甘温的药物来助火。这是以形治形，而治疗火的方法，也就到此为止了。至于无形的火，则生生不息，幽深微妙，它是先天的化育，后天的神志，死生的母亲，玄牝之门。又岂能在形迹之间可以描摹模拟的呢？所以有形的火不可放纵，无形的火不可残害。能够知道火的邪正，并掌握其盈虚伸缩权柄的人，那么神志就可以保全，疾病就可以祛除，而生命的道就在自己手中了，即使我有形体，我又有什么可担忧的呢。
The *Neijing* (Inner Canon) states: "Jun Fire (Ministerial Fire/Heart Fire) manifests through clarity, while Xiang Fire (Ministerial Fire/Kidney Fire) functions through its position." This distinguishes Yin and Yang based on the virtue of fire, thereby comprehending the principles of form and Qi. Generally, fire belongs to Yang; however, the Yang located above is Yang within Yang, thus it is called Jun Fire (Heart Fire). The Yang located below is Yang within Yin, thus it is called Xiang Fire (Kidney Fire). This is the way of Heaven and Earth's generation. In humans, the upper part is Jun Fire, therefore it is governed by the Heart. The lower part is Xiang Fire, therefore it originates from the Kidney. That which is governed by the Heart serves as the master of Shen (Spirit/Mind), hence it is said that "Jun Fire manifests through clarity." That which originates from the Kidney serves as the root of generation, hence it is said that "Xiang Fire functions through its position."
Regarding their pathology, because Jun Fire transforms into the formless (Xu), its Qi may be obscure or clear. Because Xiang Fire transforms into the formed (Shi), its pathology can burn and blaze. Why? Because that which transforms into the formless is without physical shape; thus, its decline or flourishing is only seen in the Shen (Spirit). The Shen values sufficiency; when deficient, it is fearful. That which transforms into the formed has physical substance; thus, whether it presents as heat or cold, it must adhere to Blood and Qi, providing concrete evidence before it can be termed "Fire." Thus, the distinction between Clear and Turbid requires differentiation as described. However, although Clear and Turbid are two aspects, the endowment of Qi is one. Therefore, if Jun Fire declines, Xiang Fire also fails; this is the deficiency of the formless affecting the formed. If Xiang Fire blazes, Jun Fire also flares; this is the pathology of the formed affecting the formless. Life depends on the completeness of Shen, while disease manifests only in the Form. Therefore, the pathogenic action of Fire must rely on the positioned and formed Xiang Fire. What is called "Pathogenic Fire" is what is called "Ordinary Fire," or "Fire that spreads like a prairie fire." It becomes pathological only when it deviates from correctness. Hence, it is separately named Pathogenic Fire, but in reality, it cannot be discussed alongside Jun and Xiang Fires. Thus, in the *Neijing*, it is also called "Feared Fire." Precisely because this Fire is formed, it is feared.
Since diseases arise from formed Fire, they must be treated with formed substances. Therefore, if Fire is excessive in the Form, it can be purged with Bitter-Cold substances; if Fire is deficient in the Form, it can be assisted with Sweet-Warm substances. This is treating Form with Form, and the method of treating Fire ends here. As for Formless Fire, it generates life continuously, profound and mysterious. It is the transformation of Pre-Heaven, the Shen of Post-Heaven, the mother of life and death, and the gate of the Mysterious Female (Xuan Pin). How could it possibly be simulated within traces of form? Therefore, formed Fire must not be indulged, and formless Fire must not be destroyed. One who can discern the righteousness or pathogenicity of Fire and grasp the power of its fullness, emptiness, expansion, and contraction, will preserve the Shen, dispel disease, and hold the Dao of life in their hands. Even with a physical body, what is there to worry about?