前人每于阴虚阳陷，热郁于内，脉见沉散之证；阴虚阳亢，热浮于外，脉见浮洪之证；
阴虚
阳熄，内外皆寒，脉见芤弦之证；阳虚内陷，阴为阳扰，脉见紧数之证，一概指为阴证。与
阴
盛格阳，寒冱于内；阴盛遏阳，寒锢于外之证，略无分别。此喻嘉言所讥为传派不清者也。
倘概用附子理中、四逆、真武，贻误岂浅鲜哉!更有口称阴证，而方用四物、六味；口称
阴
虚，而方用四逆、白通者，尤当会意，勿致害词。夫阴虚者阳必凑之，阳虚者阴必凑之，此
一说也；阴虚者阳必无根，阳虚者阴必不固，此又一说也。故阳虚内热，与阴虚内热，致不
同也。阴虚者，如房室过度，或用心过度，阴气消耗，发为骨蒸，骨髓如空，小便赤涩，
此阴虚而阳气因以陷之也。治之必填精补血，以充其阴而擎其阳，宣发升举之品，只可为佐
。阳虚者，如劳力过度，汗出过多，一经宁息，时时洒淅恶寒，内发烦渴，四肢困倦，筋骨
酸，此阳虚不能行表，而内缩于阴也，此时阴分亦必受伤，但病起于阳。治之必健脾益气
，以充壮其阳，生津清热之品，亦只可为佐。东垣补中益气之制，为阳虚内热设也。丹溪大
补阴丸之制，为阴虚内热设也；二者岂可差互乎?重以填精补血治阳虚，必致阳愈郁滞，而
不可复振；重以健脾益气治阴虚，必致阴愈消灼，而不可复回。
前人对于阴虚而阳气下陷、热邪郁结于内，脉象呈现沉散之证；阴虚而阳气亢盛、热邪浮越于外，脉象呈现浮洪之证；阴虚而阳气熄灭，内外皆寒，脉象呈现芤弦之证；阳虚而内陷，阴气被阳气所扰，脉象呈现紧数之证，一概将其指认为阴证。这与阴气盛极格拒阳气、寒气凝结于内；阴气盛极遏制阳气、寒气固结于外的证候，几乎没有分别。这正是喻嘉言所讥讽的“传派不清”（辨证分类混乱）。如果一概使用附子理中汤、四逆汤、真武汤，造成的延误和危害难道还少吗！更有甚者，口称是阴证，却方剂使用四物汤、六味地黄丸；口称是阴虚，却方剂使用四逆汤、白通汤的，尤其应当领会其意旨，不要因言辞误导而致害。
所谓阴虚者，阳气必然凑集于此，这是其中一种说法；阴虚者，阳气必然无根，这是另一种说法。因此，阳虚导致的内热与阴虚导致的内热，成因是不同的。阴虚的情况，如房事过度，或用脑过度，导致阴气消耗，引发骨蒸（阴虚发热），骨髓空虚，小便赤红涩痛，这是阴虚而阳气因而陷入其中的表现。治疗时必须填补精髓、补益血液，以充实其阴气并涵养其阳气，宣发升举的药物，只能作为辅助。阳虚的情况，如劳力过度，出汗过多，一旦安静休息，便时时感到洒淅恶寒，内部出现烦渴，四肢困倦，筋骨酸痛，这是阳虚不能行于体表，而向内收缩于阴分的表现，此时阴分也必定受伤，但病起于阳虚。治疗时必须健脾益气，以充壮其阳气，生津清热的药物，也只能作为辅助。李东垣的补中益气汤的制方，是为阳虚内热设立的；朱丹溪的大补阴丸的制方，是为阴虚内热设立的；这两者岂可混淆互换呢？如果用填精补血的方法治疗阳虚，必然导致阳气更加郁滞，而无法重新振奋；如果用健脾益气的方法治疗阴虚，必然导致阴气更加消灼，而无法恢复。
Predecessors generally categorized as Yin syndromes (Yin syndromes) the following conditions: deficiency of Yin with sinking of Yang, heat constrained internally, presenting with a deep and scattered pulse; deficiency of Yin with hyperactivity of Yang, heat floating externally, presenting with a floating and surging pulse; deficiency of Yin with extinction of Yang, cold in both interior and exterior, presenting with a knotted and wiry pulse; deficiency of Yang with internal sinking, Yin disturbed by Yang, presenting with a tight and rapid pulse. These were indiscriminately labeled as Yin syndromes, without distinguishing them from conditions where excess Yin repels Yang with cold congealing internally, or excess Yin obstructs Yang with cold consolidating externally. This is what Yu Jiayan criticized as "unclear transmission lineage" (unclear differentiation of syndrome categories). If one were to indiscriminately use Fuzi Lizhong Decoction (Aconite and Ginger Decoction for Spleen and Stomach), Sini Decoction (Recovery from Reversal Decoction), or Zhenwu Decoction (True Warrior Decoction), the resulting harm would be significant! Furthermore, there are those who verbally claim it is a Yin syndrome but prescribe Siwu Decoction (Four Substance Decoction) or Liuwei Dihuang Wan (Six-Ingredient Rehmannia Pill); or who verbally claim Yin deficiency but prescribe Sini Decoction or Baitong Decoction (White Through Decoction). One must grasp the underlying principles to avoid being misled by words and causing harm.
It is said that when Yin is deficient, Yang inevitably congregates there; this is one perspective. It is also said that when Yin is deficient, Yang inevitably lacks root; this is another perspective. Therefore, the internal heat caused by Yang deficiency differs from that caused by Yin deficiency. In cases of Yin deficiency, such as excessive sexual activity or excessive mental exertion, Yin Qi is depleted, leading to bone-steaming fever (bone-steaming sensation due to Yin deficiency), emptiness of the marrow, and dark, scanty, painful urination. This represents Yin deficiency with subsequent sinking of Yang. Treatment requires filling the essence and nourishing blood to replenish Yin and anchor Yang; herbs that promote dispersing and ascending should only be used as adjuvants. In cases of Yang deficiency, such as excessive physical labor or profuse sweating, upon resting, one experiences chills and aversion to cold, internal irritability and thirst, fatigue in the four limbs, and soreness/aching in bones and sinews. This represents Yang deficiency failing to circulate on the exterior, retreating inward into Yin. At this time, the Yin aspect is also injured, but the pathology originates from Yang deficiency. Treatment requires strengthening the Spleen and augmenting Qi to bolster Yang; herbs that generate fluids and clear heat should only be used as adjuvants. Li Dongyuan's Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction) was formulated for internal heat due to Yang deficiency; Zhu Danxi's Da Bu Yin Wan (Great Tonification of Yin Pill) was formulated for internal heat due to Yin deficiency. Can these two be confused? If one heavily uses methods of filling essence and nourishing blood to treat Yang deficiency, it will inevitably cause further stagnation of Yang, making it impossible to revive; if one heavily uses methods of strengthening the Spleen and augmenting Qi to treat Yin deficiency, it will inevitably cause further consumption and burning of Yin, making it impossible to restore.