夫阴阳之体，曰干与坤；阴阳之用，曰水与火；阴阳之化，曰形与气。以生杀言，则阳生阴杀；
以寒热言，则阳热阴寒。若其生化之机，则阳先阴后，阳施阴受。先天因气以化形，阳生阴也；后天因
形以化气，阴生阳也。形即精，精即水；神即气，气即火。阴阳二气，最不宜偏，平则气和而
生物，偏则气乖而杀物。经曰∶阴平阳秘，精神乃治；阴阳离决，精气乃绝。此先王教人察阴阳、保生
气也。
夫阳一而阴二，故偶者阴也，后天之形也；奇者阳也，先天之气也。神由气化，而气本于天，所以发生
吾身者，即真阳之气也；形以精成，而精生于气，所以成立吾身者，即真阴之气也。上古天真论曰∶
女子二七而天癸至，男子二八而天癸至。非阴生在后而阴成之难乎？阴阳应象大论曰∶人年
四十而阴气自半也。非阴衰在前而阴凋之易乎？故人全盛之数，惟二八之后，以至四旬之外，前后止二十
余年而形体渐衰矣。
阳道常实，阴道常虚，故丹溪引日月之盈亏，以为阳常
有余、阴常不足之论，而立补阴、大补等丸。独惜以黄柏、知母为神丹，致家传户用。殊不知天癸之未至
，本由乎气，而阴阳之自半，亦由乎气。是形虽在阴，而气则仍从乎阳也。此生死之机，不可不辨。
阳之为义大矣。夫阴以阳为主，所关乎造化之原，而为性命之本者，惟斯而已。姑辨其最要者，一
曰形气，二曰寒热，三曰水火。
夫形气者，阳化气，阴成形，是形本属阴，而凡通体之温者，阳气也；一生之活者，阳气也；五官五脏
之神明不测者，阳气也。乃其灵觉尽灭，身冷如冰，形固存而气则去，此以阳脱在前，而留阴在后，非
阴多于阳乎？是形气阴阳之辨也。
寒热者，春夏之暖为阳，秋冬之冷为阴。当长夏之暑，草木昆虫，咸苦煎炙，然愈炙愈繁，不热则不盛
。至一夕风霜，即僵枯遍野，是热能生物，寒无生意，热无伤而寒可畏，非
寒强于热乎？此寒热阴阳之辨也。
水火者，造化之权，其象有四∶日为太阳，火为少阳，水为太阴。月为少阴。此四象之真形也。阳中无
太阴，阴中无太阳，此阴阳之专主也。日丽乎天，此阳之阳也，非太阳乎？月之在天，阳中之阴也，非少阴
乎？水行于地，阴之阴也，非太阴乎？火之在地，阴中之阳也，非少阳乎？此等大义，丹溪所未知，故引日
月盈亏，以证阴阳虚实。况夫阴阳之性，太者气刚，故日不可灭，水不可竭，此日为火之本，水为月之
根也；少者气柔，故火有时息，月有时缺，此火为日之余，月为水之余也。惟其不灭者，乃为真火；而时作
时止，岂即元阳？故惟真阳之火，乃能生物；而燎原之凡火，但能焦物也。夫天一生水，天一者，天之一也
，一即阳也，无一则止于六
耳。故水之生物者，赖此一也；水之化气者，赖此一也。故春夏之水，土得之而生长；秋冬之水，土得之
而不生不长，是水亦死矣，水之所以生，水之所以行，孰非阳所主？此水中有阳，非水即为阳也。
夫阳气不充，则生意不广，而况于无阳乎？故阳惟畏其衰，阴惟畏其盛，非阴能自盛也，阳衰则阴盛矣。
凡万物之生由乎阳，万物之死亦由乎阳。非阳能死物也，阳来则生，阳去则死矣。试以太阳证之∶日行南
陆，在时为冬，斯时非无日也，第稍远耳，便见严冬难御，万物凋零。然则天地之和，惟此日也；万物之生，
惟此日也。设无此日，天地虽大，一寒质耳，人是小乾坤，得阳则生，失阳则死。阳衰者，即亡阳之渐也。
圣人作《易》，首制一爻，立元阳之祖，明阳德之元亨于坤初六，日履霜坚冰，虑阴气之渐长，防其
有妨化育耳。
《内经》曰∶凡阴阳之要，阳密乃固。此言阴之所恃，阳为主也。又曰∶阳气者若天与日，失其所则折
寿而不彰，故天运当以日光明。可见人之大宝，只此一息真阳，孰谓阳常有余，而欲以苦寒之物，伐此阳
气，欲保生可如是乎？
客曰∶欲固此阳，计将安出？曰∶但知根本，此其要也，命门是也。所谓命门者，先天之生我，由此
而受；后天之我生，由此而栽也，夫生之门即死之户，人之盛衰安危，皆系于此。以其为生气之源，而气强
则强，气衰则病，此虽至阴之地，而实元阳之宅。至夫脾胃，乃后天水谷之本，犹属元阳之子耳。
阴阳的本体，称为乾与坤；阴阳的作用，称为水与火；阴阳的化生，称为形与气。从生长与肃杀的角度来说，阳气主生，阴气主杀；从寒热的属性来说，阳热而阴寒。至于它们生化运作的机理，则是阳气先行、阴气后随，阳气施予、阴气受纳。先天阶段，因气而化生为形，这是阳生阴；后天阶段，因形而化生为气，这是阴生阳。形就是精，精就是水；神就是气，气就是火。阴阳二气，最忌讳偏颇，平衡则气和顺而生养万物，偏颇则气乖戾而杀伤万物。《内经》说：阴气平和，阳气固密，精神就能正常；如果阴阳分离决裂，精气就会枯竭。这就是先王教导人们考察阴阳、保养生气的原因。
阳气是一（奇数），阴气是二（偶数），所以偶数属于阴，代表后天的形体；奇数属于阳，代表先天的气。神由气化生，而气本源于天，所以发生我身体的，就是真阳之气；形体由精构成，而精生于气，所以成立我身体的，就是真阴之气。《上古天真论》说：女子十四岁天癸至，男子十六岁天癸至。这不是说明阴在后天生成比较困难吗？《阴阳应象大论》说：人到了四十岁，阴气就自然减半了。这不是说明阴气在前容易衰退凋谢吗？所以人处于全盛状态的时期，只在十六岁之后，直到四十岁之外，前后不过二十多年，形体就开始逐渐衰败了。
阳道常实，阴道常虚，所以朱丹溪引用日月盈亏的道理，提出“阳常有余、阴常不足”的理论，并创立了补阴丸、大补丸等方剂。只可惜他以黄柏、知母作为神丹妙药，导致家家相传、户户使用。却不知道天癸的未至，原本取决于气，而阴阳自半（减半），也取决于气。虽然形体属于阴，但气仍然归属于阳。这是生死的关键，不可不辨明。
阳的意义非常宏大。阴以阳为主导，关系到造化的本源和性命的根本，只有这一点罢了。姑且辨析其中最重要的三个方面：一是形与气，二是寒与热，三是水与火。
关于形与气：阳化气，阴成形，所以形本属阴，而全身温暖的，是阳气；一生活动灵活的，是阳气；五官五脏神明变化莫测的，也是阳气。如果人的灵觉完全消失，身体冷如冰，形体虽然存在，但气已经离去，这是因为阳气脱失在前，而阴留存在后，难道不是阴多于阳吗？这就是形气阴阳的辨别。
关于寒与热：春夏的温暖属于阳，秋冬的寒冷属于阴。在长夏暑热之时，草木昆虫都苦于被煎烤，然而越是被炙烤反而越发繁盛，不热就不旺盛。一旦遇到一夜风霜，就僵死枯萎遍野，这说明热能生物，寒无生机，热不会造成伤害而寒令人畏惧，难道不是寒强于热吗？这就是寒热阴阳的辨别。
关于水火：这是造化的权柄，其形象有四种：日为太阳，火为少阳，水为太阴，月为少阴。这是四象的真实形态。阳中没有太阴，阴中没有太阳，这是阴阳各自专主的表现。日悬挂在天，这是阳中之阳，不就是太阳吗？月悬挂在天，这是阳中之阴，不就是少阴吗？水行于地，这是阴中之阴，不就是太阴吗？火存在于地，这是阴中之阳，不就是少阳吗？这些大义，朱丹溪并不知晓，所以他引用日月盈亏来论证阴阳虚实。况且阴阳的性质，太盛者气刚，所以日不可灭，水不可竭，这是日为火之本，水为月之根；微弱者气柔，所以火有时熄灭，月有时缺憾，这是火为日之余，月为水之余。只有不灭的，才是真火；时而发作时而停止的，难道是元阳吗？所以只有真阳之火，才能生物；而燎原的凡火，只能烧焦物体。天一生水，“天一”指的是天的第一数，一就是阳，如果没有这个一，就止步于六了。所以水能生物，依赖的是这个一；水能化气，依赖的也是这个一。所以春夏之水，土得到它就能生长；秋冬之水，土得到它就不能生长，水也就死了。水之所以生，水之所以行，哪一样不是由阳主导的？这说明水中有阳，并非水本身就是阳。
如果阳气不充盛，那么生机就不广博，更何况是没有阳呢？所以阳只害怕衰弱，阴只害怕过盛，并不是阴能自己过盛，而是阳衰导致了阴盛。凡是万物的生存依靠阳，万物的死亡也依靠阳。并不是阳能让物死，而是阳来则生，阳去则死。试以太阳为例：太阳运行到南陆，对应的时间是冬季，这个时候并非没有太阳，只是距离稍远，便觉得严冬难以抵御，万物凋零。既然这样，天地的和谐，全靠这个太阳；万物的生存，全靠这个太阳。假使没有这个太阳，天地即使广大，也不过是一块寒冷的物质罢了。人是小乾坤，得阳则生，失阳则死。阳气衰弱，就是亡阳的开始。
圣人创作《易经》，首先制定一爻，确立元阳之祖，阐明阳德在坤卦初六爻的元亨之道，提到“履霜坚冰至”，是担心阴气逐渐增长，防止它妨碍化育之功。
《内经》说：大凡阴阳的关键，在于阳气致密然后阴气才能固守。这说的是阴所依赖的，以阳为主。又说：人体的阳气就像天空中的太阳，失去了它的正常位置，就会折损寿命而不显赫，所以天体的运行应当以太阳的光明为准则。可见人体最宝贵的，只有这一息真阳，谁说阳常有余，而想用苦寒的药物，来伐害这阳气，想要保生可以这样做吗？
客人问：想要固护这阳气，有什么办法？回答说：只要知道根本，这就是关键所在，命门就是根本。所谓命门，先天的生命由此接受；后天的自我由此栽培养育。生的门户也就是死的户牖，人的盛衰安危，都系于此。因为它是生气的源头，气强则身强，气衰则生病，这里虽然是极阴之地，但实际上是元阳的宅邸。至于脾胃，是后天水谷的根本，也还算是元阳的儿子罢了。
The substance of Yin and Yang is referred to as Qian (Heaven) and Kun (Earth); their function is referred to as Water and Fire; their transformation is referred to as Form and Qi (Vital Energy). Speaking from the perspective of generation and destruction, Yang generates while Yin destroys; speaking from the perspective of cold and heat, Yang is hot while Yin is cold. Regarding the mechanism of their generation and transformation, Yang acts first and Yin follows later; Yang exerts influence while Yin receives it. In the pre-heaven stage, form is transformed from Qi, which is Yang generating Yin; in the post-heaven stage, Qi is transformed from Form, which is Yin generating Yang. Form is Jing (Essence), and Jing is Water; Shen (Spirit) is Qi, and Qi is Fire. The two Qi of Yin and Yang must not be biased; when balanced, Qi is harmonious and generates living things; when biased, Qi becomes discordant and destroys living things. The Classics state: "When Yin is peaceful and Yang is secure, Spirit and Mind are regulated; when Yin and Yang separate and break apart, Essence and Qi are exhausted." This is how the ancient kings taught people to observe Yin and Yang and preserve vital Qi.
Yang is one (odd number), and Yin is two (even number); therefore, even numbers belong to Yin, representing post-heaven form; odd numbers belong to Yang, representing pre-heaven Qi. Shen arises from the transformation of Qi, and Qi originates from Heaven; thus, what generates my body is the True Yang Qi. Form is composed of Jing, and Jing is generated by Qi; thus, what establishes my body is the True Yin Qi. *Shanggu Tianzhen Lun* (Treatise on the Heavenly Truth of Antiquity) states: "At fourteen years of age, the Tian Gui (menstrual essence) arrives for women; at sixteen years of age, the Tian Gui arrives for men." Does this not indicate that Yin is difficult to complete in post-heaven development? *Yinyang Yingxiang Dalun* (Great Treatise on Yin-Yang Correspondences) states: "When a person reaches forty years of age, their Yin Qi naturally halves." Does this not indicate that Yin declines easily in early stages? Therefore, the period of full vitality lasts only from after sixteen years of age until beyond forty years of age, spanning no more than twenty-plus years, after which the physical form gradually declines.
The path of Yang is often solid/excess, while the path of Yin is often deficient/empty. Thus, Zhu Danxi cited the waxing and waning of the sun and moon to propose the theory that "Yang is often in excess and Yin is often deficient," establishing formulas such as *Buyin Wan* (Nourishing Yin Pill) and *Dabu Wan* (Great Tonifying Pill). It is only regrettable that he regarded Huangbai (Phellodendri Cortex) and Zhimu (Anemarrhenae Rhizoma) as miraculous elixirs, leading to their widespread family transmission and household use. Little did they know that the non-arrival of Tian Gui originally depends on Qi, and the natural halving of Yin also depends on Qi. Although form belongs to Yin, Qi still adheres to Yang. This is the critical juncture of life and death, which must not fail to be distinguished.
The significance of Yang is vast. Yin is governed by Yang; what concerns the origin of creation and the root of life and nature is solely this. Let us distinguish the most important aspects: first, Form and Qi; second, Cold and Heat; third, Water and Fire.
Regarding Form and Qi: Yang transforms into Qi, and Yin forms into structure; thus, form inherently belongs to Yin. However, the warmth throughout the entire body is Yang Qi; the aliveness and activity of life are Yang Qi; the unfathomable spiritual clarity of the five sense organs and five Zang organs is also Yang Qi. If spiritual awareness is completely extinguished and the body becomes cold as ice, although the form remains, the Qi has departed. This occurs because Yang collapses first, leaving Yin behind; is this not Yin exceeding Yang? This is the distinction between Form, Qi, Yin, and Yang.
Regarding Cold and Heat: The warmth of spring and summer is Yang; the cold of autumn and winter is Yin. During the intense heat of late summer, grasses, trees, insects, and animals suffer from being roasted, yet the more they are roasted, the more abundant they become; without heat, there is no flourishing. But upon a single night of wind and frost, they stiffen and wither across the fields. This shows that heat can generate life, while cold lacks vitality; heat causes no harm, but cold is to be feared. Is this not Cold overpowering Heat? This is the distinction between Cold, Heat, Yin, and Yang.
Regarding Water and Fire: These are the powers of creation, manifesting in four images: the Sun is Taiyang (Greater Yang), Fire is Shaoyang (Lesser Yang), Water is Taiyin (Greater Yin), and the Moon is Shaoyin (Lesser Yin). These are the true forms of the Four Images. There is no Taiyin within Yang, and no Taiyang within Yin; this represents the exclusive dominion of Yin and Yang. The Sun shining in the sky is Yang within Yang, is it not Taiyang? The Moon shining in the sky is Yin within Yang, is it not Shaoyin? Water flowing on earth is Yin within Yin, is it not Taiyin? Fire existing on earth is Yang within Yin, is it not Shaoyang? These great principles were unknown to Zhu Danxi, who therefore cited the waxing and waning of the sun and moon to prove the deficiency and excess of Yin and Yang. Furthermore, regarding the nature of Yin and Yang, the greater ones have rigid Qi; thus, the Sun cannot be extinguished, and Water cannot be dried up. The Sun is the root of Fire, and Water is the root of the Moon. The lesser ones have soft Qi; thus, Fire sometimes rests, and the Moon sometimes wanes. Fire is the remnant of the Sun, and the Moon is the remnant of Water. Only that which does not extinguish is True Fire; that which comes and goes intermittently, how could it be Yuan Yang (Primordial Yang)? Therefore, only the fire of True Yang can generate living things, whereas the ordinary fire of prairie fires can only scorch objects. Heaven generates Water with One ("Tian Yi Sheng Shui"). "One" refers to the first number of Heaven; One is Yang. Without One, it would stop at Six. Thus, Water's ability to generate life relies on this One; Water's ability to transform into Qi relies on this One. Therefore, in spring and summer, when Earth obtains Water, things grow; in autumn and winter, when Earth obtains Water, things do not grow or develop, and Water itself dies. Who is the master of Water's generation and movement? Is it not Yang? This indicates that Yang exists within Water, but Water itself is not Yang.
If Yang Qi is not充盈 (abundant), then the scope of vitality is narrow, let alone if there is no Yang at all. Therefore, Yang fears only decline, and Yin fears only excess; it is not that Yin can become excessive on its own, but rather that Yin becomes excessive due to Yang's decline. The birth of all things depends on Yang, and the death of all things also depends on Yang. It is not that Yang kills things; when Yang arrives, there is life; when Yang departs, there is death. Consider the example of the Sun: When the Sun travels through the southern land, corresponding to winter, it is not that there is no Sun at that time, but merely that it is slightly farther away, making severe winter hard to withstand and causing all things to wither. Thus, the harmony of heaven and earth relies solely on this Sun; the survival of all things relies solely on this Sun. If there were no Sun, even if heaven and earth were vast, they would merely be a mass of cold matter. Humans are a small universe; gaining Yang brings life, losing Yang brings death. Decline of Yang is the gradual onset of Wang Yang (Collapse of Yang).
When the Sages created the *I Ching* (Book of Changes), they first established a single line, setting up the Ancestor of Yuan Yang, clarifying the primal prosperity of Yang virtue in the initial six of Kun (Earth). Mentioning "treading on frost, firm ice approaches," they worried about the gradual growth of Yin Qi, guarding against its interference with generative processes.
The *Neijing* (Inner Canon) states: "The key to Yin and Yang is that when Yang is dense, Yin becomes secure." This says that what Yin relies upon is Yang as the master. It also states: "Human Yang Qi is like the sky and the sun; if it loses its proper position, lifespan is shortened and brilliance is obscured. Therefore, the movement of heaven should rely on the brightness of the sun." It is evident that humanity's greatest treasure is but this breath of True Yang. Who says Yang is often in excess, and wishes to use bitter-cold substances to attack this Yang Qi, thinking that preserving life can be achieved this way?
A guest asked: "To consolidate this Yang, what plan should be adopted?" I replied: "Simply knowing the root is the key; this is the Mingmen (Gate of Life)." What is called Mingmen is where we receive our pre-heaven existence; it is where our post-heaven self is nurtured. The gate of life is also the door of death; human flourishing, decline, safety, and danger are all tied to this. Because it is the source of vital Qi, strong Qi leads to strength, and weak Qi leads to illness. Although this is a place of extreme Yin, it is actually the residence of Yuan Yang. As for the Spleen and Stomach, they are the foundation of post-heaven food and water, yet they are merely children of Yuan Yang.