阴阳未判，一气混茫。气合阴阳，则有清浊。清则浮升，浊则沉降，自然之性也。升则为阳，降则为
阴，阴阳异位，两仪分焉。清浊之间，是谓中气。中气者，阴阳升降之枢轴所谓土也。枢轴运动，清
气左旋，升而化火；浊气右转，降而化水；化火则热，化水则寒，方其半升，未成火也，名之曰木；
木之气温，升而不已，积温成热而化火矣；方其半降，未成水也，名之曰金；金之气凉，降而不已
，积凉成寒，而化水矣。水火金木，是名四象
，四象即阴阳之升降，阴阳即中气之浮沉。分而名之，则曰四象。
合而言之，不过阴阳。分而言之，则曰阴阳。合而言之，不过中气所变化耳。四象轮旋，一年而周。阳
升于岁半之前，阴降于岁半之后。阳之半升则为春，全升则为夏，阴之半降则为秋，全降则为冬，春生夏
长，木火之气也，故春温而夏热，秋收冬藏，金水之气也。故秋凉而冬寒，土为专位，寄旺于四季之月
，各十八日，而其司令之时，则在六月之间，土合四象，是谓五行也。
五行之理，有生有克。木生火，火生土，土生金，金生水，
水生木；木克土，土克水，水克火，火克金，金克木；其相生相克，皆以气而不以质也。成质则不能生克矣
。盖天地之位，北寒南热，东温西凉。阳升于东则温气成春，升于南则热气成夏，阴降于西则凉气成秋
，降于北则寒气成冬。春之温，生夏之热，夏之热生秋之凉，秋之凉生冬之寒，冬之寒生春之温。土
为四象之母，实生四象。曰火生土者，以其寄宫在六月火令之后，六月湿盛湿为土气也。其实水火交蒸，
乃生湿气。六月之时，火在土上，水在土下，寒热相逼，是以湿动，湿者水火之中气。土寄位于西南，
南热而西凉，故曰火生土，土生金也。相克者，制其太过也。木性发散，敛之以金气，则木不过散。火
性升炎，伏之以水气，则火不过炎。土性濡湿，疏之以木气，则土不过湿。金性收敛，温之以火气，
则金不过收。水性降润，渗之以土气，则水不过润，皆气化自然之妙也。
阴阳尚未分化时，是一团混沌未分的元气。当元气结合形成阴阳属性时，便产生了清与浊的区别。清气性质轻扬而向上浮升，浊气性质重浊而向下沉降，这是它们自然的本性。上升的属于阳，下降的属于阴，阴阳各有其位，从而分出了两仪（指天地或阴阳两极）。在清与浊之间，存在着中气。中气，是阴阳升降运动的枢纽轴心，也就是五行中的“土”。枢轴运动起来，清气向左旋转，上升而化为火；浊气向右转动，下降而化为水；化火则产生热，化水则产生寒。当气处于半升阶段，尚未完全化为火时，称之为木；木的气性是温热的，如果持续上升，积聚温热最终化为火；当气处于半降阶段，尚未完全化为水时，称之为金；金的气性是清凉的，如果持续下降，积聚凉意最终化为水。水、火、金、木，这被称为四象。四象其实就是阴阳的升降过程，阴阳其实就是中气的浮沉变化。分开来说叫四象，合起来说，不过是阴阳罢了。再分开来说，就是阴阳；合起来说，不过是中气所变化的结果。四象循环运转，一年为一个周期。阳气在半年之前上升，阴气在半年之后下降。阳气的半升对应春季，全升对应夏季；阴气的半降对应秋季，全降对应冬季。春天生发、夏天生长，这是木和火的气性，所以春天温暖、夏天炎热；秋天收敛、冬天闭藏，这是金和水的气性，所以秋天凉爽、冬天寒冷。土占据中央的位置，寄旺于四季的最后一个月（即每季末的十八天），而其真正主事的时间，是在六月之间。土结合了四象，这就称为五行。
五行的道理，包含相生和相克。木生火，火生土，土生金，金生水，水生木；木克土，土克水，水克火，火克金，金克木；它们的相生相克，都是基于“气”的作用，而不是基于“质”的作用。一旦形成了固定的形体（质），就不能再进行生克了。大概天地的位置是北边寒冷、南边炎热，东边温和、西边凉爽。阳气在东边上升，温和之气形成春季；在南边上升，炎热之气形成夏季；阴气在西边下降，凉爽之气形成秋季；在北边下降，寒冷之气形成冬季。春天的温暖，孕育夏天的炎热；夏天的炎热，孕育秋天的凉爽；秋天的凉爽，孕育冬天的寒冷；冬天的寒冷，又孕育春天的温暖。土是四象的母亲，实际上生成了四象。所谓“火生土”，是因为火的宫位在六月火令之后，此时六月湿气旺盛，湿就是土的气性。其实，水火相互交蒸，才产生了湿气。六月的时节，火在土之上，水在土之下，寒热相互逼迫，因此湿气发动，湿是水与火之间的中气。土寄居在西南方位，南方热而西方凉，所以说“火生土，土生金”。所谓的相克，是为了制约过度的气势。木的性质是发散，用金气的收敛来制约它，木就不会过度发散；火的性质是升腾炎上，用水气的潜降来伏制它，火就不会过度炎上；土的性质是湿润黏滞，用木气的疏泄来疏通它，土就不会过度湿润；金的性质是收敛，用火气的温热来温煦它，金就不会过度收敛；水的性质是下降滋润，用土气的渗利来渗透它，水就不会过度滋润。这些都是气化自然产生的奇妙作用。
Before Yin and Yang were distinguished, there was only one undifferentiated, chaotic Qi (vital energy). When Qi combined to form Yin and Yang, clear and turbid qualities emerged. The clear quality floats and rises naturally, while the turbid quality sinks and descends; this is their inherent nature. Rising constitutes Yang, descending constitutes Yin; with Yin and Yang occupying different positions, the Two Modes (Liangyi, referring to Heaven and Earth or the two poles of Yin and Yang) are divided. Between the clear and the turbid lies the Middle Qi (Zhong Qi, central energy governing transformation). The Middle Qi serves as the pivot axis for the ascent and descent of Yin and Yang, which corresponds to the element Earth (Tu). As the pivot moves, the clear Qi rotates to the left, ascending and transforming into Fire (Huo); the turbid Qi rotates to the right, descending and transforming into Water (Shui). Transformation into Fire generates Heat (Re), and transformation into Water generates Cold (Han). When the Qi is halfway up but has not yet fully transformed into Fire, it is named Wood (Mu); the Qi of Wood is warm, and if it continues to ascend, accumulated warmth transforms into Fire. When the Qi is halfway down but has not yet fully transformed into Water, it is named Metal (Jin); the Qi of Metal is cool, and if it continues to descend, accumulated coolness transforms into Water. Water, Fire, Metal, and Wood are called the Four Symbols (Si Xiang). The Four Symbols are essentially the ascent and descent of Yin and Yang, and Yin and Yang are essentially the floating and sinking of the Middle Qi. Separately named, they are called the Four Symbols; collectively speaking, they are merely Yin and Yang. Separately discussed, they are Yin and Yang; collectively discussed, they are merely changes arising from the Middle Qi. The Four Symbols rotate in a cycle, completing one revolution per year. Yang ascends in the first half of the year, and Yin descends in the second half. Half-ascent of Yang corresponds to Spring (Chun), full ascent corresponds to Summer (Xia); half-descent of Yin corresponds to Autumn (Qiu), full descent corresponds to Winter (Dong). Spring generation and Summer growth are the Qi of Wood and Fire, hence Spring is warm and Summer is hot; Autumn harvesting and Winter storing are the Qi of Metal and Water, hence Autumn is cool and Winter is cold. Earth occupies the central position and thrives during the last month of each season (eighteen days each), but its time of command lies within the sixth month. Earth combines with the Four Symbols, which is termed the Five Elements (Wu Xing).
The principle of the Five Elements involves mutual generation (Sheng) and mutual restriction (Ke). Wood generates Fire, Fire generates Earth, Earth generates Metal, Metal generates Water, and Water generates Wood; Wood restricts Earth, Earth restricts Water, Water restricts Fire, Fire restricts Metal, and Metal restricts Wood; their mutual generation and restriction operate through Qi rather than substance (Zhi). Once fixed substances are formed, generation and restriction can no longer occur. Generally, the positions of Heaven and Earth are cold in the North and hot in the South, warm in the East and cool in the West. Yang ascending in the East produces warm Qi forming Spring; ascending in the South produces hot Qi forming Summer; Yin descending in the West produces cool Qi forming Autumn; descending in the North produces cold Qi forming Winter. The warmth of Spring generates the heat of Summer; the heat of Summer generates the coolness of Autumn; the coolness of Autumn generates the cold of Winter; the cold of Winter generates the warmth of Spring. Earth is the mother of the Four Symbols and essentially generates them. The statement "Fire generates Earth" exists because Fire's palace is located after the Fire command of the sixth month, when dampness is abundant; dampness is the Qi of Earth. In reality, the intermingling steaming of Water and Fire generates dampness. During the sixth month, Fire is above Earth and Water is below Earth; cold and heat press against each other, causing dampness to move. Dampness is the Middle Qi between Water and Fire. Earth resides in the Southwest position; the South is hot and the West is cool, hence it is said that "Fire generates Earth, and Earth generates Metal." Mutual restriction refers to controlling excess. The nature of Wood is dispersing; restricting it with Metal Qi prevents excessive dispersion. The nature of Fire is rising and flaming; subduing it with Water Qi prevents excessive flaming. The nature of Earth is moist and sticky; venting it with Wood Qi prevents excessive moisture. The nature of Metal is contracting; warming it with Fire Qi prevents excessive contraction. The nature of Water is descending and moistening; infiltrating it with Earth Qi prevents excessive moisture. These are all the wondrous effects of natural Qi transformation.