The Meaning of the Order and Position of the Eight Trigrams

故立卦，而萬物萬事皆自卦中出；天地尚不外是，況其下者乎？故卦者卦也，言以一而卦眾也。懸則以測物，謂之卦；卦立，則物物事事皆得依則以測之，故能周知無窮。八卦之序，乾一、兌二、離三、震四、巽五、坎六、艮七、坤八；自乾至震，自巽至坤，分為左右，而仍成圓形，以二氣之往來相續，循環無已也。乾坤對列，六子成行，以明陰陽之有所屬，而升降之有次也。

Therefore, once a hexagram is established, all things in the universe emerge from it. Even heaven and earth do not go beyond this scope, let alone the things beneath heaven and earth. Therefore, the term "hexagram" refers precisely to the meaning of encompassing a multitude of things with a single hexagram. To suspend the principles and measure things by them is called a hexagram. Once a hexagram is established, all things can be measured according to this principle, thus enabling the comprehensive understanding of infinite matters. The order of the eight trigrams is: Qian (Heaven) one, Dui (Lake) two, Li (Fire) three, Zhen (Thunder) four, Xun (Wind) five, Kan (Water) six, Gen (Mountain) seven, Kun (Earth) eight. Counting from Qian to Zhen forms one sequence, and from Xun to Kun forms another sequence, dividing them into left and right sides, yet together they form a circle. This is because the dual forces of yin and yang continuously flow and cycle without end. Qian and Kun are paired opposite each other, and the six subsidiary trigrams follow in sequence, illustrating how yin and yang each have their proper place and order of ascent and descent.

故一二三四之序，乃位次也；必求於象之變化，始見氣之進退。如自下而上，則震者坤所變；自上而下，則巽者乾所化，其序不同，亦相當也。蓋陰陽二者，往來不已，初非泥於一地也；升降有時，初非限於一日也。故時位不同序，升降往來不同道，消長進退不同途，各以所宜而自至焉。卦象亦如之，故以兌次乾，言兌之上既復，即歸於乾；

Therefore, the numbers one, two, three, and four refer to the order of positions; one can only understand the movement of qi by observing the changes in the hexagram. For example, looking from the bottom up, "Zhen" comes from "Kun"; looking from the top down, "Xun" comes from "Qian": the direction of the numbers differs, yet their positions remain corresponding. Since yin and yang qi continuously move and change, they do not remain fixed in one place; their rising and falling occur at specific times and are not limited to a single day. Therefore, time and position do not share the same order, rising and falling do not follow the same path, and growth and decline do not proceed along the same route; each follows its own appropriate way to reach its destination. Hexagrams are the same, so "Dui" is placed after "Qian," meaning that once the top line of "Dui" returns to its original position, it reverts to "Qian."

以巽隨乾，言乾之初初變，即成為巽。一來一往，一進一退，各有序也。由兌溯離，可見其升之道；由巽推坎，可見其去之途，其相次亦有定也。坤之與震艮亦然，不可泥一二之序，而執於一偏；必通各象之形，而尋其所至。此八卦位序所賅之義，實至精深也。

The trigram Xun follows Qian immediately, meaning that the first line of Qian changes to become Xun. One goes and comes, advances and retreats, each with its own order. From Dui tracing back to Li, we can see the path of rising yang energy; from Xun extending to Kan, we can see the path of retreating yang energy: their sequence before and after is equally definite. The positions of Kun, Zhen, and Gen are also like this; one should not be rigid about the numbers one, two, etc., and fixate on one side. Instead, one must observe the forms of the images of all the trigrams to find out where they have actually arrived. The principles contained in the positions of the Eight Trigrams are indeed extremely profound.

陽之進者，為陰之退；陰之長者，為陽之消，此易見者也。皆定於三畫，故有多必有少，有減必有加，其象所具，則數之所計也。故坤納艮之陽而變震，震之初爻，即乾之下；乾氣初見，坤氣即潛；此震卦之象，示由靜初動，由陰生陽之機。其象既明，其氣亦昭；觀其所變，即得其所示之義矣！不獨震也，餘卦皆然。

When yang advances, yin retreats; when yin grows, yang diminishes. This is easy to observe. All of this depends on the arrangement of the three lines. Where there is more, there must be less; where there is reduction, there must be addition. What is contained in the hexagram is precisely what is calculated by numbers. Therefore, the yang line that is incorporated into the hexagram of Kūn becomes the hexagram of Zhèn. The first line of Zhèn is exactly the lower line of Qián. As the yang energy of Qián begins to appear, the yin energy of Kūn retreats secretly. This is the image of Zhèn, which shows the moment when stillness turns into movement and yin gives rise to yang. Once the image is clear, the energy becomes evident. By observing where the change occurs, one gains the meaning that the hexagram aims to convey. Not only does Zhèn follow this pattern, but all other hexagrams do as well.

故來往有途，進退有道；以成環行，永無斷絕。此始彼終，非真始終也，為便於紀錄，謂之始終耳。如春去夏來，秋往冬至，此一歲之始終，為紀歲也；實則冬去春復來，日月何嘗有所始終哉？彼八卦之交遞亦猶是也。故泥其跡則不達，通其意則皆知；氣行無垠，數至有紀；必旁通各象而會歸之，方得聖人立卦之心，與河洛圖書相合之義耳。

So coming and going have their own paths, advancing and retreating have their own principles, thus forming a circular movement that never ceases. This side is considered the beginning, that side the end, but there is no real beginning or end. It is only for convenience of record that they are called beginning and end. For example, spring goes and summer comes, autumn passes and winter arrives; this is the beginning and end of a year, established for the purpose of recording years. In reality, after winter comes spring again, and the sun and moon never truly have a beginning or an end. The alternation of the Eight Trigrams is also like this. Therefore, clinging to its surface traces will not lead to understanding, but grasping its meaning will bring clarity. The movement of qi has no boundaries, but the numbers have their order and structure. Only by comprehending the images of all the trigrams and integrating them can one understand the original intention of the sage in establishing the trigrams, as well as the connection between them and the Yellow River Chart and the Luo Writing.

夫卦之用以測物，必自物之既生始；物物事事所自生成者三，天地人是也。故卦之爻三，既仿河圖中之三五也。然生成必自二氣之合化，孤陰獨陽不克生化也；必合陰陽，而後生成之功始見；必列陰陽，而後事物之情始明。此三爻之卦必重，重而後竟其用也，亦即河圖、洛書四方之數，以一陰一陽交合成象之義。故卦之體三爻，而成用，則六爻也。

The use of hexagrams is to measure and understand things, and measurement must begin after things have already come into being. All the factors that enable things to be generated are three, namely heaven, earth, and humanity. Therefore, hexagrams have three lines, which is exactly imitating the number 'three' and 'five' in the Yellow River Chart. However, generation must come from the combination of yin and yang energies. A single yin or a single yang cannot generate by themselves; it is only when yin and yang meet and interact that generation occurs. It is only when yin and yang are combined that the forms of things become clear. Therefore, a three-line hexagram must be overlapped, and only after overlapping can its full function be exhausted. This is also the meaning of the Yellow River Chart and the Luo Writing, where the numbers of the four directions are formed by the mutual combination of one yin and one yang. Therefore, the 'body' of a hexagram is three lines, but to achieve its 'function', it must be six lines.

天有陰陽，地有柔剛，人有仁義；皆二氣相間，以生成事物，而見其情性者也，名之日道，言物物事事必由者也。天地人之合，而二氣行止於其間，故卦象以六爻分象之，而變化亦因之生矣！六爻之卦所自成者以此。原夫天下之物事，莫不以陰陽之從違，為有無生化之本；陰者求陽，陽者求陰，合而有得，生化無盡，則前之孤獨者，至此必偶；而前之三爻者，至此必重。此重卦之立，亦本乎生化自然所至者也。

Heaven has yin and yang, earth has softness and firmness, and humans have benevolence and righteousness; these are all manifestations of the intermingling of yin and yang energies, used to generate things and reveal their nature. This is called "the Dao," referring to the principle by which all things must follow. Heaven, earth, and humanity converge, and the two energies operate within them, so the trigrams use six lines to represent them, and change arises accordingly. The formation of hexagrams with six lines is due to this reason. Investigating all things in the world, none exists without relying on the mutual following or opposing of yin and yang as the fundamental basis for existence and transformation: yin requires yang, and yang requires yin, combining to gain from each other, thus generation and transformation have no end. Therefore, what was originally single becomes paired, and what was originally three lines becomes doubled. Hence, the formation of compound hexagrams is also based on the natural tendency of generation and transformation.

如乾之三爻也，無所謂生成，故無所謂物事，不過以象天之元氣而已。若推其生成，象其物事，則必加其所行止之象，而仿其氣之動靜，名其數之奇偶，以盡其生化之用，則三爻之乾，即重為六爻矣！動靜之所別，行止之所殊，而後可記可名，不復渾沌；而氣之所至，亦悠然見之於數矣！

For instance, when "Qian" (Heaven) consists of only three lines, it cannot be said to have generation or to represent anything, but merely symbolizes the primordial qi of Heaven. If we wish to investigate its generation and to manifest its representation, we must add the images of its movement and stillness, imitate the movement and stillness of its qi, and indicate the odd and even numbers to exhaust its function of generation and transformation. In this way, the three lines of "Qian" become six lines. Only when movement and stillness are distinguished, and movement and rest differ, can it be recorded and named, no longer a confused whole; and the extent to which the qi reaches can then be clearly manifested through numbers.

如乾卦既為六爻，已由陽而生陰，奇而成偶；前之三九為奇者，今已六九為偶；奇之為陽者，今已偶之為陰矣！此孚於二氣之妙用，生化之大則，莫之為而為，莫之致而至者也。蓋陽動必生陰，體陽者必用陰；乾雖純陽之氣，若既動矣，亦當生陰；既用矣，必當有陰，不必其變也。以三爻之重，逐換奇為偶，非爻之變，其數之自易也。

For example, the hexagram "Qian" (Heaven) has already become a hexagram of six lines. It has already generated yin from yang, and transformed from odd to even: previously, three lines of nine multiplied together gave twenty-seven, an odd number; now, six lines of nine multiplied together give fifty-four, an even number. Previously, because it was odd, it belonged to yang; now, because it is even, it belongs to yin. This conforms to the subtle workings of yin and yang and the great principle of generation and transformation. It is "without anyone doing it yet it is accomplished, without anyone prompting it yet it is achieved." Because yang once moves, it must generate yin; something that belongs to yang must use yin. Although "Qian" is purely yang, once it moves, it should generate yin; once it is used, it must contain yin, without needing the line markings to actually change. Simply doubling the three lines into six lines sequentially changes odd into even: this is not the lines changing, but the number itself changing.

乾卦如是，餘卦亦然，故體用不同，動靜各異；因其異，而氣乃見，數乃明；生成之功，乃得而言；事物之類，乃得而辨，則六爻重卦者，實易道之本，而言易者所必知者也。重卦之爻六，因而變化以成六十四卦，即八自乘數也；六爻之變為三百八十四爻，因而變化以成四千九十六，即六十四之乘數，皆自變出。故六爻重卦，為極卦之變，而窮象之用也。

The hexagram Qian is like this, and all other hexagrams are the same. Therefore, the essence and function differ, movement and stillness vary; precisely because of these differences, qi becomes apparent and numbers become clear; the process of generation has something to say, and the classification of things has a method to follow. Thus, the hexagram with six lines is indeed the fundamental principle of the Way of the Book of Changes, something essential for those who study the Book of Changes. The hexagram has six lines, thus generating the sixty-four hexagrams through change, which is the square of eight; the six lines each change, forming three thousand eight hundred and forty lines, thus generating four thousand and nine十六, which is the square of sixty-four—these are all derived from change. Therefore, the hexagram with six lines pushes the change of the hexagram to its extreme and exhausts the function of the images to the very end.

伏羲之初創時，由八卦之三爻，易為六爻，八卦之用以見；由六爻之變，成六十四卦，而八卦之變以明；若再推之，則變者愈多，為用愈廣，其所以測事物者，亦無盡矣！故卦之體止於八，而變則無盡，則由於六爻之重卦也。其所仿者，河圖之數，易為洛書；二氣分合，化成萬類，皆以數之變，而象以成，類以眾也。易卦之象，三爻者，陰陽自純，而六爻則交錯矣！

Fuxi originally created the Eight Trigrams, and changed the three lines of each trigram into six lines, thus making the function of the Eight Trigrams evident. Then, by the movement of the six lines, the sixty-four hexagrams were formed, and the changes of the Eight Trigrams became clear. If we continue to derive further, the changes would become even more numerous, and their applications would be even broader. Using them to measure things would have no end. Therefore, the "body" of the hexagrams stops at eight, but their "changes" have no end, because of the repeated hexagrams with six lines. It imitates the transformation of numbers from the Yellow River Chart to the Luo Writing: yin and yang energies have both separation and union, giving rise to myriad things. This is all due to the movement of numbers, which allows images to be formed and categories to become numerous. In terms of the images of the Book of Changes, the three-line trigrams still have pure yin and pure yang, but in the six-line hexagrams, they have become intermingled and mixed.

三爻者，生化未見；而六爻，則分明矣！六爻之卦，繫後天之象，蓋氣已動，而形亦成，數已繁，而用亦廣，非復單純之象可比；則觀象以辨物，徵數以卜事者，必於爻求之，且必於重卦之爻求之也。三爻之象天地人也，為數甚簡；六爻則天在上，地在下，人居中，各得二爻，其數已繁。由下而上，地居其始；由上而下，天處其顛；人在中央，得二氣之和。

The third line of a trigram, the trigram itself, has not yet shown its transformation; but in the case of a hexagram, the lines are clearly visible. A hexagram belongs to the Later Heaven configuration, because at this point the energy has already begun to move, the form has already been established, the numbers have become numerous, and the application has become extensive. It is no longer comparable to a simple image. Therefore, to observe the images in order to distinguish things and to use numbers in order to predict events, one must look at the lines, and specifically at the lines of the compound hexagram. A trigram represents heaven, earth, and humanity, with a simple number of lines; but a hexagram has heaven above, earth below, and humanity in the middle, with each of the three elements occupying two lines, making the number of lines more complex. Looking from below, earth is at the beginning; looking from above, heaven is at the top; humanity is in the center, receiving the harmonious influence of yin and yang energies.

故爻六而氣仍二，天氣上行，地氣下降；一卦之例，正如八卦之方位圖。故乾氣自初至五，為乾之正位，即九五也；坤氣自上至二，為坤之正位，則六二也。陽者陰用，陰者陽用，陰陽交用者也。

Therefore, although there are six lines, the energy remains just two streams: the heavenly energy ascends upward, and the earthly energy descends downward; the structure within one trigram is exactly like the directional diagram of the eight trigrams. Thus, the energy of Qian ascends from the first line to the fifth line, which is Qian's central position, known as 'nine five'; the energy of Kun descends from the top line to the second line, which is Kun's central position, known as 'six two'. Yang is used with Yin, and Yin is used with Yang; Yin and Yang are interdependent in their use.

故天氣下行，而地氣上達，人在其中也；卦之有爻，以紀數也；爻之有象，以明氣也；重卦之爻，二氣或備；六爻之用，八卦俱全；陽奇陰偶，天往地來；故在下為初，在未為上；初以明時之始，上以紀位之高；皆氣之所至、所行、所進、所退也。故卦爻六，而所象甚多；類雖三，而所用無盡也。

Therefore, the heavenly qi descends, and the earthly qi ascends, with humans in the middle. The lines in the hexagrams are used to record numbers; the lines have images to explain qi. The lines in the compound hexagrams contain both yin and yang qi in general; the functions of the six lines include all the meanings of the eight trigrams. Yang is paired with odd numbers, and yin with even numbers; the heavenly qi descends, and the earthly qi ascends. Therefore, the line at the very bottom is called "Chu" (Initial), and the line at the very top is called "Shang" (Upper): "Chu" indicates the beginning of time, and "Shang" records the lofty position. These all show the movement, arrival, advancement, and retreat of qi. Thus, although there are only six lines in a hexagram, they can represent a great variety of things; although the three principles (Heaven, Earth, and Humanity) are only three categories, their functions are endless.

文王八卦，世所稱為後天卦象者，即今本易經所傳，以別於連山歸藏，故曰周易。其八卦方位次序，與伏羲者不同，易傳帝出乎震一節，即指明其位次也。其位次之定，亦由於太極圖及洛書之象，合伏羲卦而互闡其用也。蓋伏羲之卦，位次依於河圖；文王之卦，位次仿於洛書；一體一用，一天一人，其異者正其變化之跡，其變者正其自然之象，初非文王故異之而變之也。

King Wen's eight trigrams, commonly referred to as the Later Heaven trigrams, are the system found in the currently transmitted version of the Classic of Changes. This system is distinguished from the Lianshan and Guicang, hence it is called the Zhou Yi. The arrangement and order of the trigrams in the Zhou Yi differ from those in Fuxi's system. The passage "The Emperor arises from Zhen" in the Sayings on the Trigrams section of the Commentary on the Changes explains precisely the positional sequence of the Zhou Yi trigrams. The determination of these positions is based on the Taiji diagram and the image of the Luo Book, combined with Fuxi's trigrams to elucidate their functions. Generally speaking, Fuxi's trigrams are based on the He Tu, while King Wen's trigrams follow the pattern of the Luo Book: one belongs to "body" and the other to "function"; one emphasizes heaven, the other emphasizes humanity. The differences between the two are the traces of transformation; their changes are the expressions of nature, not because King Wen deliberately sought to differ from Fuxi and made intentional alterations.

文王之卦，原伏羲所制，八卦及六十四卦，六爻及三百八十四爻，皆無異也，其所異者，方位次序而已。因方位之異，而見主客之殊；因次序之異，而見生化之別；無非就天人之間，事物之內，盡其情狀，推其始終，以象之於卦，而足為推測之用耳。故位次之不同，乃卦之自變，文王不過因而演之，以成易耳。他如連山歸藏，亦如此例，各以不同而征其變，以變而成其易而已。

King Wen's hexagrams were originally established by Fuxi: the eight trigrams and the sixty-four hexagrams, the six lines and the three hundred and eighty-four lines, are all the same. The difference lies only in their positions and order. Because of different positions, the distinction between the main and the guest becomes apparent; because of different order, the difference between origin and transformation is shown. This is simply a complete description of the situations between heaven and humanity, and within things and events, making clear their beginning and end, and then taking the form of hexagrams so that they may be used for divination. Therefore, the difference in positions is actually the change of the hexagram itself, and King Wen merely followed this change and explained it, thus composing the Book of Changes. Other works such as the Lianshan and Guicang are similar examples, each using different arrangements to verify their changes, relying on this 'change' to become their own respective Books of Changes.

夫易固取變易為旨者，則推異致變，亦伏羲易之所有。而人事變易無窮，一易之象，無以盡之，則雖屢變屢異，既為易道所包者，自可順其然，而推衍其新。蓋後天之事物日繁，氣數日變，而易亦象之，以成後天之卦也。故卦之方位，非前之地位；次序非前之交代；其各類以殊，道路以別。觀文王之制，即可見後天與先天之不同也。夫先天八卦以乾坤居上下，而後天則易以離坎；先天以日月列東西，而後天則易以震兌；而乾坤反在其則，與巽艮同處於隅者、何也？

The Book of Changes originally focuses on "change," so seeking differences and causing change is something inherent in Fuxi's Book of Changes. Since human affairs are ever-changing and endless, a single set of hexagrams in the Book of Changes cannot fully express all these changes. Therefore, even though changes occur repeatedly and differences arise continuously, as long as they remain within the scope of the principles of the Book of Changes, one can naturally derive new forms by following the natural course. As later phenomena become increasingly complex and the transformations of qi become more frequent, the Book of Changes also takes on new symbolic forms, thus forming the later hexagrams. Therefore, the positions of the hexagrams are no longer as they were before, and their order is no longer the same as before; their categories have changed, and their paths have diverged. By looking at King Wen's arrangement, one can clearly see the differences between the later and earlier hexagrams. In the earlier hexagrams, Heaven and Earth occupy the top and bottom positions, but in the later hexagrams, they are replaced by Fire and Water. In the earlier hexagrams, the Sun and Moon are placed in the east and west, but in the later hexagrams, they are replaced by Thunder and Lake. Heaven and Earth even retreat to the corners, alongside Xun and Gen—why is this so?

蓋即後天之氣數然耳。後天者，本生生不息之例，為變化不居之規；不息則位無定方，行無定所；不居則氣有消長，數有盈虛，與先天者自異其趣矣。以先天之氣，變為後天事物，則體用自殊。如後天之二氣，以水火為主，水火代乾坤大用，為五行之首，為陰陽主器，司萬物之生，故坎離二卦為上下正位，示後天生化之本源，如先天之乾坤也。且先天之氣純，一交而分後天，則相錯以行，相和以化，不可劃為二也。

This is precisely due to the later heaven's qi numbers. The so-called "later heaven" is essentially the common principle of continuous generation and the ever-changing rules: because it is unceasing, there is no fixed direction or place for its movement; because it is ever-changing, the qi has both decline and growth, and the numbers have both fullness and emptiness, differing from the natural principles of the earlier heaven. When the qi of the earlier heaven transforms into the things of the later heaven, the nature and function naturally differ. For example, the yin and yang qi of the later heaven are mainly water and fire: water and fire take the place of heaven and earth to perform their great functions, occupying the first place among the five phases, serving as the main tools of yin and yang, governing the growth of all things. Therefore, the two trigrams "Kan" (Water) and "Li" (Fire) occupy the upper and lower central positions, showing the origin of later heaven's generation and transformation, just as the trigrams "Qian" (Heaven) and "Kun" (Earth) do in the earlier heaven. Moreover, the qi of the earlier heaven is pure and unified. Once it is differentiated through interaction to become the things of the later heaven, it runs in a mixed manner and harmonizes in generation and transformation, and can no longer be clearly divided into two separate parts.

如水火為陰陽合體，水以陽合於陰，火以陰藏於陽，其成固非純。而水以體陽用陰，故坎屬陽而在下；火以體陰用陽，故離屬陰而居上；其行固交錯以推演之也。故連歸之後，文王又重演之，得文王之易，而伏羲之卦象更明。以用能昭體，人能合天，其義一貫，其道互證，而其象數變化，尤能全始終。

For instance, water and fire are both composite entities formed by the union of yin and yang: water is formed by yang entering into yin, while fire is formed by yin being concealed within yang. Their composition is inherently not pure. Water has a yang nature in its substance but a yin nature in its function, so the trigram "Kan" (Water) is classified under yang but is placed below; fire has a yin nature in its substance but a yang nature in its function, so the trigram "Li" (Fire) is classified under yin but is placed above. Their operation is inherently interwoven and interdependent. Therefore, after the books of "Lianshan" and "Guicang", King Wen reinterpreted them and developed the "Yi" (Book of Changes) of King Wen. As a result, the hexagrams of Fuxi became even clearer. This is using function to reveal essence, using human affairs to connect with heavenly principles. The meanings are consistent, and the reasoning mutually supports each other. The changes in images and numbers are especially able to connect from beginning to end.

一本末，足以探天下之繁賾，極事物之常變者也。故以先天名伏羲之易，後天名文王之易，示雖有異，不過先後之分。其如一人亦有先後天，事物皆然，則先後天之易，猶一易也，何可異視之耶？文王卦位次之變自伏羲卦者，由於先天之氣數，因動靜往來而生變化，如河圖之象，因五行之交代而生變化也。故河圖易而洛書成，先天卦易而後天卦見，其例然也。

Unifying the beginning and the end is sufficient to explore the complexity and depth of the world, and to exhaust the normal and abnormal states of things. Therefore, the Book of Changes attributed to Fuxi is called Earlier Heaven, and the Book of Changes attributed to King Wen is called Later Heaven, indicating that although they are different, they are merely a matter of earlier and later. This is like a person having both an Earlier Heaven and a Later Heaven; all things are the same. Thus, the Earlier Heaven Book of Changes and the Later Heaven Book of Changes are actually the same Book of Changes; how can they be regarded as two separate things? The reason why King Wen's arrangement of the hexagrams changed from Fuxi's is because the qi of the Earlier Heaven changes due to movement and stillness, coming and going. It is similar to the image of the Yellow River Chart changing into the Luo Writing due to the alternation of the Five Phases. Therefore, the Yellow River Chart changes into the Luo Writing, and the Earlier Heaven hexagram changes into the Later Heaven hexagram, following the same pattern.

先天之象，陰陽始判，天地始位，氣動而升，形定而降。乾坤定位於上下，日月交行於東西，陽由地升而為震，陰自上降而成風；澤則近天，以示陽之近極；艮則近地，以明陰之將盈；其位定而次明也。定則不變，明則不化；不變則窮，不化則滅，而天地將息，事物何生？此先天之氣數，必由窮而變，明而通，生而繼滅，化而繼盡，以太極之運，本不息也。

The image of the Earlier Heaven shows the stage when yin and yang were just beginning to differentiate and heaven and earth were just beginning to be established: when the qi moves, it rises; when the form is fixed, it descends. Heaven and Earth are positioned at the top and bottom, while the sun and moon move across east and west. Yang qi rises from the earth, becoming "Zhen" (Thunder), and yin qi descends from above, becoming wind, which is "Xun" (Wind). The marsh is near heaven, showing that yang has approached its extreme; "Gen" (Mountain) is near the earth, indicating that yin is about to be full. When positions are fixed, the order becomes clear. However, once fixed, there is no change; once clear, there is no generation. No change leads to exhaustion, no generation leads to extinction. If heaven and earth were to stop, where would things come from? Therefore, the qi of the Earlier Heaven must necessarily arise from exhaustion to bring about change, from clarity to seek communication, and from extinction to bring about life, and from exhaustion to bring about transformation—because the movement of the Taiji never ceases.

天地之氣，原貴生也，故不息以行其位，而性使然也。水性流下，故就地；火性炎上，故親天；故天火為同人，水地為比。且其致用，則水以體陽宜上升，火以體陰宜下濟，如天道尊而下，地道卑而上，故水火為既濟，火水為未濟，皆以其所得於二氣者交錯，所行於天地者同化，而足以為萬物生化之本，代乾坤上下之用也。此後天八卦方位，皆定於坎離，不復同於先天矣。夫坎離既主後天之位，為全易之宗，則猶先天之乾坤，為諸卦之主，已無疑矣。

The vital energy of heaven and earth naturally values "generation" as its essence, thus continuously moving in their respective directions, which is inherent to their nature. Water flows downward, so it tends toward the earth; fire ascends, so it adheres to heaven. Therefore, when heaven is above and fire below, it forms the hexagram of "Union"; when water is above and earth below, it forms the hexagram of "Following." Regarding their initiating transmission, water, though belonging to yang, should rise, and fire, though belonging to yin, should descend. Just as the heavenly way, though exalted, gives downward, and the earthly way, though humble, receives upward; thus, when water is above and fire below, it forms the hexagram of "Already Completed," and when fire is above and water below, it forms the hexagram of "Not Yet Completed." This is because they receive exactly the right intermingling from the two primordial energies, yin and yang, and their movement in the world is exactly harmonized, thus becoming the fundamental force for the generation of all things, taking the place of heaven and earth in their roles of above and below. This is why the later heaven trigrams are all determined by kan and li, not the same as in the earlier heaven. Since kan and li now govern the later heaven directions and become the main trigrams of the entire Book of Changes, they are like the earlier heaven's qian and kun, the rulers of all hexagrams, which is without doubt.

而先天日月之象、東西之行，今既以坎離象水火而代天地，則必易以震兌，而指日月之升降，明陰陽之道路。在先天以天言，則為東西；在後天以人言，則為左右。先天之日月升降，即後天之晝夜往來。故震在東方，示日所生為陽所始；兌居西方，示月所出為陰所行。在一日為旦夕之分，在一年為春秋之別。

In the Earlier Heaven arrangement, the images of the sun and moon are represented by the trigrams Li (Fire) and Kan (Water), positioned east and west respectively, symbolizing their rising and setting, traversing the east-west path. Now, in the Later Heaven arrangement, the trigrams Kan (Water) and Li (Fire) are used to symbolize water and fire, taking the positions of Heaven and Earth instead. The original positions indicating the sun and moon in the east and west are thus left vacant, and the trigrams Zhen (Thunder) and Dui (Lake) are used instead to indicate the rising and setting of the sun and moon, thereby marking the channels of yin and yang movement. In the Earlier Heaven arrangement, the discussion is from the perspective of Heaven, hence the terms east and west. In the Later Heaven arrangement, the discussion is from the human perspective, hence the terms left and right. The rising and setting of the sun and moon in the Earlier Heaven arrangement correspond to the alternation of day and night in the Later Heaven arrangement. Therefore, the trigram Zhen is placed in the east, indicating the birth of the sun, which is the beginning of yang energy; the trigram Dui is placed in the west, indicating the emergence of the moon, which is the beginning of yin energy. This distinction between rising and setting divides a day into morning and evening, and a year into spring and autumn.

而以五行言之，則震為東方之木，兌屬西方之金。木生火而相親，則陽升之道；金生水而相近，則陰降之途。既以水火主生化之中樞，自當以金木司生化之相位。此震兌在後天居左右之地，代日月之明，本陰陽升降之機，為天地生殺之宰。而與先天之象，以變而殊、化而易者，正由後天五行之氣、萬物之生化，自然而然，自至而成，其方位次序遂依此而見矣。

If we consider the Five Phases, "Zhen" (Shock) belongs to the Eastern Wood, and "Dui" (Lei) belongs to the Western Metal. Wood can generate fire, which is closely related to fire, and this is the path of ascending yang energy; Metal can generate water, which is close to water, and this is the path of descending yin energy. Since the Later Heaven has already used the trigrams of water and fire as the central elements of generation and transformation, the positions that support them naturally should be entrusted to the phases of Metal and Wood. This is why "Zhen" and "Dui" occupy the left and right positions in the Later Heaven trigram arrangement: they take the place of the sun and moon to illuminate, and they themselves are the pivot of yin and yang rising and falling, thus becoming the masters of growth and decline in the universe. As for why the Later Heaven image differs from the Earlier Heaven and must be changed, it is because the Later Heaven operates through the energies of the Five Phases, within which all things grow, develop, and mature naturally, and thus the directions and order become evident.

河圖之易為洛書，由五行化為九宮，此自然變化所至者也。先天卦之變後天亦如是。以先天之卦，分陰分陽，統於乾坤；而後天之卦，則陰陽交錯，或老或少，升降往來，或多或少，而統於四正，即坎離震兌也。四卦應四象，而推演之，以加於四隅，象氣之多寡、數之進退，而仍附於四正。以其數不止四，卦則演為八，猶陰陽之復分陰陽也。故八卦出於四象。

The transformation of the Yellow River Chart into the Luo Writing is due to the transformation of the Five Phases numbers into the numbers of the Nine Palaces, which is a result that naturally occurs. The change from the Earlier Heaven trigram positions to the Later Heaven trigram positions follows the same principle. In the Earlier Heaven trigrams, yin and yang are completely separated, and all are subordinated to the trigrams Qian and Kun. In the Later Heaven trigrams, yin and yang intermingle; some are old and some are young, with the movement of qi having more or less. All are subordinated to the four cardinal directions, which are the trigrams Kan, Li, Zhen, and Dui. These four trigrams correspond to the Four Symbols. From them, further trigrams are added to the four corners to represent the quantity of qi and the advance and retreat of numbers. These corner trigrams still depend on the four cardinal trigrams. Since the numbers to be expressed are not limited to four, the trigrams develop from four to eight, just as yin and yang are further divided into yin and yang. Therefore, the Eight Trigrams arise from the Four Symbols.

而四隅之卦，本於四正也。四隅之卦乾坤巽艮，在先天為正位，與老陰少陽，所象重要；而在後天，則繫坎離震兌之所分化，以明氣之往來、數之大小而已，故反置於隅位，不似先天之重要矣。蓋天地生化有主宰，氣數有權衡，當位者貴，逢時者宜。坎離震兌，位當時逢，其綱領全易，如一歲之四時、天下之四方，為拄持全體者也。而乾坤巽艮，則其節目，附庸於四正者，故處於隅位，而當於閒時，其取象自異於先天也。

The four corner trigrams are actually derived from the four main trigrams. The trigrams Qian, Kun, Xun, and Gen, which later occupy the four corners, originally held central positions in the Earlier Heaven arrangement, paired with images such as "old yin" and "young yang," and symbolized significant meanings. However, in the Later Heaven arrangement, they become subordinate branches of Kan, Li, Zhen, and Dui, used to explain the movement of qi and the magnitude of numbers. Therefore, they are placed in the four corners, no longer occupying central positions as in the Earlier Heaven. The generation and transformation of heaven and earth have their master, and the balance of qi and numbers has its measure: those in proper positions are esteemed, and those in accordance with the season are appropriate. Kan, Li, Zhen, and Dui are both in proper positions and in harmony with the season, capable of encompassing the entire Yi hexagram, like the four seasons of a year or the four directions of the world, forming the main framework. Qian, Kun, Xun, and Gen, on the other hand, are merely details subordinate to the four main trigrams, thus occupying the four corner positions, serving only during the transitional periods between the four seasons. The images they represent naturally differ from those in the Earlier Heaven.

先天以乾坤為主，故二者獨尊；後天以四正為綱，故餘者賤。道有輕重，物有先後。不獨後天之乾坤，非先天比，且所象者亦異於先天，猶洛書之數雖同河圖，而其名類已非河圖之舊。故乾坤在先天為全易主體，在後天則僅一枝節之用，與巽艮同觀。人或疑其退處一隅為不倫，或意其甘退讓為自卑，皆誤也，皆不明後天卦象所取義全異者也。夫後天之乾坤，為本五行之物，推演而得之象，與各卦象同，非復統二氣之乾坤矣。

The trigrams of Heaven and Earth hold a primary position in the Earlier Heaven arrangement, thus occupying a unique status. In the Later Heaven arrangement, the four cardinal trigrams serve as the main framework, and the other trigrams take a subordinate position. The principles have inherent distinctions of importance and sequence. Not only do the trigrams of Heaven and Earth in the Later Heaven arrangement fall far short of those in the Earlier Heaven, but their symbolic meanings are also different. Just as the numbers in the Luo Writing are the same as those in the Yellow River Chart, their names and classifications have changed. Therefore, the trigrams of Heaven and Earth in the Earlier Heaven are the core of the entire Yi system, while in the Later Heaven they have only a secondary role, and should be treated together with the trigrams of Wind and Mountain. Some people doubt that the trigrams of Heaven and Earth being placed in a corner is improper, while others think they willingly step down and take a humble position. These views are incorrect, as they fail to understand that the meaning of the Later Heaven trigrams has completely changed. The trigrams of Heaven and Earth in the Later Heaven are derived from the Five Phases and are of the same nature as the other trigrams, no longer representing the overarching trigrams of yin and yang.

後天二氣之主，以水火當之。水火之外，則皆升降往來之象。乾在西北，坤處西南，其象不過陰陽升降之跡、水火往來之道耳。後天之用，以事物為主，不限於氣，而氣行有形，氣至有質，所象有物，非空言天地也。故後天乾坤，自水火之升降、陰陽之往來，而見其所象之物，不可與先天乾坤等量齊觀。

Later Heaven's yin and yang energies are governed by the trigrams of Water and Fire; the other trigrams merely symbolize the rising and falling movements. The trigram Qian (Heaven) is located in the Northwest, and the trigram Kun (Earth) is located in the Southwest. They merely represent the traces of yin and yang rising and falling, and the channels through which water and fire move. Later Heaven studies focus on concrete things rather than abstract energies; when energy moves, it takes shape; when energy arrives, it takes form. What is symbolized are real objects, not empty talk about heaven and earth. Therefore, the trigrams Qian and Kun in Later Heaven should be understood from the rising and falling of water and fire, and the movement of yin and yang, to see the concrete things they symbolize. They should not be compared directly with the trigrams Qian and Kun in Earlier Heaven.

若不明此義，而仍視如先天，則將坎離混觀，而亂其序；抑將天地顛倒，而失其真，則何以明文王卦位哉？故乾坤巽艮之在後天，正同先天之震巽艮兌，其位序既易，其象數隨殊。此即先後之分、體用之別。學者不可執於名而忘其實，滯於象而遺其位，混先後天而一之，使體用不彰，變化不明，而無以探易之蘊也。

If one does not understand this principle, and continues to view the Later Heaven's Qian and Kun with the perspective of the Earlier Heaven, they will confuse them with Kan and Li, thereby disrupting the order of the Later Heaven; even more so, they may reverse the positions of Heaven and Earth, losing the true nature of the Later Heaven's卦 positions. Then how can one explain King Wen's卦 positions? Therefore, the positions of Qian, Kun, Xun, and Gen in the Later Heaven correspond exactly to the positions of Zhen, Xun, Gen, and Dui in the Earlier Heaven: once the positions have changed, the images and numbers associated with the卦 also differ. This is precisely the distinction between the Earlier Heaven and Later Heaven, as well as the difference between the essential nature and the function. Those who study the Book of Changes should not be rigid in their attachment to the names of the卦 and forget their actual meaning, nor should they be stuck in the images of the卦 and neglect their positions. They must not confuse the Earlier Heaven and Later Heaven as one, leading to confusion between the essential nature and function, and making the changes unclear. In that case, one would be unable to explore the profound essence of the Book of Changes.

文王卦位，以後天二五之氣，分佈天地間而不息。為陽者求於陰而成生育，為陰者近於陽見變化。故繫以分，類以別，正如洛書之數，陰陽次序，分為兩繫，奇偶之數，交錯以行，不似河圖之一氣相環，終始相屬也。蓋動愈久，則變出愈多；生日眾，則類分日繁，有必至之勢也。

King Wen established the positions of the hexagrams by distributing the Later Heaven "two and five" energies—yin and yang energies and the Five Phases energies—throughout the heavens and earth, which continuously move. Those belonging to yang must seek yin in order to achieve generation and reproduction; those belonging to yin must approach yang in order to manifest transformation. Therefore, the hexagrams should be classified systematically and distinguished by categories, just as the numbers in the Luo Writing divide yin and yang in sequence into two series, with odd and even numbers alternating, unlike the Heavens Chart which has a single energy circulating continuously from beginning to end. Generally, the longer the movement continues, the more changes it produces; the more things generated, the more complex the categories become, which is inevitable.

文王之卦，既以坎離震兌分列四柱，則乾坤巽艮自隨之而各屬其類。因後天事物，以形為主，形氣所成，以方為定，二五所生，隨其類而位於一方：水從北，火歸南，木在東，金居西，土行中央而運四季，各有其序也。水與金接，火與木連，風木相依，水天一氣，山土成地而載萬物，相生則承其氣，相制則抗其位，各有其次也。

King Wen arranged the trigrams Kan, Li, Zhen, and Dui as the four main pillars. Consequently, Qian, Kun, Xun, and Gen naturally fell into their respective categories. Since Later Heaven is based on physical forms, all things composed of form and qi must be determined by direction; the things generated by yin and yang and the Five Phases are thus placed in specific directions according to their categories: water belongs to the north, fire to the south, wood to the east, metal to the west, and earth in the center, circulating through the four seasons. Each has its own order. Water and metal connect with each other, fire and wood are linked, wind and wood are interdependent, water and heaven share the same qi, and mountain and earth form the land to support all things. Those that mutually generate receive each other's qi, while those that mutually control oppose each other in position, each following its own order.

故先天乾為天，包舉宇宙，後天則屬金，建位西北；先天坤為地，載育群倫，後天則屬土，序次西南。南為離火，與土相生；北為坎水，與乾相得。而西方之兌屬金，亦生自土而類於乾。艮為山，為氣之終，與土同類，而水泉潛焉。震為木之生地，木雖生於水，必得土之培，故自山出。巽亦木也，風之所見；風亦氣也，火之所燃。其性相宜，其位相接，故成環也。

Therefore, the Qian hexagram of the Earlier Heaven represents Heaven, encompassing the entire universe; in the Later Heaven, it belongs to the Metal element and is located in the Northwest. The Kun hexagram of the Earlier Heaven represents Earth, nurturing all creatures; in the Later Heaven, it belongs to the Earth element and is situated in the Southwest. The South is Li fire, which generates Earth; the North is Kan water, which generates Metal and thus harmonizes with the Metal of Qian. The Dui hexagram in the West also belongs to Metal, and is generated by Earth, thus being similar to Qian. The Gen hexagram represents mountain, the end of the movement of qi, and is similar to Earth, with underground springs hidden within it. The Zhen hexagram represents the place where wood grows; although wood is generated by water, it must be cultivated by Earth, so it grows from the mountain. The Xun hexagram also belongs to wood, being the place where wind manifests; wind is qi, which is what fire relies on to burn. These hexagrams are harmonious in nature and adjacent in position, thus forming a circular connection.

水為火仇，金為木敵，土受木制，金被火刑，水逢土掩，氣為風搖，相異其性，相抗其位，相制其能，相隔其次，故成錯也。環則氣順生成，錯則氣變化見。分則為四為八，推之無盡；合則為五為二，返之太極。此固後天自然之象，亦文王卦位次之所定也。

Looking at it in reverse: water is the enemy of fire, metal is the master of wood, earth is subdued by wood, metal is melted by fire, water is buried by earth, and qi is disturbed by wind. Their natures are opposite, their directions are opposing, their functions are mutually restraining, and their sequences are mutually separated, thus forming a situation of mutual crossing. The aspect where they form a continuous loop allows qi to flow smoothly and generate all things; the aspect where they cross each other allows the transformation of qi to be revealed. Separately, they are the Four Symbols and the Eight Trigrams, and their derivation has no end; together, they are the Five Phases and the Two Principles, and their return leads back to the Taiji. This is naturally the state of Later Heaven, and it is precisely the basis for the order of the hexagrams as established by King Wen.

且文王卦，為推伏羲卦之用，而盡其變也，即本先天氣數，推至後天事物，以求其遞嬗之跡也。故伏羲卦位次為易之體，文王卦位次為易之用。因用得體，因體得用，原無二致，則伏羲卦之位次，即文王卦之前身；而文王卦之位次，即伏羲卦之變象。二者一而二也。由其異以求其同，知其同以辨其異，此習易者之所先務，而不可不通之為一，以明其旨之所在，與象之所示也。

Furthermore, the positions of the hexagrams in the Book of Changes attributed to King Wen were intended to expand the function of the hexagrams from Fuxi, pushing their transformations to their ultimate extent. This was done by following the qi and numbers of the Earlier Heaven and proceeding all the way to the Later Heaven's specific phenomena, in order to trace the mutual transformation between the two. Therefore, the positions of the hexagrams from Fuxi represent the essence of the Book of Changes, while the positions of the hexagrams from King Wen represent its function. From function one can perceive the essence, and from the essence one can understand the function; the two are essentially the same. The positions of the hexagrams from Fuxi are the original form of the hexagrams from King Wen, and the positions of the hexagrams from King Wen are the manifested form of the hexagrams from Fuxi. It is acceptable to regard them as one or as two. One should first seek the commonality from their differences and then distinguish their differences based on their commonality. This is the primary effort required for those studying the Book of Changes. Only by integrating the two can one understand the fundamental principles and the meanings conveyed by the hexagrams.

如文王八卦之序自震始，與伏羲似同，而一則出於坤，為陽始生；一則變於艮，為陽已動，是不同也。蓋先天之氣，一六為水，三八為木，其序同也；後天之物，因土制水，因水生木，其用殊也。故甲乙為木，必得壬癸之生源，而甲已化土，方成生化之大用。若徒水不生木也，有土以培之，有山以蓄之，則水用見，而木道成，此後天之序，有異於先天，

For example, the order of the trigrams in the King Wen's arrangement starts with Zhen, which appears similar to the trigrams in Fuxi's arrangement. However, one originates from Kun, indicating the initial emergence of yang energy, while the other comes from Gen, indicating that yang energy has already begun to move, thus making them different. The Earlier Heaven arrangement discusses energy: one and the Six Harmonies form water, three and eight form wood, and the order is the same in both cases. The Later Heaven arrangement discusses things: it requires earth to control water and water to nourish wood, resulting in different functions. Therefore, the heavenly stems "Jia" and "Yi" belong to wood, but they must be supported by the water stems "Ren" and "Gui" as the source for their growth. Furthermore, "Jia" combines with "Ji" to form earth, enabling the full function of generation and transformation. If there is only water, it cannot alone produce wood; there must be earth to cultivate it and mountains to contain it, allowing the function of water to be revealed and the growth of wood to be completed. This is why the order in the Later Heaven differs from that in the Earlier Heaven.

而震坤之位，有殊於前象者也。先天生化本乎氣，故五行順序；後天生化存乎形，故五行錯行。一年之序之自春始，一日之氣自寅見，一地之氣自東起，故後天以震司動令也。動者自靜出，則震必自艮出。艮者止也。由動而止於靜，此艮為氣之終；由靜而漸於動，則艮又氣之始。故艮者始終之地。先天以艮入地，後天以艮出水，故艮之先後天，皆為終始之樞，而在後天尤至顯也。

This is why the trigrams Zhen (Thunder) and Kun (Earth) differ in their positions between the Earlier Heaven and Later Heaven arrangements. In the Earlier Heaven arrangement, the process of generation and transformation is based on qi, so the Five Phases are arranged in the order of mutual generation. In the Later Heaven arrangement, the process of generation and transformation occurs in form, so the Five Phases intermingle and move in a different sequence. The order of a year begins with spring, the qi movement of a day begins at the hour of Yin, and the qi flow of a region begins from the east, hence the Later Heaven uses the trigram Zhen to govern the time of movement. Since all movement originates from stillness, the trigram Zhen must arise from the trigram Gen. Gen signifies stopping: movement leads to stopping in stillness, so Gen is the end of qi; stillness gradually leads to movement, so Gen also becomes the beginning of qi. Therefore, Gen is the meeting point of beginning and end. In the Earlier Heaven arrangement, Gen is placed at the point of entering the earth, while in the Later Heaven arrangement, Gen is placed at the point where water qi emerges from the earth. Thus, Gen serves as the hub between beginning and end in both the Earlier Heaven and Later Heaven arrangements, and this is especially evident in the Later Heaven.

東北之方，正生機所息，如春之先、冬之盡也；山土之中，正生物之所始，如木之根、草之荄也。故艮者，萬物之所資以生育者也。其同者則為坤，故與抗位，然後天之序分相次也。以升降言，則坤艮相對；以出入言，則巽艮相當。巽為風木，草也，氣也。草木之出於地，已異於艮之根荄；風氣之流於空，卻近於乾之金氣，故與乾對，而同艮比。

The northeast direction is where vitality lies hidden and rests, much like the period before spring arrives or just before winter ends; in the soil of the mountains, it is where living things begin to sprout, similar to the roots of trees and the overwintering roots of wild grass. Therefore, the Gen trigram represents the foundation upon which all things rely for growth and development. The Kun trigram, which also belongs to earth, is paired with Gen, and they are placed opposite each other, facing each other, which is the arrangement of order in the Later Heaven. In terms of rising and descending, Kun and Gen are opposite; in terms of entering and exiting, Xun and Gen correspond. Xun represents wind and wood, as well as grass and qi. Grass and trees emerging from the ground have a form different from the roots and overwintering roots that Gen represents; wind moving through the void is closer to the metal qi of the Qian trigram, so Xun is opposite Qian and is adjacent to Gen.

乾為氣，若天空之氣，與水一類，化而為水，凝而為金，位在坎兌間，則西與北之相生也。次於西北方，則淨土之天所在也。佛稱淨土在西方，而佛身金剛不壞，佛相非空非色，其義與乾象同。佛言四大，地水火風，獨少金，而以西方淨土為佛地，亦與五行之言一也。故乾為天，而性屬金，而以西北，與巽對。

The trigram Qian represents qi, just like the atmospheric qi in the sky, and belongs to the same category as water: when dispersed it becomes water, and when condensed it becomes metal. Its position is between Kan and Dui, exactly where the western and northern regions of metal and water interact through mutual generation. It is placed in the northwest, which is considered the location of the "Pure Land Heaven." Buddhism says the Pure Land is in the west, and also describes the Buddha's body as being like a diamond, indestructible, and the Buddha's form neither empty nor material, which aligns with the imagery of the Qian trigram. Buddhism speaks of the "Four Great Elements," listing earth, water, fire, and wind, but omitting metal, yet it designates the western Pure Land as the Buddha's realm, which coincides with the Five Phases theory. Therefore, the Qian trigram represents heaven, and its nature belongs to metal, placed in the northwest, facing the Xun trigram in the southeast.

以用言，則與坤對。坤司載物，乾司覆物。坤為生，乾為化。乾知大始，坤代有終，皆功用之相當也，故位相比。此亦先後天之同異也。在五行生制中，萬物生化以成，固氣之所推蕩也。八卦之分五行以象物，因二氣生降消長，以象生化之跡，而以後天之卦為最明顯。

If we consider their functions, Qian and Kun are opposites: Kun is responsible for supporting all things, while Qian is responsible for covering all things; Kun governs generation, and Qian governs transformation. The "Great Treatise" of the Upper Canon says, "Qian knows the beginning of great things, and Kun completes the formation of things." Here the meaning is that Qian initiates the beginning of all things, while Kun continues the process so that things have an end. These are aspects of their functions that are mutually corresponding, hence the two trigrams are adjacent in position. This is also an example of the relationship between Earlier Heaven and Later Heaven, which are both the same and different. In the operation of mutual generation and mutual control among the Five Phases, all things are successively generated, and this is the result of the movement and agitation of qi. The Eight Trigrams are assigned to the Five Phases to symbolize specific things, following the rise and fall, increase and decrease of the two energies, yin and yang, to indicate the trajectory of generation and transformation. This is most clearly reflected in the Later Heaven arrangement of the trigrams.

蓋先天之卦，為示氣之本體，與其行至之序，非如後天均可按之事物也。後天卦象，全體生化，有行至之序，有變遷之跡，有相生制之象，有相循環之式。故分觀之，則一節一方之物；合觀之，則全部全體之事，均貫通者也。

The earlier heaven trigrams are meant to show the essence of qi and the order in which it moves and reaches. Unlike the later heaven trigrams, they do not correspond to specific things that can be verified in every aspect. The later heaven trigrams encompass the entire process of generation and transformation: they include the order of qi movement and the path of change, as well as the images of mutual generation and mutual control, and the pattern of continuous cycles. When viewed separately, each trigram corresponds to a specific season and direction; when viewed together, they represent the whole and overall principles, with everything interconnected.

如先天之卦，天地水火對列，山澤風雷抗居，其氣佈於兩間，其數分於萬物，而不相聯接也，故分為二，以屬於乾坤。後天則不然，以水火為主，金木為輔，四隅相錯，皆相接也。因後天之象，由合而分，本無窮盡，雖本先天一氣，可統於陰陽，而應五行生化，可變為萬用。故水火司乾坤之用，金木助陰陽之功，功用以全，物事以備。

For example, in the Earlier Heaven hexagrams, heaven and earth, water and fire are paired opposite each other, mountain and marsh, wind and thunder are opposed to each other. Their qi is distributed throughout heaven and earth, their numbers are allocated among all things, yet they are not connected to each other. Therefore, they are divided into two groups of yin and yang, each group belonging to Qian and Kun. However, in the Later Heaven, it is different: water and fire are the main elements, metal and wood are the auxiliary ones, and the four corner hexagrams are interwoven among them. They are all connected to each other. Because the image of Later Heaven comes from combination and then division, it has no end. Although it originates from the single qi of Earlier Heaven and can be summarized under yin and yang, once it is applied to the generation and transformation of the Five Phases, it can produce countless uses. Therefore, water and fire take on the functions originally belonging to Qian and Kun, while metal and wood assist yin and yang in completing their tasks, thus making the functions complete and things fully established.

在先天以元氣為貴，故乾包坤；而後天以生化為先，故陰先陽，此離上坎下，與乾上坤下各不同也。生化之用，以陽求陰，得陰始生，陽不獨生也，故曰陰陽。而上離下坎，離陰以代乾，坎陽以代坤，陰陽互濟，生化乃見，此實天下至理，萬物大本，而後天卦象位次之要義也。

In the Earlier Heaven arrangement, primordial qi is considered most important, hence the Qian trigram encompasses the Kun trigram. In the Later Heaven arrangement, generation and transformation take precedence, so yin comes before yang—this is why in the Later Heaven arrangement, the Li trigram is above and the Kan trigram is below, opposite to the Earlier Heaven arrangement where Qian is above and Kun is below. The function of generation and transformation is that yang seeks yin; only by obtaining yin can something be generated. Yang alone cannot produce offspring, so it is called "yin and yang." Thus, the upper position is occupied by the Li trigram, which has an outer yang and an inner empty space containing yin, taking the position of Qian as yin; the lower position is occupied by the Kan trigram, which has an outer yin and an inner solid space containing yang, taking the position of Kun as yang. Yin and yang support each other, enabling generation and transformation to manifest. This is truly the highest principle in the world, the fundamental basis of all things, and the most important meaning behind the arrangement of Later Heaven trigrams.

若仍如先天之象，則生化不成，氣數不續，道之窮也。窮則必變，變則後天之象見，此文王之卦，必繼伏羲而明，而離坎之位必代乾坤而立者也。物變必因陰陽之交，事變必因氣數之易，天地尚不得不變，況下者乎。後天者變象也，變於先天，而成現在之象，故人道存焉。人道以為主，則乾坤退用，此離坎屬人，為後天位次之樞，而主八卦之用也。學者當思之。

If the trigrams remained as in the Earlier Heaven, generation and transformation would not be completed, and the cycle of qi and numbers would not be continued. This is when the Dao reaches its end. When the Dao reaches its end, transformation is inevitable. Once transformed, the Later Heaven trigrams appear. This is precisely why King Wen's trigram positions must follow Fuxi and clarify them, and why the positions of Li and Kan must replace Qian and Kun. All changes in things are due to the meeting of yin and yang; all changes in affairs are due to the transformation of qi and numbers. Even heaven and earth cannot avoid change, so how much more so can the myriad things under heaven and earth? The Later Heaven trigrams are the trigrams after transformation; they come from the Earlier Heaven and form the appearance we now see. Thus, the human Dao exists within them. Since the human Dao is the main focus, Qian and Kun take a secondary role. Therefore, the trigrams Li and Kan belong to humanity and become the central points of the Later Heaven order, governing the functions of the eight trigrams. Those who study the Book of Changes should thoroughly understand this.