In the Great Treatise, the first part asks: What is the purpose of the Book of Changes?

子曰：夫易何為者也？

Confucius asked: What is the purpose of the book called The Zhou Changes?

義曰：自此以下至「民咸用之謂之神」為一章。此十翼之中第十。子曰夫易何為者，此蓋孔子嘆大易之道其功深賾，故假設此發問之辭以問之，曰夫易者何為者也。

Hu Yuan explains: From here onwards, until the text 'The people all use it and call it divine' is reached, this constitutes one chapter, positioned as the tenth in the Ten Wings. The sentence 'Zi Yu: Fu Yi He Wei Zhe' is Confucius praising the profound and mysterious utility of the Way of the Zhou Changes, and therefore deliberately setting a question to begin with, saying: What is the purpose of the Book of Changes?

夫易開物成務，冒天下之道，如斯而已者也。

The Zhou Changes is a book used to open the aspirations of all things, accomplish the affairs of the world, and encompass all the principles under heaven. That is all.

義曰：此夫子自釋易之體用也。開者，通也；冒者，覆也。言大易之道其功宏博，能開通於萬物之志，成就夫天下之務，覆冒夫天下之物也。至如泰卦則言財成之義，履卦則言履素之宜，革卦則言治厯之事，鼎則言鼎新之，旅則言無敢折獄，遯則言遯尾之厲，大壯則言君子用罔，乾卦則言亢龍有悔者。如此之類，是皆開通萬物之志，成就天下之務，覆冒天下之道。如斯之道，則大易之體用也，故云如斯而已。

Hu Yuan explained: This is Confucius' own explanation of the essence and function of the Yi. "Kai" means to open, and "mao" means to cover. The way of the Zhou Yi is vast and profound, capable of opening the aspirations of all things and accomplishing the affairs of the world, and covering all things under heaven. For example, the Tai hexagram discusses the proper measure of the way of heaven and earth, the Li hexagram discusses the appropriate conduct of maintaining one's proper position, the Ge hexagram discusses the reform of calendars and the clear distinction of the four seasons, the Ding hexagram discusses the renewal of old things, the Lu hexagram discusses not lingering in lawsuits, the Duan hexagram discusses the danger of retreating and falling behind, and the Da Zhuang hexagram discusses the gentleman not being overbearing. Such examples all illustrate the opening of the aspirations of all things, the accomplishment of the affairs of the world, and the covering of the correct way. These are precisely the essence and function of the Zhou Yi, hence it is said, "This is all."

是故聖人以通天下之志。

Therefore, the sage used the Zhou Changes to connect the hearts and minds of people throughout the world.

義曰：夫大易之道其功廣大，是故聖人以此之故以通達天下之志者也。然則天下之人心志至眾至繁，而聖人以大易之道以通天下之志者何也？蓋聖人有深幾之見，極未形之理，以已之心可以見天下之心，以已之志可以見天下之志。雖天下之人心志至眾至繁，然聖人以已之幾深度人之情偽利害，極未形之理，可以見天下之志者也。

Hu Yuan explained: The principles of the Zhou Changes have broad effects, so the sages used them to understand the hearts and aspirations of people throughout the world. However, human thoughts are so numerous, yet the sages were able to comprehend them all through the principles of the Zhou Changes. Why is this so? Because the sages had profound insight, able to investigate the origins of things before they took shape, and thus their own hearts illuminated the hearts of all people, and their own aspirations illuminated the aspirations of all people. Even though the hearts and aspirations of people are numerous, the sages, with their ability to discern the subtle and understand the underlying truths, deeply considered the authenticity and interests of human affairs, and thus comprehended the hearts and aspirations of all people.

以定天下之業。

Using the Zhou Changes to establish a great cause under heaven.

義曰：言聖人以此大易之故，極其幽深，研幾，成天下之務，冒天下之道，以定天下之功業也。

Hu Yuan explained: The sage, relying on The Zhou Changes, thoroughly investigates the profound principles and explores the subtle beginnings, thus accomplishing the affairs of the world, covering the correct path of the world, and ultimately establishing the achievements of the world.

以斷天下之疑。

Use the Zhou Changes to decide the doubts and difficulties of the people under heaven.

義曰：言大易之道通於人事。一卦六爻，有得位失位者，然吉凶悔吝雖聖人亦有所不知，於人事之間不能無疑。是故聖人雖以其蓍策占筮之，然亦不能無疑惑之心，而又謀之於鬼神，謀之於天地，以成其卦爻，又於卦爻之下繋屬其文辭，以決斷天下之疑也。至如乾之初九言潛龍勿用，離之六四言突如其來，如此是斷其疑也。

Hu Yuan explained: The principles of The Zhou Changes apply to human affairs. In a single hexagram with six lines, some are in proper positions and some are not. Among these, the auspicious and ominous outcomes are even beyond the knowledge of sages, and people involved in worldly matters often have doubts. Therefore, although sages have already used the yarrow stalks for divination, they still have lingering uncertainties in their hearts. Thus, they consult ghosts and spirits, and seek evidence from heaven and earth, and based on this, they establish the hexagram and its lines. Then they add explanatory texts beneath the hexagram and its lines, to resolve the doubts of people throughout the world. For example, the line 'The dragon is hidden and does not act' in the first line of the Qian hexagram, and the line 'The fire suddenly arises' in the fourth line of the Li hexagram, are both examples of such explanatory texts that resolve doubts.

是故蓍之徳圓而神。

Therefore, the virtue of the yarrow stalks is circular and flowing, profound and mysterious.

義曰：夫蓍策之數未占已前，其吉凶悔吝人皆不可見，無有窮極，無有定止，其通變之道、天地之宜，其用如神，運而不窮，周流通暢也。

Hu Yuan explained: Before the divination is performed, the number of the yarrow stalks does not reveal good fortune, ill fortune, regret, or hardship. It is neither exhausted nor fixed. Its way of transformation and its measure in harmony with heaven and earth operate like the divine, ceaseless and flowing smoothly.

卦之徳方以知。

The virtue of the trigrams is square and definite, yet capable of clear discernment.

義曰：言蓍策之數未占之時雖其用如神，其吉凶悔吝周流通變，運而不窮；及其揲蓍之後布成其卦，卦有六爻，卦爻之下有得位、有失位、有中、有正、有凶、有吉、有悔吝，皆繋屬而不可變動，故言方以知者，是知其過去未來之事，極其未形之理，其情偽利害盡可見矣。然則必言蓍徳圓而神、卦徳方以知者，蓋神以知來，是來無方也；知以藏徃，是徃有常也。物既有常，猶方之有止；數無常體，猶圓之不窮。故蓍之變通則無窮，神之象也；卦觧爻分有定體，知之象也。知可以識前言徃行，神可以逆知將來，故蓍以圓象神，卦以方象知也。

Hu Yuan explained: The number of the yarrow stalks is indeed as divine as the heavens when not yet used for divination, with fortune and misfortune, regret and hardship flowing and changing endlessly. But once the process of "shie zhi" is completed, that is, when the yarrow stalks are repeatedly divided and counted in groups of four to determine the lines and arrange them into a hexagram, the six lines of a hexagram are fixed. Each line has its proper position, its improper position, its central position, its correct position, and it has both good and bad, as well as those that carry regret and hardship. All these are fixed and cannot change anymore. Therefore, the virtue of the hexagram is square and clear-sighted: it clearly perceives past and future events, pushing the principles of things to their extremes, and seeing clearly the authenticity of human feelings and the advantages and disadvantages of situations. As for why it is said that the virtue of the yarrow stalks is round and divine, and the virtue of the hexagram is square and wise, it is because divination is used to foresee the future, which has no fixed direction; wisdom is used to remember the past, which has a fixed pattern. Things have fixed patterns, just as a square has edges and a definite shape; numbers have no fixed form, just as a circle moves endlessly. Therefore, the changeability of the yarrow stalks has no end, which is the image of divinity; when a hexagram is divided and its lines are fixed, it has a definite shape, which is the image of wisdom. Wisdom remembers past words and actions, while divination foresees the future, so the circle is used to symbolize the divinity of the yarrow stalks, and the square is used to symbolize the wisdom of the hexagram.

六爻之義易以貢。

The meanings contained in the six lines of the hexagram are communicated to people in detail through the words of the Zhou Changes.

義曰：貢者，告也。言聖人因蓍策之數以佈設六十四卦，卦有六爻，以盡萬物之理。然爻有應有不應，有正有不正，其間吉凶悔吝皆不能告諭於人，故大易之道極未形之理，知過去將來之事，故六爻之下皆繋屬文辭，以貢告於人也。至如比之初六言吉，大過上九言凶，如此之類，是皆告於人，使人從善而去惡，從吉而去凶也。

Hu Yuan explained: "Gong" means to inform. The sage arranged the sixty-four hexagrams according to the numbers of the divination sticks, each hexagram having six lines, in order to exhaust the principles of all things. However, between the lines there are corresponding and non-corresponding ones, appropriate and inappropriate ones. The auspiciousness, misfortune, regret, and hardship of the lines cannot be explained merely by looking at their positions. Therefore, the way of the Zhou Changes is to push the unformed principles to their extremes and to reveal past and future events. Thus, beneath each of the six lines, there are words attached, to inform people. For example, the first line of the "Compare" hexagram says "auspicious," and the top line of the "Great Excess" hexagram says "inauspicious." Such phrases are meant to inform people, so that they may follow the good, avoid the evil, tend toward the auspicious, and flee from the inauspicious.

聖人以此洗心。

The sage used this book of The Zhou Changes to purify his mind.

義曰：夫大易之道至公至正，極天地之理，盡人事之宜，其吉凶悔吝皆繋屬於諸卦爻之下，聖人觀之，可以洗盪其心。至如萬物有疑則卜之，是洗盪其疑心；行善則吉，行惡則凶，是洗盪其噁心也。既洗盪己之心，然後可以洗盪萬物之心也。

Hu Yuan explained: The way of the Zhou Changes is extremely impartial, investigating the principles of heaven and earth to their utmost, and thoroughly explaining the proper measures of human affairs. All good fortune, misfortune, regret, and hardship are attached to each hexagram and line. The sage can use them to purify his mind. For example, when there is doubt about a matter, one consults the oracle, which removes doubt from the mind. Understanding that doing good leads to good fortune and doing evil leads to misfortune removes evil thoughts from the mind. One must first purify his own mind before he can talk about purifying the minds of people throughout the world.

退藏於宻。

After use, they are gathered up and returned, with the divine essence hidden in a secret and concealed place.

義曰：言此大易之道索隱窮神，能盪滌萬民之心，雖有吉凶悔吝之變、仁義之術，而人不知自用，是其功如神之藏宻也。故上文所謂顯諸仁、藏諸用者，此也。

Hu Yuan explained: The Way of the Zhou Changes seeks out the hidden and explores the subtle, capable of purifying the hearts of the people. Though it contains various changes of auspiciousness, misfortune, regret, and hardship, as well as various methods of practicing benevolence and righteousness, the people use it every day without realizing it. This is precisely why its function is profound and hidden. The previous statement about revealing benevolence and concealing function refers to this.

吉凶與民同患。

It shares the joys and sorrows, blessings and misfortunes of the people.

義曰：夫人之生，愚夫愚婦者甚眾，其性昏蒙，憧憧然不知所以然而然，舉動之間雖有凶咎悔吝之事而不知自止。是故聖人以此大易之故，明示其吉凶憂患，使趣其善者舍其惡，向其吉者背其凶，是大易之道與民同憂患也。

Hu Yuan explained: There are many people in the world with shallow understanding, both men and women, whose minds are confused and who are constantly busy coming and going, yet they do not know why things are like this. When their actions clearly bring about misfortune and regret, they still do not stop. Therefore, the sage used the Zhou Changes to clearly show them the distinction between good and bad fortune and worries, guiding them to pursue goodness and abandon evil, to seek good fortune and avoid danger. This is the way of the Zhou Changes, sharing the concerns of the common people.

神以知來。

By means of its marvelous aspect, it knows in advance what is about to come.

義曰：言大易之道知其未來之事，明其未形之理，故其用如神也。

Hu Yuan explained: The way of the Zhou Changes can know things that have not yet happened, and illuminate the principles that have not yet taken form, so its function is like that of a divine being.

知以藏徃。

By using wisdom, one reflects on past events.

義曰：言此大易之道因蓍之策知其過去已形之理，其妙皆知之也。然則必言知來藏徃者，蓋蓍定數於始，於卦為來；卦成象於終，於蓍為徃。

Hu Yuan explained: The way of the Zhou Changes depends on the number of the divination stalks, enabling one to know the principles that have already taken shape in the past. Its subtleties are all clear. The reason for distinguishing between knowing the future and concealing the past is that at the beginning of the divination, the stalks determine the number, which relates to the future; but once the divination is completed, the hexagram is formed, which, in relation to the stalks, has already become the past.

其孰能與於此哉！古之聰明叡知、神武而不殺者夫。

Who else could reach such a level? Perhaps only those of old who were keen-sighted and wise, with thoughts flowing smoothly and unimpeded, mighty like gods yet never resorting to warfare.

義曰：言大易之道神以知來，知以藏徃，非此之故，其孰能與於此哉？惟是古者聰明叡知之人可以與之。耳無所不聞，故曰聰；目無所不見，故曰明；思無所不通，故曰叡；才無所不及，故曰知。言惟是聰明叡知之人有文有武，既能察微，又有剛斷，故於大易之間卦爻之下各隨動靜，神其吉凶之事，明其威福之理，示人以信，則人自然而威服之。至如弧矢取諸睽，刑罰取諸噬嗑，如此之類，皆是神其威武，不用刑殺而天下自然威服也。

Hu Yuan explained: The way of the Zhou Changes depends on divine insight to foresee the future and on wisdom to preserve the past. Without relying on it, who else could achieve this? Only the ancient wise and intelligent are worthy of it. The ear has nothing it cannot hear, hence it is called "Cognizant"; the eye has nothing it cannot see, hence it is called "Bright"; contemplation has nothing it cannot comprehend, hence it is called "Reverent"; ability has nothing it cannot reach, hence it is called "Knowledge." This means that only those who are both wise and intelligent, possessing both literary virtue and military strategy, capable of discerning minute details and resolute in decision-making, can in the Zhou Changes, with the movement of the hexagrams and lines, speak of auspicious and inauspicious matters with divine precision, and explain clearly the principles of punishment and reward. They present sincerity to others, and people naturally revere and obey. For example, making bows and arrows by following the Kui hexagram, and establishing punishments by following the Shihe hexagram; such practices employ authority skillfully without actual execution of punishment, and the world naturally fears and submits.

是以明於天之道，而察於民之故，是興神物以前民用。

Therefore, they understood the patterns of heavenly movement and observed the actual conditions of people's lives, so they used divination tools like the yarrow stalks and turtle shells, these sacred objects, to guide the people before they took action.

義曰：言聰明睿知之人既能神其威武而不殺，是以大明天地陰陽變化之道，大察天下情偽利害之故，又以神靈之物明其吉凶之驗，以前萬民之用，至於未來之事皆繋屬其辭，使人通曉之，趣其善而去其惡者也。

Hu Yuan explained: A wise and intelligent person, having mastered the art of using authority skillfully without resorting to violence, can thereby greatly illuminate the principles of yin and yang transformations in heaven and earth, and deeply understand the true nature and interests of people across the world. He also uses divination tools like the tortoise shell and yarrow stalks to reveal omens of good or bad fortune, guiding the people before they take action. Even matters that have not yet occurred are recorded in words, making them clear and understandable, so that people can follow the good and abandon the evil.

聖人以此齋戒。

The sages used this book of The Zhou Changes to purify their bodies and minds, and to be cautious and vigilant against potential dangers.

義曰：洗心則謂之齋，防患則謂之戒。言聖人以此大易之道齋心防戒其患害之事，使憂虞悔吝不能及於己，至幽至微之處皆得以先知也。

Hu Yuan explained: To purify the mind is called "zhai," and to guard against calamities is called "jie." The sages use the principles of the Zhou Changes to cleanse their hearts and guard against misfortunes, so that worries and regrets do not touch them. Even the most hidden and subtle aspects can be foreseen in advance.

以神明其徳夫。

And make one's virtue become profound and enlightened.

義曰：言聖人既能以大易之道齋戒而防患，又能觀易道幽深，以神明其徳，使天下之人不知所以然而然也。

Hu Yuan explained: The sage can use the principles of the Zhou Changes to purify his body and mind, prevent problems before they arise, and comprehend the profound nature of the Yi doctrine, making his virtue mysterious and flourishing, enlightening the people across the land, yet he cannot explain how these changes come about.

是故闔戶謂之坤。

So close the door, which is called Kun.

義曰：此以下又廣明大易自乾坤而來也。夫坤者陰也，主夫地。然坤之道主夫生成萬物，若陽降其氣，則坤能成而生之；若陽氣不降，則地道闔閉，主其収藏，如戶之閉也。

Hu Yuan explains: From here on, it further explains that the entire Zhou Changes arises from Qian and Kun. Kun belongs to Yin and governs the earth. The function of Kun is to generate all things: when the Yang energy descends, Kun receives it and forms all things; when the Yang energy does not descend, the Dao of Kun closes off, turning to govern storage, like a door closing.

闢戶謂之乾。

Open the door, and this is called Qian.

義曰：乾者陽也，主夫天。夫天陽之氣下生萬物，使萬品之物皆遂其生者，是乾為開闢之端，如戸之開通者也。然則先言坤而後言乾者，蓋凡物先藏而後出，故先言坤而後言乾也。

Hu Yuan explained: Qian belongs to Yang and governs Heaven. The Yang energy of Heaven descends to nurture all things, allowing various living beings to fulfill their vital energies, which is the aspect of Qian that opens the way, like a door being opened and becoming unobstructed. As for why Kūn is mentioned before Qian, it is because all things first conceal themselves and then emerge, so Kūn is discussed first and Qian comes after.

一闔一闢謂之變。

One gate opens and one closes alternately, which is called transformation.

義曰：言陰主其閉闔，又主其収藏；陽主其開闢，又主其施散。是一闔一闢以成變化之道，春生夏長秋成冬乾者也。

Hu Yuan explains: Yin governs closure and storage, while Yang governs opening and dispersion. The alternation of unity and separation, opening and closing, gives rise to the way of change. In terms of the seasons, this manifests as spring for growth, summer for development, autumn for maturity, and winter for withering.

徃來不窮謂之通。

Coming and going without end, this is called communication.

義曰：言天地之道、生成之理，徃來之間循環不絶，周而復始，無有窮極，常自通流，是謂之通也。

Hu Yuan explained: The principles of the operation and generation of heaven and earth are in a continuous cycle of coming and going, circulating without end, recurring endlessly, and perpetually flowing, which is called communication.

見乃謂之象。

The step that becomes apparent is called the image.

義曰：言天地之道、陰陽之功生而不已，自十一月建子陽氣下復，至於丑寅之位，萬物顯見於世，有其形狀，故謂之象也。

Hu Yuan explained: The way of heaven and earth, the function of yin and yang, continues endlessly. Starting from the eleventh month, the Month Builder is Zi, and the yang energy begins to return from below. By the time we reach the Chou and Yin months, all things appear in the world, taking on visible forms, hence it is called "image."

形乃謂之器。

The step of forming a shape is called the vessel.

義曰：言天地之道生成不已，故萬物始有其形，形之不已，乃可成於器用。是故聖人因此大易六十四卦之形象，凡創制器用，必觀其形象，為之凖範，然後成其法式也。

Hu Yuan explained: Heaven and Earth continuously generate myriad things, and thus things take form. With continuous filling of form, they can become useful objects. Therefore, sages, when creating objects, always first observe the images of the sixty-four hexagrams in the Zhou Changes, taking them as a standard, and then determine the method of making.

制而用之謂之法。

Cutting and shaping it into an object for use is called a method.

義曰：言聖人裁制其物，凡所施用，垂為範模，後世以之為法式也。至如宮室取大壯，網罟取諸離，書契取諸夬，弧矢取諸睽，如此之類，皆是聖人制成器用，為後世之法。

Hu Yuan explained: The sages made objects and tools, and whatever they created for use was passed down as a model, for later generations to follow as a standard. For example, building palaces and houses followed the principle of Da Zhuang, making nets with ropes followed the principle of Li, carving wooden signs for record-keeping followed the principle of Guai, and making bows and arrows followed the principle of Kui. All these are examples of sages creating tools and instruments, establishing principles for future generations.

利用出入，民咸用之謂之神。

The tools and objects are convenient, allowing people to take them out and use them without any difficulty. Everyone uses them but cannot explain why. This is called the "spirit" (shen).

義曰：言聖人既制器用，或出於此，或入於此，使天下之人用之皆得其利。天下之人既皆得其利，是聖人之妙用如神，而人不知所以然而然也。

Hu Yuan explained: The sages having already created tools, some go out from here, some come in from here, and all people use them without any inconvenience. Since all people have gained convenience, it shows that the subtle skill of the sages is like the divine, people follow it but cannot explain the reason.