Image: Wellcome Collection (Public Domain)
TL;DR: The I Ching is an Eastern philosophical text built on two symbols, the yin and yang lines, which combine into the eight trigrams and 64 hexagrams, modeling the movement patterns of the universe. The word "Dịch" means change, and that is the central thread of the entire book. The origin of the lines remains debated, but their symbolic meaning goes far beyond any theory of sexuality or divination.
What is the I Ching?
The I Ching, often called the Zhou Yi, is one of the oldest and most profound books of humanity. Its international name is the I Ching. The word "Yi" means change, and that is the central axis of thought for the entire book: all things move without ceasing according to law. Unlike purely philosophical works, the I Ching does not present its doctrine through lengthy reasoning but uses a distinctive system of symbols: yang lines (solid lines -) and yin lines (broken lines --). From these two basic signs, the ancients built the eight trigrams (bat quai, the eight single trigrams), then combined them into the 64 hexagrams (luc thap tu quai), encompassing every law of transformation of heaven, earth and human life.
If we regard the universe as a taiji: an initial state of chaos: then taiji gives rise to two opposing energies, yin and yang (the two modes). These two energies interact, push and rub against each other without ceasing, creating all movement. That interaction is encoded into the trigrams, and the I Ching is precisely a mirror reflecting the operating laws of the universe, helping people understand the world and understand themselves.
What are the two layers of text in the I Ching?
The I Ching is not a single uniform body of text but consists of two distinct layers. The first layer is the Jing (classic) portion: each hexagram has its own name, a hexagram statement (guaci, which many Vietnamese books call the tuan statement) and six line statements (yaoci). Together that makes 64 hexagram statements and 384 line statements, plus the Use of Nine of the Qian hexagram and the Use of Six of the Kun hexagram. The second layer is the Zhuan (commentary) portion, that is the Ten Wings, ten treatises that explain and develop the thought of the classic portion.
If you want to go deeper into how to read each hexagram in sequence, you can see In what order should one read an I Ching hexagram. And to understand the role of the ten commentaries, please read The Ten Wings: the ten treatises of the I Ching.
What is the origin of yin and yang lines?
What are yin lines and yang lines?
The first question anyone studying the I Ching asks: why are there two kinds of lines, solid and broken? Many Chinese scholars have put forward hypotheses, but most are not entirely convincing.
The generative-organ theory: According to Guo Moruo, the yang line is a symbol of the phallus, the yin line a symbol of the vulva: a remnant of ancient fertility belief. From this came the notions of male and female, father and mother, yin and yang, firm and yielding. However, this explanation is heavily sexual and does not explain why a three-line structure is needed for a trigram.
The yarrow-stalk counting theory: Some hold that yin and yang lines originate from yarrow-stalk divination: using 50 yarrow stalks, through three transformations one obtains the numbers 36, 32, 28, 24; dividing by 4 gives 9, 8, 7, 6. Odd numbers (9, 7) are yang, even numbers (8, 6) are yin, and from this they are reduced to solid and broken lines. But as many researchers point out, number and image share only a resemblance and are not one and the same: yarrow-stalk divination uses numbers to divine, whereas the I Ching originated from images. Without the images of yin and yang lines there could be no Yi.
The oracle-bone numeral theory: Zhang Zhenglang, basing himself on groups of numerals on Shang dynasty oracle bones, held that the number 1 (the character for one) became the yang line and the number 6 (the character for six, written as /\ ) became the yin line. But Zhou Bakun's group refuted this: using the numbers 1, 5, 6, 7, 8 cannot explain why the I Ching has exactly 8 primary trigrams and 64 derived hexagrams: because mathematically, there are only 2^3 = 8 combinations of two kinds of lines when three lines are arranged, and 8^2 = 64 when two trigrams are stacked. Different numbers cannot produce such a consistent system.
A suggestion from Đông Sơn bronze drums
Another interesting direction comes from Vietnamese archaeology. On Đông Sơn bronze drums, people have found motifs of lines and dots on the sides of boats and on drum faces: these may be images of yin and yang lines. This suggests that the ancient Vietnamese used solid and broken line symbols very early, before the I Ching was widely spread in China. However, caution is needed: the connection between bronze drum patterns and Yi lines remains a hypothesis, with no direct evidence.
What is the philosophy of yin-yang and the eight trigrams?
Yin and yang: the two foundational forces
The philosophy of the I Ching revolves around the concept of yin and yang: two sides that are opposed yet complement each other: day and night, hot and cold, male and female, strong and weak. Yin and yang are not static but always transform: when yang reaches its extreme, yin is born; when yin reaches its extreme, yang is born. The interweaving of yin and yang gives rise to the five elements and to all things.
In the I Ching, yin and yang are represented by the yin line (--) and the yang line (-). Each trigram has three lines (single trigram) or six lines (hexagram). The order of the lines from bottom to top symbolizes the process of development from inner self to outer circumstance, from root to tip.
What are the eight trigrams?
From the two lines yin and yang, the ancients stacked three lines together, creating 2^3 = 8 combinations, called the eight trigrams. Each trigram has a name, a natural symbol and a philosophical meaning:
| Trigram | Symbol | Meaning |
|---|---|---|
| Qian (☰) | Heaven | Creation, strength |
| Kun (☷) | Earth | Receptivity, nurturing |
| Zhen (☳) | Thunder | Arousal, awakening |
| Xun (☴) | Wind | Penetration, spreading |
| Kan (☵) | Water | Danger, wisdom |
| Li (☲) | Fire | Clarity, brightness |
| Gen (☶) | Mountain | Stillness, separation |
| Dui (☱) | Lake | Joy, exchange |
The eight single trigrams move according to two great circles: the Earlier Heaven diagram (the diagram of before heaven) and the Later Heaven diagram (the diagram of after heaven). The Earlier Heaven diagram describes the state of the universe before human intervention, while the Later Heaven diagram reflects the flow of life in the phenomenal world. (Some documents mention a Middle Heaven diagram, but it is not widely known.)
What do the 64 hexagrams mean?
When two single trigrams are stacked on each other, we have 8 × 8 = 64 hexagrams, each consisting of six lines. Each hexagram is a specific situation in life, from great matters such as governing a country to small matters such as everyday conduct. The I Ching does not give absolute right or wrong answers but indicates the direction of development based on the interaction between the lines.
For example, the Qian hexagram (heaven) consists of six yang lines, symbolizing intense creative power, but the advice is to know humility and not to be overly strong. The Kun hexagram (earth) consists of six yin lines, exalting compliance and nurturing, but also requiring perseverance. The combination of yin and yang in each hexagram is read by commentators as subtle lessons, reflecting the dialectical outlook of the ancients.
How did the ancients cast a hexagram?
To have a hexagram to interpret, the ancients tossed three coins or used yarrow-stalk divination. Yarrow stalks are the ancient method, tied to the origin of yin and yang lines; tossing three coins is the later, popular way because it is compact and easy to do. Both aim to determine whether each line is yin or yang, and from there to build the hexagram. For details of how it is done, please see How to cast an I Ching hexagram: yarrow stalks, coins, numbers, time, or use the cast a hexagram tool if you want to practise right away.
What is special about the symbolism and language of the Yi?
What makes the I Ching a wondrous book is its symbolic language: with only two signs, yet with a many-valued function like a magic wand. Yin and yang lines are not merely drawings but contain an entire philosophical system about movement and transformation. Thanks to symbols, a student of the Yi can contemplate every matter from many angles, seeing the opposing side within a single whole.
The Great Treatise says "life upon life is called Yi" (ceaseless generation is called Yi), so the reader of the Yi exalts flexible conduct: nothing is immutable, everything transforms. When facing difficulty (an inauspicious hexagram), remember that difficulty will pass; when prospering (an auspicious hexagram), beware of decline. That is a philosophy of balanced living, harmony between yin and yang.
What does the I Ching mean in the context of Vietnamese culture?
There are hypotheses that the I Ching originated in Vietnam, based on the patterns on Đông Sơn bronze drums. However, this remains a contested question and needs much more archaeological and linguistic research. Whatever its origin, the I Ching has deeply influenced Vietnamese culture through fields such as traditional medicine, feng shui, martial arts, and philosophy of life. Vietnamese people have long used the Yi to choose days, select house directions, or interpret events in life.
