Three lines, eight figures
A trigram is a figure of three lines, each one either yang (solid) or yin (broken). With two options per line, there are exactly eight combinations, and those are the eight trigrams, 八卦. They're the building blocks of the 64 hexagrams: every hexagram is one trigram below (the lower trigram) and one above (the upper trigram). Eight times eight makes sixty-four.
Tradition credits the trigrams to Fu Xi, a mythic sage said to have drawn them after watching the sky, the earth and the animals. It's a legend, not history, but it gets one thing right: the trigrams are images of nature.
The eight, one by one
Lines are read from the bottom up.
- Heaven, 乾 Qián: three yang lines. Creative force, strength. In the family, the father.
- Earth, 坤 Kūn: three yin lines. Receptiveness, what holds and gives form. The mother.
- Thunder, 震 Zhèn: yang at the bottom, two yin above. Waking up, the movement that shakes things. The eldest son.
- Water, 坎 Kǎn: yang in the middle, between two yin. Danger, depth, what keeps flowing. The middle son.
- Mountain, 艮 Gèn: yang on top, two yin below. Stillness, limits, knowing when to stop. The youngest son.
- Wind, 巽 Xùn: yin at the bottom, two yang above. The gentle thing that gets in little by little, like wind or a tree's roots. The eldest daughter.
- Fire, 離 Lí: yin in the middle, between two yang. Clarity, light, what clings in order to burn. The middle daughter.
- Lake, 兌 Duì: yin on top, two yang below. Joy, exchange, words that are shared. The youngest daughter.
The Discussion of the Trigrams (說卦, one of the Ten Wings) sums up each one in a single word: 乾，健也。坤，順也。震，動也。巽，入也。坎，陷也。離，麗也。艮，止也。兌，說也。 That is: Heaven is strength; Earth, yielding; Thunder, movement; Wind, entering; Water, sinking in; Fire, clinging; Mountain, stopping; Lake, joy.
The logic of the family
The family isn't decoration. It follows a rule. Heaven and Earth are the parents. The sons are the trigrams with a single yang line among yin lines, and the daughters have a single yin line among yang lines. Where that odd line sits tells you the birth order: at the bottom, the eldest; in the middle, the middle child; on top, the youngest.
So Thunder, with its yang line at the bottom, is the eldest son, and Lake, with its yin line on top, is the youngest daughter. Once you know this rule, you can recognize any trigram without memorizing a chart.
The two arrangements
The trigrams are often drawn in a circle, one for each direction. There are two classical arrangements.
Earlier Heaven, which tradition credits to Fu Xi, sets opposites face to face: Heaven in the south and Earth in the north, Fire in the east and Water in the west, Thunder across from Wind, Mountain across from Lake. It's a picture of balance, of forces that offset each other.
Later Heaven, credited to King Wen, follows the cycle of the year and the day: Thunder in the east, where everything wakes in spring; Wind in the southeast; Fire in the south, at the height of summer; Earth in the southwest; Lake in the west, in autumn; Heaven in the northwest; Water in the north, in winter; and Mountain in the northeast, where one cycle ends and the next begins. It's a picture of movement, of how things follow one another.
The diagrams we know today spread mainly from the Song dynasty on, although the Later Heaven order is already described in the 說卦. The credits to Fu Xi and King Wen are traditional.
How they help in a reading
When you get a hexagram, looking at its two trigrams is one of the quickest ways into it. The lower one is often read as the inside: your attitude, or how the matter begins. The upper one is the outside: the surroundings, or where things open up. Water below Heaven doesn't feel like Heaven below Water, even though the pieces are the same.
Each trigram has its own page, with its images, its season and the hexagrams where it doubles. To see what their lines are made of, go on to Yin and Yang.