Trigram 兌 — Lake 兌 (Duì)

兌 (Duì) is the trigram of two yang lines below with one yin line on top — a solid base capped by an open, broken line. Its image is the Lake (澤), a body of water enclosed by earth, with a smooth surface that reflects the sky. The character of 兌 is joy that comes from openness: the lake holds and gives back, it does not rush like a river or hide like a well.

Among the eight trigrams, 兌 is the “Youngest Daughter.” The single yin at the top, sitting over two yang, is read as a young face above two firm legs — the easy openness of someone who has not yet been hardened by the world. The Shuogua attributes to it the mouth and tongue: 兌 is the trigram of speech, exchange, and the pleasure that comes from communicating.

The classical phrase from hexagram #58 (where 兌 doubles itself) is 麗澤，兌，君子以朋友講習 — “Two lakes resting on one another; thus the noble person joins with friends for discussion and practice.” The mode of 兌 is reciprocal: it gives and receives, and the joy is in the exchange itself.

兌 (Duì) is built from three horizontal lines, each either yang (solid, ⚊) or yin (broken, ⚋). The order in which the lines appear from bottom to top is what gives the trigram its character. For 兌, the configuration is:

The classical source for the meanings of the eight trigrams is the 說卦傳 (Shuogua Zhuan, “Discussion of the Trigrams”), one of the Ten Wings (十翼) appended to the Zhou Yi. The Shuogua catalogues the natural phenomena, body parts, animals, and human types attributed to each trigram. Below is the canonical Shuogua passage for 兌:

The Shuogua attributions are not arbitrary — they are read as a coherent extension of the trigram’s essential character. Where the trigram is, the things on the list belong: Lake as joyous, open extends to the mouth (the body part it governs), the sheep (its representative animal), and the west (its quadrant in the Post-Heaven Bagua). Each of these is a different lens onto the same archetypal pattern.

In a hexagram reading, knowing the Shuogua attributions lets you translate an abstract line pattern into concrete imagery. If the upper trigram of your hexagram is 兌, then the question what is above the situation can be answered with any of these images, depending on which fits the question you are asking.

兌 appears as the upper trigram in eight of the 64 hexagrams — one for each possible lower trigram. When 兌 is on top, its quality (joyous, open) describes the outer face of the situation: what is visible, what is publicly happening, the surface configuration. The lower trigram in each pairing modifies that outer face with the inner ground from which it emerges.

兌 appears as the lower trigram in eight of the 64 hexagrams. When 兌 is below, its quality describes the inner ground of the situation: the foundation, the disposition of the person inside the hexagram, the energy from which the upper trigram’s outer expression rises.

Eight of the 64 hexagrams are formed by doubling a single trigram — placing the same trigram both above and below itself. These are sometimes called the eight “pure” or “doubled” hexagrams, and they occupy a special structural place in the system: each one is the maximal expression of a single trigram’s nature, undiluted by any contrasting force.

For 兌, the doubled hexagram is hexagram #58: 兌 Duì — The Joyous (Lake). Lake on lake — joy that nourishes through fellowship. The deep joy of practicing together with friends; the danger of joy that seduces or seeks praise. If you cast this hexagram, the time-quality of Lake (joyous, open) is operating at its full strength, with no admixture from any other trigram.

The eight trigrams are arranged in two distinct circular sequences in classical Chinese cosmology: the Pre-Heaven Bagua (先天八卦, attributed to the legendary Fu Xi 伏羲) and the Post-Heaven Bagua (後天八卦, attributed to King Wen 文王). The two diagrams place the trigrams in different positions because they are reading different things.

The Pre-Heaven sequence is an ideal, time-out-of-time arrangement that pairs the trigrams as polar opposites: 乾 opposite 坤, 離 opposite 坎, 震 opposite 巽, 艮 opposite 兌. It describes the trigrams in their archetypal relations, before any seasonal or geographical specialisation. 兌 sits in the Southeast of the Pre-Heaven Bagua.

The Post-Heaven sequence is the arrangement that practitioners actually use in BaZi, Feng Shui, and the I Ching. It maps the eight trigrams onto the seasonal year: 兌 sits in the West of the Post-Heaven Bagua, corresponding to mid-autumn. This is the position you use when reading the trigram’s active influence on the world.

The two sequences are not in conflict. Pre-Heaven describes what Lake is; Post-Heaven describes when and where Lake acts. Classical practitioners hold both diagrams in mind and switch between them depending on the question.

In the Five-Element (五行) system that overlays the I Ching with BaZi and Feng Shui, 兌 is classified as Metal (金). This is the same Five-Element classification used to read seasonal energies, organ correspondences, and the elemental relations between two BaZi day masters. Within the I Ching itself, 兌 carries the following classical correspondences:

• Body part: Mouth (the part of the human body that the trigram governs in classical Chinese medicine and Yi medicine)
• Internal organ: Lungs (the organ in TCM that resonates with the trigram’s element and direction)
• Representative animal: Sheep (the animal whose nature embodies the trigram’s archetypal motion)
• Family member: Youngest Daughter (the position in the eight-trigram family, with 乾 as Father and 坤 as Mother and the other six trigrams as their three pairs of sons and daughters)
• Season: Mid-autumn (the time of year when the trigram’s energy is dominant in the Post-Heaven Bagua)

These correspondences are how a single trigram — an abstract three-line figure — becomes useful across multiple traditions. The same 兌 that you cast in an I Ching reading is the 兌 that maps to a direction in your Feng Shui chart, an organ in your TCM diagnosis, and an element in your BaZi pillars.

In contemporary practice, 兌 (Lake) is most useful as a diagnostic lens: when you find this trigram in a hexagram you have cast, the question becomes where in this situation is the quality of joyous, open acting? If it is the upper trigram, the surface of the situation has that quality. If it is the lower, the inner disposition does. If it appears in the nuclear hexagram (互卦), the structural undercurrent does.

兌 is also a useful frame for non-divinatory work. In coaching, strategy, and decision-making, asking “is this a moment of joyous, open?” gives you a classical test for whether the configuration you are facing matches the time-quality the trigram describes. If it does, the hexagrams in which 兌 appears as the upper trigram (such as #17 Following, #28 Preponderance of the Great, #31 Influence (Wooing)) are worth reading even without a formal cast.

For a personal reading that integrates the trigrams with your BaZi (Four Pillars) chart, 兌 layers onto your day master and current luck pillar to show how this archetypal force is acting on you specifically — the same trigram lands very differently on a Metal-friendly chart than on one where Metal is unwelcome.