Yin and Yang in Equal Measure: The Way of Central Harmony and the Equilibrium of Day and Night at the Spring Equinox
This article offers a multi-dimensional exploration of the Spring Equinox (Chunfen) among the Twenty-Four Solar Terms, drawing on pre-Qin Confucian and Daoist philosophy, the original meanings of Chinese characters, and astronomical phenomena. By analyzing the character 'fen' (divide/equalize), the sun's alignment with the equator, and seasonal signs such as the return of swallows and the onset of thunder, it reveals the profound wisdom of 'central harmony' and the unity of Heaven and humanity embedded in the equinox's equal days and nights.
Chapter Seven: The Book of Changes and the Spring Equinox -- The Thunder-over-Heaven Image of the Dazhuang Hexagram
I. Dazhuang in the Twelve Sovereign Hexagrams
The Book of Changes is the encyclopedia of pre-Qin thought, containing the most profound insights into the laws governing cosmic operation. Though the Book of Changes does not directly discuss solar terms, its hexagram system shares deep correspondences with the succession of the four seasons, concentrated in the "twelve sovereign hexagrams" (shi'er xiaoxi gua).
The twelve sovereign hexagrams pair twelve hexagrams with twelve months, displaying the process of yin-yang waxing and waning over the year:
Eleventh month: Fu (Return) -- one yang is born. Twelfth month: Lin (Approach) -- two yangs grow. First month: Tai (Peace) -- three yangs open up. Second month: Dazhuang (Great Vigor) -- four yangs are robust. Third month: Guai (Breakthrough) -- five yangs displace yin. Fourth month: Qian (Heaven) -- six yangs, pure yang. Thereafter yin begins to stir: fifth month: Gou (Encounter) -- one yin is born. Sixth month: Dun (Retreat) -- two yins grow. Seventh month: Pi (Standstill) -- three yins, three yangs. Eighth month: Guan (Contemplation) -- four yins are strong. Ninth month: Bo (Splitting Apart) -- five yins strip yang away. Tenth month: Kun (Earth) -- six yins, pure yin.
The second month (the month of mao), in which the Spring Equinox falls, corresponds to Dazhuang (Great Vigor). The image of Dazhuang is Qian (Heaven) below and Zhen (Thunder) above -- "Thunder over Heaven, Great Vigor." In terms of individual lines, Dazhuang has four yang lines below and two yin lines above -- a "four-yang, two-yin" hexagram.
This "four-yang, two-yin" line configuration corresponds strikingly with the astronomical reality of the Spring Equinox. In the yang-growth sequence of the twelve sovereign hexagrams -- Fu (one yang), Lin (two yangs), Tai (three yangs), Dazhuang (four yangs) -- by Dazhuang, the yang lines have increased to four, surpassing the yin lines (two yins). This exactly corresponds to the turning point around the Spring Equinox when yang surpasses yin: before the equinox, yin still predominates; after it, yang grows daily stronger. Dazhuang's "four-yang, two-yin" configuration -- yang having passed the halfway mark and still waxing -- is the hexagrammatic portrait of the vigorous, ascendant yang energy at the time of the Spring Equinox.
II. The Name "Great Vigor": A Paean to Yang's Robust Strength
The hexagram name "Dazhuang" (Great Vigor) itself is profoundly meaningful. The "Commentary on the Judgment" (Tuan zhuan) says: "Great Vigor: the great is vigorous. Firmness in motion, therefore vigor. Great Vigor is beneficial when upright; the great is the correct. When correct and great, the true nature of Heaven and Earth can be seen."
Let us savor each line. "Great Vigor: the great is vigorous" -- Great Vigor means the "great" (yang, the firm and strong) is vigorous and robust. "Firmness in motion, therefore vigor" -- firm energy combined with motion (Qian below is firm, Zhen above is motion), hence vigor. This is a portrait of the energy of Heaven and Earth at the Spring Equinox: yang's firm energy (Qian), under the impetus of spring thunder's stirring (Zhen), swells to robustness.
"Great Vigor is beneficial when upright; the great is the correct" -- this line is especially pivotal. It links the robust vigor of Dazhuang with "correctness" (zheng -- centrality, the upright Way). Though yang energy is vigorous, it is not blind inflation or manic surging, but a vigor that accords with "correctness." This fits perfectly with the spirit of the Spring Equinox: after the equinox, though yang surpasses yin and waxes daily, this vigor is restrained and in accord with the upright Way -- it is "the great is the correct," not the overblown yang of the Summer Solstice teetering on the brink of decline.
"When correct and great, the true nature of Heaven and Earth can be seen" -- correct and great, and the true sentiments of Heaven and Earth are revealed. What a profound statement! The "true nature" of Heaven and Earth is revealed in this "correct greatness." At the Spring Equinox, when yang is vigorously growing yet accords with centrality, the essential character of Heaven and Earth -- ceaselessly generating, gloriously flourishing -- is most fully revealed.
III. "Do Not Tread Where It Is Not Proper": Restraint Amid Vigor
The "Image Commentary" (Xiang zhuan) of Dazhuang offers an unexpected yet profoundly insightful admonition: "Thunder above Heaven: Great Vigor. The noble person thereby does not tread where it is not proper (fei li fu lu)."
This admonition may seem puzzling at first: Dazhuang is plainly a hexagram of robust yang strength, symbolizing power at its peak -- so why does the Image Commentary urge the noble person to "not tread where it is not proper," emphasizing restraint and adherence to propriety$6
Herein lies the Book of Changes' most profound dialectical wisdom. The more robust one's strength, the greater the need for restraint; the more yang energy is at its peak, the more one must hold to propriety and self-discipline. Why$7 Because latent within robustness is the danger of losing control. Once strength escapes restraint, "correct greatness" degenerates into "violence," and the force of generation becomes a force of destruction. The spirit of Dazhuang does not encourage bullying the weak or indulging in power, but teaches that when one possesses great strength, one should use "propriety" (li) to regulate and restrain it, keeping it always on the path of "correctness."
This once again perfectly accords with the spirit of the Spring Equinox. After the equinox, yang energy is robust and all things flourish. But this very robustness requires the restraint of "central harmony" -- as the Doctrine of the Mean says, "when aroused and all attaining their due measure, this is called harmony." The "arousal" (robustness) of yang must "attain its measure" (be proper, be measured) to achieve "harmony" and enable all things to grow in good order. Dazhuang's admonition to "not tread where it is not proper" reminds people at the Spring Equinox: the greater the power, the more one must guard the center, guard propriety, guard correctness.
IV. Thunder Above Heaven: Dazhuang and the Phenological Resonance of the Spring Equinox
The image of "thunder above Heaven" in Dazhuang also directly and vividly corresponds to the phenological signs of the Spring Equinox.
As discussed in the Monthly Ordinances' account of mid-spring: "In this month, day and night are equal; thunder begins to sound; lightning first appears." At the Spring Equinox, thunder begins to rumble and lightning begins to flash. And Dazhuang's hexagram image -- Qian (Heaven) below, Zhen (Thunder) above -- is precisely "thunder above Heaven": the scene of spring thunder resounding across the sky!
This correspondence between hexagram image and phenological sign is no coincidence. The hexagram images of the Book of Changes were the ancients' highly abstract generalizations of the patterns governing the operation of all things. Dazhuang was assigned to the second month containing the Spring Equinox precisely because its image (thunder above Heaven, yang's robust vigor) best summarizes the atmospheric condition of the Spring Equinox -- spring thunder rumbles, yang is robust, and all things revive vigorously under the impetus of the thunder.
Thunder holds a supremely special significance in the Book of Changes. Zhen (Thunder) is its image, and the Shuogua (Discussion of the Trigrams) says: "The sovereign comes forth in Zhen." The sovereign (the driving force of cosmic generation) sets out from the Zhen trigram. Zhen corresponds to the east and to spring, representing the initial stirring of yang and the beginning of all things' generation. Dazhuang, with Zhen above and Qian below, is the further unfolding of "the sovereign comes forth in Zhen" -- yang has not only stirred but grown robust; thunder not only begins to sound but resounds across the sky. The "thunder begins to sound" at the Spring Equinox is the celestial manifestation of "the sovereign coming forth in Zhen" and yang's robust vigor.