Rotting Grass Transforms into Fireflies: The Philosophy of Metamorphosis and the Earth Virtue of Late Summer in the Great Heat
This article offers a deep reading of Great Heat (Dashu), the twelfth of the twenty-four solar terms, through the lenses of pre-Qin Confucian and Daoist philosophy, classical etymology, and astronomical phenology. It reveals the cosmic significance of the sun reaching ecliptic longitude 120°, when summer heat attains its zenith, and explores the Earth virtue of late summer, the metamorphosis of rotting grass into fireflies, and the hexagram Dun with its two rising yin lines — illuminating the ancient wisdom of reversal at the extreme and counterbalancing excess.
Chapter Ten: Yin-Yang and the Five Phases — Fire's Extreme Generating Water and the Five-Phase Regulation of Great Heat
I. The Yin-Yang Configuration of Great Heat: Yang at Its Extreme, Yin Is Born
Understanding Great Heat's yin-yang configuration requires starting from the Summer Solstice. The Book of Changes teaches: "At the Summer Solstice, a single yin is born." From the Solstice to Great Heat, yin energy has been quietly growing for about a month. In the Twelve Sovereign Hexagrams, the Solstice's fifth month is Gou (one yin born); Great Heat's sixth month is Dun (two yins growing) — yin has doubled.
Why does yin energy begin to grow at the very moment yang is at its strongest$9 This is the deepest dialectic of yin-yang theory. The Xici Zhuan says: "As the sun departs the moon arrives; as the moon departs the sun arrives; sun and moon push each other onward and brightness is born. As cold departs heat arrives; as heat departs cold arrives; cold and heat push each other onward and the year is completed." There is no absolute, eternal "yang," nor absolute, eternal "yin." Yang at its extreme must transform into yin; yin at its extreme must transform into yang.
The Most High wrote: "The ten thousand things carry yin on their backs and hold yang in their arms; the blending breath (chong qi) brings harmony" (Daodejing, Chapter 42). Even at Great Heat, the moment of yang's greatest intensity, yin has never been absent — it is only hidden behind yang ("carrying yin on its back"), awaiting the moment of yang's extreme to become manifest.
II. Fire Virtue at Its Zenith: South, Crimson, Flaring Upward
The Classic of Documents says: "Fire is called flaring upward" (huo yue yan shang). Heat and ascending — these are fire's two fundamental characteristics, expressed to their utmost at Great Heat.
Yet the zenith of Fire virtue is precisely the beginning of its decline. The Li (Fire) hexagram (䷝) has the image of "empty at the center" — two yang lines with a yin line between them. This "central emptiness" is deeply suggestive: the most blazing fire (Li) is actually "empty" (yin) at its core. This echoes the Most High's "great fullness seems empty."
III. Fire Generates Earth: Fire Virtue's Transformation into Earth Virtue
In the cycle of mutual generation, "Fire generates Earth." Great Heat's late summer is precisely the critical link in this transformation. Fire's blazing (the force of growth and expansion) must ultimately transform into Earth's nurturing (the force of ripening and consolidation). If Fire is the power of "growth," then Earth is the power of "transformation" — turning growth into fruition.
IV. Earth Generates Metal: Preparing Nurture for the Coming Harvest
After Fire generates Earth comes "Earth generates Metal." Earth virtue's transformative nurture ultimately converts into Metal virtue's gathering and contraction (autumn). Through the chain "Fire → Earth → Metal," Great Heat — though still midsummer — is already preparing for autumn's harvest.
This chain reveals Great Heat's pivotal position in the year's Five-Phase cycle. It is simultaneously the endpoint of Fire virtue (fire's extreme), the zenith of Earth virtue (earth's flourishing), and the prelude to Metal virtue (ripening in preparation for harvest). Great Heat embodies the critical juncture of three virtues at once — Fire about to retreat, Earth at its height, Metal about to arrive.
V. Five-Phase Regulation: The Dynamic Balance of Mutual Generation and Restraint
The essence of Five-Phase theory lies not in any single relationship of generation or restraint, but in the dynamic balance constituted by their interplay — this is "regulation" (zhihua).
At Great Heat we observe: Fire is at its extreme (excess), and so Water rises to restrain it ("Water overcomes Fire" — great rains descend, counterbalancing excess); simultaneously, Fire generates Earth (Fire virtue transforms into Earth's nurture — moist earth and sultry heat), and Earth generates Metal (nurture prepares for autumn harvest). Within a single solar term, mutual generation (Fire → Earth → Metal) and mutual restraint (Water overcomes Fire) play out together, jointly maintaining the dynamic balance of heaven-earth energy.
The insight this "regulation" offers is profoundly relevant: any healthy system requires both "generating" forces (support, promotion, growth) and "restraining" forces (regulation, adjustment, balance). Unchecked "generation" (as when Fire alone rages) leads to runaway disaster; timely "restraint" (as when great rains check fire) restores equilibrium.