Chapter Seven: "Therefore These Are Called Yao" — The Naming and Essence of the Line

I. The Etymology of Yao

Yao (爻, yao) — no confirmed instance of the character has been found in oracle-bone script. But Xu Shen's Shuowen Jiezi glosses it: "Yao means 'crossing.' It depicts the interlocking heads of the six yao of the Yi." Duan Yucai annotates: "Yao means 'to model' (xiao) — to model the movements of all under heaven."

The character yao consists of two "X" (crossing) marks stacked vertically. This form quite directly conveys the meaning of "crossing" — upper and lower intersect, yin and yang interlace.

From an etymological standpoint, yao is closely related in sound and meaning to xiao (效, to model) and jiao (交, to cross/interact). In Old Chinese phonology, yao belongs to the xiao rhyme group with a velar initial, xiao (效) likewise to the xiao rhyme group with a velar initial, and jiao (交) to the xiao rhyme group with a velar initial — all three share the same rhyme category with closely related initials, strongly suggesting a common etymological origin.

Thus the character yao itself contains three layers of meaning:

1. Crossing — intersection, interaction: the interlaced arrangement of yin and yang lines.
2. Modeling — emulation, patterning: modeling the patterns of the world's movements.
3. Change — transformation, alternation: the changing of a line (changing yao) is the basic unit of hexagram transformation.

II. Why Are There Six Lines$30

A hexagram has six lines. Why six rather than five, seven, or eight$31

This question has long been debated. The Xi Ci Xia Zhuan offers a classic explanation:

"As a book, the Yi is vast and complete. It contains the Way of Heaven, the Way of Humanity, and the Way of Earth. It doubles the Three Powers — therefore six. Six is nothing other than the Way of the Three Powers."

The "Three Powers" (san cai) — heaven, earth, and humanity. "Doubling the Three Powers" — each power has both a yin and a yang aspect, so three times two equals six.

The first and second lines represent the "Way of Earth" (yielding and firm); the third and fourth lines represent the "Way of Humanity" (benevolence and rightness); the fifth and sixth lines represent the "Way of Heaven" (yin and yang).

This explanation is elegant, but we may press further: why "double the Three Powers"$32 Why not "triple the Three Powers" to get nine$33

The answer likely resides in the fundamentality of yin-yang thinking — all things can ultimately be resolved into yin and yang aspects. Heaven has yin and yang (moon and sun), earth has yin and yang (mountain and marsh), humanity has yin and yang (female and male). "Doubling" is not a mathematical operation but reflects a fundamental ontological conviction: every level of the cosmos is yin-yang dyadic.

The six-line arrangement enables a hexagram to fully express the yin-yang changes at each of the three levels — heaven, earth, and humanity — and their mutual interactions. This constitutes a complete model of "the movements of all under heaven." The auspiciousness or inauspiciousness of each line is intimately related to its "position" (wei) within this model and its "relationships" with the other lines (correspondence, adjacency, riding, supporting). This returns us to "observing where they converge and connect" — the convergence and connection among lines determine each line's destiny.

III. The Essentially Dynamic Nature of Yao

Xiang is a static, structural expression; yao is a dynamic, processual expression. This distinction is confirmed in the actual operation of hexagram casting.

When we use the milfoil method to cast a hexagram, we obtain a "primary hexagram" and one or more "changing lines." The overall image of the primary hexagram is xiang; the specific changing lines are yao. The position of the changing line marks the critical node where change is currently occurring in the present situation.

For example, suppose we obtain the Tai hexagram (Earth over Heaven, ☷☰), with Nine in the Third as the changing line. The xiang tells us: the current situation is one of mutual communication between heaven and earth, harmonious accord of yin and yang — an image of peace and flourishing. The changing line (Nine in the Third) tells us: within this overall picture of peace, change is occurring at the third position — specifically, yang energy is rising from the highest position in the lower trigram and about to enter the domain of the upper trigram. The line statement for Nine in the Third reads: "No plain without a slope, no going without a return. Persevere through difficulty — no fault." This means: there is no road that stays level forever, no journey that goes only outward — within the peace already lie the seeds of reversal.

This is the subtlety of yao: it tells you not only the current configuration (xiang), but also where and how that configuration is changing (yao), and whether the trend of that change is auspicious or inauspicious (the statement).