Yin and yang lines in a hexagram

Two kinds of stroke: unbroken and broken

Every hexagram in the Zhou Yi is a stack of six strokes, and a stroke comes in only two forms. An unbroken stroke is a yang line; a stroke broken in the middle is a yin line. The word for one stroke is line (爻, pronounced yáo).

Open the full-size diagram

Sketch: the six lines of Jiji from the bottom up are yang, yin, yang, yin, yang, yin. A structure diagram, not a reading.

The figure shows Jiji (既济). Counting from the bottom, lines 1, 3 and 5 are yang and lines 2, 4 and 6 are yin. Because the two forms alternate, each line's place and form can be read off separately.

What the Great Commentary says a line is

A line is more than a drawing convention. The Great Commentary (Xi Ci, 系辞) mentions it in several places, and each time the vocabulary is about change and movement.

The upper part of the Xi Ci says: "The Tuan (彖) speaks of the images; the lines speak of change." The lower part says: "The lines imitate the movements under heaven." The verb there means to model oneself on something, so a line is described as copying the motions of the world.

Because the Way has change and movement, it is called a line; lines have grades.

This sentence ties the word line to movement and then says lines have "grades", which commentators mostly take to mean different ranks. That points to the next section: the six lines are not laid side by side, each one rests on the one below.

Reading from the bottom: place first, then form

Count the six lines upward. The lowest is called Initial (初), the highest Top (上), and the four between are Two, Three, Four and Five. These are the names the Zhou Yi itself uses.

Most hexagrams become a different hexagram when read upside down, as Jiji becomes Weiji. Only eight are symmetric end to end and read the same either way: Qian (乾), Kun (坤), Yi (颐), Daguo (大过), Kan (坎), Li (离), Zhongfu (中孚) and Xiaoguo (小过). The table writes the six lines of Jiji out by place:

The six lines intermingle, each answering only to its own time and thing. The initial line is hard to know, the top line is easy to know: they are root and branch.

The passage sets the Initial line and the Top line side by side as root and branch. So within the text itself the six lines form an ordered series with a start and an end.

1. 1

   Write the places

   Number the page from 1 to 6, bottom to top: Initial at the foot, Top at the head.

2. 2

   Fill in the forms

   Give each place one entry only, yang (unbroken) or yin (broken).

3. 3

   Read it back

   Recite the forms in order from 1 to 6, then compare with the drawing from its bottom up.

Stacking line by line: why sixty-four

Each place has two choices, so one line has 2 forms. Put a second line on top and two lines give 2 × 2 = 4 patterns. Every extra line doubles the total.

The Changes have the Supreme Ultimate; it gives rise to the two modes; the two modes give rise to the four images; the four images give rise to the eight trigrams.

The sentence names two modes, four images and eight trigrams in turn. Later commentators often match these to the 2 patterns of one line, the 4 of two lines and the 8 of three lines. The text stops at the eight trigrams; three more doublings give 16, 32 and 64, which is the same procedure carried on. The lower part adds: "When the eight trigrams stand in rows, the images are within them; when they are doubled, the lines are within them." Doubling the trigrams into six lines is exactly this step.

Grouping the sixty-four by how many yang lines they hold gives a second count:

Only one hexagram has six yin lines, Kun (坤), and only one has six yang lines, Qian (乾). A second way of reaching 64, by pairing a trigram with a trigram (8 × 8), is set out in the sixty-four hexagrams.

Same line, new place, new hexagram

Hexagrams with the same forms and the same counts are still different hexagrams when the places differ. Exactly 6 hexagrams contain a single yang line, one for each place.

Fu and Bo each have one yang line and five yin lines. The only difference is whether that yang line stands in place 1 or place 6. To read further you need the name and meaning of each place; those are covered in line positions, from Initial to Top.