Week 4 Session: Eight from Three — Constructing the Bagua

How do three lines generate a complete symbol set?

15 March 2027

The question

Two lines gave four bigrams. What does the same doubling rule give you at three lines?

What this builds on

Week 3 established combination as the system’s generative mechanism. This week completes it: three lines exhaust the combination rule at eight trigrams, the full Bagua (八卦).

Eight trigrams, eight natural images

Three binary positions give eight combinations — the same arithmetic as week 3, one more line deep. Each of the eight has a name and, per the Shuogua zhuan (說卦傳, one of the Ten Wings), an attributed natural image and family role: Qian ☰ (three yang lines) is Heaven, the father; Kun ☷ (three yin lines) is Earth, the mother; and the other six — Zhen ☳, Kan ☵, Gen ☶, Xun ☴, Li ☲, Dui ☱ — are read as Thunder, Water, Mountain, Wind, Fire, and Lake respectively, each assigned a son’s or daughter’s role depending on which single line differs from all-yin or all-yang and where it sits in the stack.

  1. Qian — Heaven, the father
  2. Kun — Earth, the mother
  3. Zhen — Thunder
  4. Kan — Water
  5. Gen — Mountain
  6. Xun — Wind
  7. Li — Fire
  8. Dui — Lake
All eight trigrams (Bagua, 八卦), each built from three stacked lines. Names and natural images are the Shuogua zhuan's attributions (week 4).

That correlational content — name, image, family role — is attested to this specific text; it is a property of the trigram itself, independent of how the eight trigrams get arranged into a larger order. Two different arrangements of these same eight objects are still to come (weeks 6–7) — this week is deliberately only about what each trigram is, not where it sits.

What you should be able to do after this week

Construct all eight trigrams directly from the line rule, then meet the Shuogua zhuan’s attributed name, natural image, and family role for each. Next week asks a different question about these same eight objects: how do they relate to each other, before any arrangement is imposed?

The spec

What you bring to the session. Written so a reader can tell whether it has been met without asking you.

Teaching team