Week 2 Session: One Splits into Two — Taiji and the Yin-Yang Line

What is the smallest visual distinction that can carry meaning?

1 March 2027

The question#

What is the smallest mark that can carry a distinction — and what happens when you commit to exactly two possible values for it?

What this builds on#

Week 1 asked what a change-representing sign system needs. This week introduces the smallest such unit: a single line, broken or unbroken.

The line, and the sequence it starts#

Draw one unbroken line and you have yang (陽); break it in the middle and you have yin (陰). That is the entire alphabet this notation starts from: one mark, two states, nothing in between.

Committing to exactly two values, no more, is what makes later stages of the system combinatorial rather than descriptive — week 3 asks what happens when you stack a second line.

The Xici (繫辭, one of the Ten Wings commentaries appended to the Zhouyi) gives a documented generative sequence for how the rest of the system is supposed to unfold: Taiji (太極) → Liangyi (兩儀, “the Two Modes” — yin and yang) → Sixiang (四象, “the Four Images”) → Bagua (八卦, the Eight Trigrams). That sequence is directly textually attested; what Taiji itself names is less settled. Scholarship renders it variously as “Great Ultimate” or “Supreme Polarity,” and this course does not adopt one fixed gloss — later weeks meet two very different things called “Taijitu” (a diagram of Taiji) that are historically separate images (week 10), which is reason enough to keep Taiji itself as a term in a sequence, not a settled picture yet.

It is tempting, on meeting a two-valued system, to reach immediately for binary digits as an equivalent. Resist that for now: a structural comparison (two values, combined by a rule) is fair game and useful; a historical connection between this notation and modern computing is a specific, documented, much narrower claim that the course examines directly in week 11 — and the popular version of that claim overstates what is actually known.

What you should be able to do after this week#

The Xici gives a documented generative sequence: Taiji → Liangyi (the two lines) → Sixiang → Bagua. This week keeps close to that sequence rather than treating Taiji as one settled cosmological idea — later interpretations (Zhou Dunyi’s diagram in week 10, popular “yin-yang symbol” readings) are separate objects of study, covered on their own terms later, not folded into this week’s definition. Next week takes the second step in the sequence: combining two lines.