Si

The oracle glyph of Si resembles a fetus, or a coiled snake. The Shuowen: "Si — in the fourth month Yang qi is fully out, Yin qi fully hidden; all things appear, their patterns complete." Si shares a root with yi, "already": the sense of a thing accomplished.

Matched to the Snake — coiled, quick, reborn through shed skin — its hidden anatomy reads like a volcano: Bing Fire erupting (main qi), Wu Earth as the cone (middle), Geng Metal as ore veins inside (residual). Fire on the surface; a smelter underneath.

By order Si is a Yin branch, but its main hidden stem is Yang Fire Bing — "Yin in body, Yang in function": compute it as Bing. It is the Lu throne of both Bing and Wu Earth, and — more remarkably — the birth stage of Metal: the Si-You-Chou frame takes Si as its birth corner.

Metal born inside Fire is Si's deepest mechanism: in the fourth month, at Fire's crest, the next cycle's contraction is already seeded. Of all the foreshadowings built into the five-element cycle, this is the most elegant.

Si-Shen is the six-combination that transforms into Water — Fire and Metal producing Water, the least intuitive pair of the twelve, and simultaneously a punishment (Si and Shen both combine and punish: love and grievance braided). Si-You-Chou forms the Metal frame from Si's cradle. Si versus Hai clashes fire and water at the birth-stage corners — journeys, relocations, second-guessing.

The Yin-Si-Shen punishment trio pivots on Si. Its relation web holds clash, combination and punishment all at once, mutually entangled — when a chart's Si is triggered, fortune and misfortune tend to arrive as two faces of one event.

In the pillars Si computes as Bing Fire: Fire Day Masters find their throne, Wood finds its bloom, and Metal meets Officer stars and its own birth stage in the same house — a Geng Day Master sitting on Si poses one of the finer judgment calls in the craft.

The hidden Geng also makes Si Metal's home port: for a Metal-weak chart, one Si delivers both warmth and birthplace. Like Yin, Si works multiple posts — before judging, identify which tenant answered the door: Bing, Wu or Geng.

The Si hour (9–11 a.m.) was "corner-of-noon watch." The Shangsi festival — originally the first Si day of the third month, later fixed on the third day — was the ancient riverside purification rite: Wang Xizhi's Orchid Pavilion Preface records precisely such a Shangsi gathering.

The Si month opens with Li Xia, the door into summer. The Snake year's courtesy title "little dragon," and sundry homophone taboos, are this character's echoes in folk life.