Gui

Gui is the tenth and last of the Heavenly Stems (tiangan). Its element is Water and its polarity is yin, so Gui is glossed as yin Water, likened in tradition to rain, dew, or mist, gentle and pervasive where the yang Water of Ren is the sea. As the final stem it pairs with the twelve Earthly Branches to complete the pattern of the sexagenary cycle of sixty; after Gui the count of stems returns to Jia. Each of the five phases appears among the ten stems once as yang and once as yin, and Gui carries the yin aspect of Water that closes the round. These are the conventions of the Chinese calendrical and cosmological tradition, drawn on in the almanac and in the four-pillars art of fate calculation.

Gui is the tenth and final Heavenly Stem, paired with Ren under the Water phase but carrying the Yin polarity, likened to rain, mist or a quiet spring rather than Ren's ocean, gentle and pervasive rather than forceful. As an even-numbered stem, Gui combines only with the six Yin Earthly Branches, Ox, Rabbit, Snake, Goat, Rooster and Pig, closing out the sixty-term sexagenary cycle before it returns to Jia at position one. Because ten stems and twelve branches share a lowest common multiple of sixty, a complete Jia-to-Gui, Zi-to-Hai cycle takes sixty years, months, days or hours to repeat exactly, which is why traditional East Asian reckoning treats sixty years as a full cycle of a human life, marked in some communities by a huanjia or sixtieth-birthday celebration. In four pillars (BaZi) astrology a Gui day master is read as intuitive, adaptable and reflective, the most yielding of the ten stems.

Every stem has a partner among the other nine, and the five pairings, called the combinations of the heavenly stems, are fixed: each stem combines with the one five places away from it. Gui pairs with Wu, and the tradition holds that a combined pair takes on a phase of its own distinct from either stem's native phase. The pairing is used in almanac work and in fate calculation, where a combination in a chart is read as a binding between the two positions that carry it.

The ten stems are older than the sexagenary cycle they now form half of. On the Shang oracle bones of the second millennium BCE they name the ten days of the xun, the Shang week, and Shang kings are known to history by posthumous names built on them, so a stem was a unit of the working calendar before it was a term of cosmological art. The five-phase and yin-yang readings attached to the stems are later, systematised under the Han, and the atlas records the two layers as two layers.

Gui is yin Water, the tenth and last of the stems, conventionally the mist, the dew or the small rain against the ocean of Ren. Its position at the end of the ten gives it a role in the arithmetic of the sexagenary cycle: since sixty is the least common multiple of ten and twelve, the tenth stem meets the twelfth branch only once in sixty, at the close of the whole cycle.

The stem's own attributes here are Water and yin polarity. Those two facts fix its place in the run of ten, since the stems proceed through the five phases in generation order taking the yang member first and the yin member second, and they fix how it is read wherever it appears, in the year, the month, the day or the double hour of a Four Pillars chart.

Sources Chinese Mathematical Astrology: Reaching Out to the StarsHo Peng Yoke with The Chinese Sexagenary Cycle and the Ritual Origins of the CalendarAdam Smith