Si · Snake

Meaning

Si is the sixth Earthly Branch: the branch of the Snake, of the south-south-east, of the double hour from nine to eleven in the morning and of the fourth month of the Chinese year, which opens the summer. It is Fire, yin: the warmth that builds before noon, the heat stored in a stone in the sun. The Han historians read its name as 已 yǐ, already, finished: in the fourth month, Xu Shen wrote, yang has already come all the way out and yin has already gone into hiding, and the character, he added, is the shape of a snake.

It is read as insight, discretion and concentration, the Snake’s wisdom, a mind that observes before it moves and then moves precisely, and a warmth that is felt rather than shown. Si works quietly towards its aims and sees beneath the surface of things. Its difficulty is the heat it holds: intensity kept inside can turn to suspicion or to a grip that is too tight, and what is already finished can be hard to let go.

As one of the four branches that begin the seasons, with Yin, Shen and Hai, Si is where a phase is born: Metal is born here, as Geng is in the life stages, while Fire takes its strength. It holds three stems, Bing its main qi, Wu and Geng: the sun, the ground it warms and the metal that will come with autumn.

In practice

• In BaZi, Si holds Bing as its main qi, with Wu and Geng. It is the Prosperity of Bing and Wu, the Peak of Ding and Ji, the Birth of Geng, the Nobleman of Ren and Gui and the Academic star of Jia. A Si month, from Lixia, about 6 May, to Mangzhong, about 6 June, is the start of summer, when Fire takes the lead; Ulune’s climate view suggests Water for summer charts.
• Its relations: Si is in harmony with Shen, a pair that leans towards Water, though the same two branches also form a punishment and a destruction, a mixed bond the tradition reads as both close and demanding. It begins the Metal trine with You and Chou, and the summer trio with Wu and Wei. It clashes with Hai, harms Yin, and belongs to the “ungrateful” punishment with Yin and Shen.
• In Chinese astrology, Si is the Snake: 2025 was a Wood Snake year and 2037 will be a Fire Snake year.
• In Feng Shui, Si is the last mountain of the south-east, from 142.5° to 157.5°, a yang one for the Flying Stars.

Across traditions

• In Japan the branch is read mi, the snake; in Korea sa; in Vietnam Tỵ. China’s old spring festival of purification, Shangsi, takes its name from the branch: it was first held on the first Si day of the third month, later on the third day of that month, and it was for Shangsi that Wang Xizhi gathered his friends at the Orchid Pavilion in 353 and wrote the preface that became the most famous work of Chinese calligraphy.
• The Yi Jing’s sovereign hexagram for the Si month is the Creative (Qian, the 1st): six whole lines, yang at its fullest before the solstice turns it.
• The snake is an image of wisdom and renewal in many traditions, the serpent that sheds its skin, the staff of Asclepius; Western astrology has no snake among its signs; during the Si month the Sun crosses from Taurus into Gemini.

Origin and history

Si is one of the branch characters of the Shang oracle bones; Xu Shen’s Shuowen Jiezi (c. 100) already reads its shape as a snake, which may be why the Snake came to stand for it. The Huainanzi (139 BC) puts Si at the start of summer; Sima Qian explained it by yang that has come to its end, and Ban Gu wrote that things are at their fullness in Si. The festival of Shangsi, named after the branch, was later fixed on the third day of the third month, where it still falls.

BaZi’s classics count Si among the four places of birth, and read the meeting of Yin, Si and Shen, three branches that each begin a season, as the ungrateful punishment: three beginnings that pull in different directions. The Yuanhai Ziping of the Song dynasty and the San Ming Tong Hui of the Ming describe it, and Ulune reads it, as pressure to manage with clear agreements rather than as a fate.

How Ulune calculates it

Ulune numbers Si 5 among the branches. The Si month runs from the exact moment of Lixia, the Sun at 45°, to Mangzhong, the Sun at 75°; the Si hour is 09:00 to 11:00 on true solar time at the birthplace by default. In BaZi’s balance its hidden stems count 0.6 for Bing, 0.3 for Wu and 0.1 for Geng, twice in the month branch. Si and Shen show how relations can overlap: their places add up to 1, a harmony; they are of one punishment group; and Shen is yang and three places after Si, a destruction. Ulune names all three, in that order. For a year or day branch of the Hai, Mao and Wei trine, Si is the Travelling Horse.

Correspondences