What is saju
Four pillars, eight characters
Saju (사주, 四柱) is the Korean name for a system whose literal translation is "four pillars." In China it is known as BaZi (八字, "eight characters"). It reads a person from the moment of birth — from year, month, day, and hour.
Each of the four pillars consists of two characters: a heavenly stem (天干) and an earthly branch (地支). There are ten heavenly stems, five elements (wood, fire, earth, metal, water) in yin/yang polarity. There are twelve earthly branches; they correspond to the animals of the Chinese calendar, but they are not the "month signs" of Western astrology. Four pillars, two characters each, give eight characters per chart — hence the Chinese name.
The number of possible configurations: the day pillar has sixty variants, the hour pillar twelve variants for any given day. Combined with year and month, that yields over half a million unique pillar patterns. Once you add the interpretive layers — sipseong (relationships), gyeokguk (structures), dae-un (time cycles) — the count of possible readings climbs into the tens of millions.
Saju does not read from stars. It reads from the motion of the sun, from the solar calendar, from the proportions of elements present at the moment of birth.
Four dimensions of life
Each pillar corresponds to one dimension of life, but all four operate together on a single chart.
The year pillar (年柱) describes family, origin, and social image (how you are seen from the outside). In classical interpretation it also covers the first thirty years of life: what you inherited before you began choosing consciously.
The month pillar (月柱) describes environment, work, relationships with parents, and the third and fourth decades of life. It is the climate in which you grow into adulthood. In classical schools, the month pillar also determines the strength of the Day Master — whether the element of your core identity is reinforced by the season of birth, weakened, or neutral.
The day pillar (日柱) is central. The heavenly stem of this pillar, the Day Master, is the core of identity. It is who you are when no one is watching. All other elements of the chart are interpreted in relation to the Day Master: what reinforces it, what weakens it, what produces it, what controls it. Shifting the analytical center to the day pillar is Xu Ziping's innovation from the Song dynasty (960–1279). Earlier Tang schools used the year pillar as the primary axis.
The hour pillar (時柱) describes children, legacy, the second half of life, intimacy. The most subtle dimensions of a person. This pillar shifts every two hours of true solar time, and a difference of a few minutes near a boundary can change the interpretation. The hour pillar is optional in the sense that the other three still give a solid chart; if you know it, it adds a fourth dimension.
These four pillars are like four views of the same person from different distances: family, environment, self, legacy. Saju does not treat them as separate categories, but as overlapping layers of one life.
Where saju comes from
The system's oldest layer is the sixty-cycle calendar (ganzhi) from the Shang dynasty: ten heavenly stems crossed with twelve earthly branches. Their lowest common multiple is sixty; each combination repeats every sixty units. The system is documented on oracle bones from around the eleventh century BCE.
In the Tang dynasty (618–907) Chinese scholars — Li Xuzhong among them — began using the ganzhi calendar to read a person from the moment of birth. They formalized three pillars: year, month, day. This was the first version of the system, still without hour-level precision.
In the Song dynasty (960–1279) Xu Ziping added the fourth pillar: the hour. He shifted the analytical center from the year pillar to the day pillar. He also introduced the ten relationships (sipseong, 십성), which still organize interpretation today: how each element of the chart relates to the Day Master, whether it reinforces, cuts, or feeds. The method named after him — Japyeongbop (子平法, "Ziping method") — became the standard of the classical school.
Saju arrived in Korea along with other waves of cultural transmission from China, early in the Goryeo dynasty (918–1392). In the Joseon dynasty (1392–1910) it was taught alongside astronomy at the state observatory Gwansang-gam, which also prepared the calendar for the royal court.
The classical manual Ziping Zhenquan (子平真詮), still read by Korean practitioners today, postdates Xu Ziping by centuries. Compiled by Shen Xiaozhan during the Qing dynasty, it was published in 1779 — over seven centuries after the method itself. It contains the most complete exposition of gyeokguk (classical structures) and yongsin (balancing element) theory.
What saju is not
Saju is not a horoscope. It does not use the Western zodiac (Aries, Taurus, Gemini, the twelve sun signs). It is based on the Chinese solar calendar, which divides the year into twenty-four jeolgi (节气) — solar points marked by the sun's motion along the ecliptic. The month pillar comes from these points, not from the sun's position in the tropical zodiac.
Saju does not predict the future. The classical school does not say "you will meet a tall man in February." It says: "your day pillar carries wood yin; the decade of metal is approaching, and metal controls wood — this is a time of pressure and structuring." It reads patterns and predispositions. Not verdicts.
Saju is not a religion. It requires no faith. It works more like an archetype than a doctrine: a structural model that makes sense if you recognize your life in it. The classical schools treat saju as a tool of observation, not an object of worship.
Frequently asked questions
How does saju differ from Western astrology?
Saju reads a person through the element of the Day Master and the season of birth. Western astrology reads through the sun sign, the rising sign, and the positions of planets in twelve houses. Both systems try to describe the same person in different languages. Saju thinks in element proportions; Western astrology in planetary archetypes. They meet in the observation of pattern, diverge in the mechanics of description.
Do I need an exact birth time?
If you know it, use it. If you don't, saju still works. Three pillars (year, month, day) give a solid chart. The Day Master, sipseong, most of gyeokguk, and the dae-un cycles all function without the hour pillar. That is exactly how saju was read during the Tang dynasty, before Xu Ziping added the fourth pillar. The hour pillar adds the dimension of children, legacy, the second half of life, intimacy. When you know the exact time (to within about five minutes), the chart is fuller. When you don't, it is still yours.
Why do some calculators get it wrong for European users?
Because they ignore the difference between clock time and true solar time. For Wrocław in November the difference reaches twenty-four minutes — enough to fall into a different hour pillar. Full explanation: How ilju calculates your chart →
Will saju predict my future?
No. It shows tendencies. Dae-un (ten-year cycles) and se-un (annual cycles) answer the question "what kind of weather is approaching," not "what will specifically happen." Your choices remain yours. Saju gives you a map of the landscape you walk through.
Is saju religious?
No. It is a descriptive system, like Jung's archetypes or traditional Eastern medicine. It requires no faith; it works if it matches your experience.
How do I use the AI prompt?
Paste it into Claude, ChatGPT, or Gemini. You will get a first interpretation of your chart, in English or Polish. AI handles the basic aspects and configurations well; it will not replace the depth of a conversation with a human practitioner. For first orientation, it is enough.
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