What Is Saju? — A Beginner's Guide

Saju (四柱), also known internationally as BaZi or the Four Pillars of Destiny, is an East Asian system developed over roughly a thousand years for ‘reading a person through time.’ It originated in China and spread to Korea, Japan, Vietnam, and elsewhere — each country developed it slightly differently, but the core structure is the same. (Throughout these guides we use the Korean name ‘Saju,’ but the system is the same as BaZi.)

The name captures the system in a single phrase. ‘Saju (四柱)’ literally means ‘four pillars.’ A person's life is seen as supported by four pillars.

Let's start by looking at what those four pillars are.

The four pillars are the four time markers of birth: (1) year, (2) month, (3) day, (4) hour. Each pillar carries two characters, so a person's Saju has four pillars × two characters = eight characters in total.

These eight characters are what East Asia has long called ‘Palja (八字, the eight characters).’ For centuries this combination has been seen as the blueprint a person is born with.

In each pillar, the upper character is called the ‘heavenly stem (天干)’ and the lower character is called the ‘earthly branch (地支).’ There are 10 heavenly stems and 12 earthly branches. Characters like ‘Gap, Eul, Byeong, Jeong…’ are stems, and ‘Ja, Chuk, In, Myo…’ — the characters used for the East Asian zodiac animals — are branches.

Once the eight characters are set, that's not the end. Each character is then mapped to one of the ‘five energies (Wuxing).’

Here's a common misconception: Wuxing is not about ‘physical substances’ but about ‘five directions of movement.’ It's traditionally translated as ‘Wood, Fire, Earth, Metal, Water,’ which makes it sound like a list of objects, but it actually represents five flows of energy observed in nature. The character ‘行’ in ‘五行 (Wuxing)’ literally means ‘movement.’

The five flows can be summarized this way.

Wood (木) is the energy of upward extension. Like a sprout breaking through frozen ground, it's the movement of beginning and growing.

Fire (火) is the energy of outward expansion. The upward flow reaches its limit and bursts outward in all directions — the movement of a midsummer heatwave or a roaring flame.

Earth (土) is the position of pause and transition. The endlessly expanding flow is brought to a halt and handed over to the next stage — like the brief pause at the apex before a thrown ball begins to fall.

Metal (金) is the energy of inward contraction. The flow that was spreading outward turns inward and condenses into something solid — the descending quality of fruit ripening and leaves falling in autumn.

Water (水) is the state of deep condensation and storage. Contraction has reached its extreme, and energy is gathered in the lowest, deepest place — the latent energy that prepares for the next ‘Wood (beginning).’

When you map a person's eight characters into the five flows, you get a picture like ‘this person has strong Fire energy (expansion) and weak Water energy (condensation).’ Don't read it as ‘too much fire’ — read it as ‘a person whose movement strongly tends toward outward expression.’

This balance shapes a person's temperament, the kinds of work and environments that suit them, and patterns in relationships. A weak flow doesn't mean a ‘defect’ — it means ‘this person tends to do better when they meet environments, people, or periods that supplement that flow.’

Saju tries to answer roughly four questions.

First, ‘what kind of nature was this person born with?’ This refers to the innate temperament, strengths, and weaknesses, as read through the balance of the five energies.

Second, ‘who matches well with this person?’ Two people's Saju are placed side by side, and whether the five energies complement or clash is examined. This is what's commonly called ‘compatibility (gunghap).’

Third, ‘how do the larger currents of life flow?’ The clock called ‘Dae-un (大運)’ reads the broad mood that shifts every 10 years.

Fourth, ‘what's the flow of the current period?’ The energy of the current year and month (se-un, wol-un) is matched against the natal Saju.

If you read the same person through Western astrology or Vedic astrology, you also get results. The three simply look from different angles.

Western astrology reads a person through ‘planets and zodiac positions.’ Rather than translating into characters and energies as Saju does, it reads life through the web of planetary positions itself.

Vedic astrology (the Indian tradition) is similar to the Western system in that it uses planets, but it places more weight on ‘the actual positions of stars’ and on the ‘Dasha (timing system).’

The three systems do not translate into one another. Think of them as three photographs of the same life from different angles. Where they meet and where they diverge is covered in more detail in the other guide articles.