Setting up the four pillars: solar months, the year boundary and the midnight hour

The four pillars of a Four Pillars of Destiny (BaZi) chart come from the year, month, day and hour of birth, and three points in setting them up need the most care. The month follows the solar terms, not the lunar calendar; the year changes at the Start of Spring, around February 4; and the day changes at midnight, which splits the Rat hour, 23:00 to 00:59, between two days.

Each pillar is one heavenly stem over one earthly branch. Setting them up can look like simply looking things up in a table, but these three points are where checking matters most. This lesson goes through them one by one, to help you check your own four pillars.

The month pillar: set by the solar terms

The months of BaZi are not lunar months but solar months, set by the solar terms. The year has twenty-four solar terms, and twelve of them each begin a month: the Start of Spring begins the Tiger month, Awakening of Insects begins the Rabbit month, and so on. The original notes to Dripping Heavenly Marrow (滴天髓), describing which hidden stem is in command in the Tiger month, count the days from the Start of Spring; Commentary on the True Interpretation of Ziping (子平真诠评注; ROC, 1936), listing month by month how many days each hidden stem is in command, also counts each month from the solar term that begins it.

Dripping Heavenly Marrow · The Month Branch, original notes; Commentary on the True Interpretation of Ziping · On the Rise and Fall of Yin and Yang

The date and moment of each solar term vary a little from year to year, so check a perpetual calendar for your birth year. If you were born on the day a solar term begins, look at whether your time of birth falls before or after the moment it begins: before it, you still belong to the previous month; after it, you are in the new month.

The month branch is fixed, but the month stem changes with the year stem. Explaining why stems act while branches hold, Commentary on the True Interpretation of Ziping gives an example: in a Yang Wood or Yin Earth year the first month is Yang Fire Tiger, and in a Yin Wood or Yang Metal year it is Yang Earth Tiger; the first month is always the Tiger, and the second always the Rabbit.

Commentary on the True Interpretation of Ziping · On the Ten Stems and Twelve Branches

The five full pairings are below. After the Tiger month the stems run on in order: in a Yang Wood year, for example, the Tiger month is Yang Fire Tiger, so the Rabbit month is Yin Fire Rabbit and the Dragon month is Yang Earth Dragon.

The year pillar: set by the Start of Spring

Following the common practice, this series takes the Start of Spring as the beginning of the year: if you were born before the Start of Spring, your year pillar still belongs to the previous year, and only after it does the new year begin. This keeps the year and the month in step, since the Start of Spring begins both the Tiger month and the new year. So if you were born in January or early February, check carefully: the calendar year has already changed, but your year pillar may not have.

Some calendars and methods change the year at Lunar New Year, and some change the day at 23:00; this series follows the Start of Spring for the year and midnight for the day.

The day pillar: sixty pairs, day after day

The day pillar runs through the cycle of sixty stem-and-branch pairs, one day after another without a break, unaffected by long or short months or by leap months. To find it, look it up in a perpetual calendar. This series takes midnight as the boundary between days; a birth in the Rat hour, around midnight, is covered separately below.

The hour pillar: twelve two-hour periods

The day is divided into twelve periods of two hours each, one for each branch:

The hour stem changes with the day stem. The table below gives the Rat-hour pillar for each day stem; the later hours run on in order, so on a Yang Wood day the Rat hour is Yang Wood Rat and the Ox hour is Yin Wood Ox.

The hour pillar is more than two extra characters. Right after the month branch, Dripping Heavenly Marrow turns to the hour of birth:

生时乃归宿之地，譬之墓也，人元为用事之神，墓之定方也，不可以不辨。

Our translation: The hour of birth is the place where the chart comes to rest, likened to a resting place; its hidden stem in command is the direction the resting place faces, and it must be told apart.

If the month branch is like a house, the hour of birth is like the place where the whole chart finally comes to rest; the hour, too, has a hidden stem in command at the time, and it must be told apart as well. The original notes take the Rat hour as an example: in its short first part, about three tenths of the hour, Yang Water is in command; in its longer later part, about seven tenths, Yin Water is in command. So people born on the same day but at different hours, or even early or late in the same hour, differ in the finer details of their charts.

Dripping Heavenly Marrow · The Hour of Birth, original notes

The Rat hour across midnight: early and late

The Rat hour runs from 23:00 to 00:59, straight across midnight. If you were born in these two hours, first settle which day your day pillar belongs to.

This series’ method is that the day changes at midnight, so the Rat hour is split into two parts.

• Early Rat hour, 00:00–00:59, belongs to the new day: the day pillar is the new day’s, and the hour pillar is that day’s Rat hour.
• Late Rat hour, 23:00–23:59, still belongs to the previous day: the day pillar does not change, but the hour pillar is taken from the next day’s Rat hour.

For example, say one day is a Yang Wood day and the next is a Yin Wood day. Born at 23:30, the day pillar is still the Yang Wood day’s pillar, and the hour pillar is taken from the Yin Wood day’s Rat hour: Yang Fire Rat. Born at 00:30 the next morning, the day pillar is the Yin Wood day’s, and the hour pillar is again Yang Fire Rat.

The name "late Rat hour" (夜子时) appears in Dripping Heavenly Marrow Elucidated (滴天髓阐微; Qing dynasty, 19th century), in its discussion of the hour of birth. Explaining the short first part of the Rat hour that the original notes give to Yang Water, it says that part is residual energy carried over from the Pig, and calls it the late Rat hour. The book uses the name to explain the order in which hidden stems take command within an hour; taking midnight as the boundary for the day pillar is the method this series follows. Comprehensive Guide to the Three Fates (三命通会; Ming dynasty, 16th century) gives the division of the hours a chapter of its own, On Hours and Their Subdivisions.

Dripping Heavenly Marrow Elucidated · The Hour of Birth

Try it on your chart

1. Year pillar. If you were born between January 1 and about February 5, look up the date and moment of the Start of Spring in your birth year, and see whether you were born before or after it.
2. Month pillar. Find the last solar term that begins a month before your birth to fix the month branch, then work out the month stem from the year stem. If you were born on the day a solar term begins, compare your time of birth with the moment it begins.
3. Day pillar. If you were born at 23:00–23:59, the day pillar is that same day’s; if you were born at 00:00–00:59, it is the new day’s.
4. Hour pillar. Find the hour branch, then work out the hour stem from the day stem; for the late Rat hour, use the next day’s day stem.
5. Once everything is checked, write down your eight characters. Every lesson that follows starts from them.

See also: The ten heavenly stems and twelve earthly branches

See also: Hidden stems: what each branch holds