The ruler of the hexagram (卦主): how to find the line that matters most

Most hexagrams have one line that gives the whole figure its character, and the tradition calls it the ruler of the hexagram (卦主, guazhu). The idea goes back to Wang Bi in the third century, and the Qing-dynasty Zhouyi Zhezhong (周易折中) refined it into two kinds of ruler: the line that constitutes the hexagram and the line that governs it. Knowing the ruler helps you see which line the Judgment is really about, and which moving line deserves the most weight in a cast.

Wang Bi: the few govern the many

In the section of his Outline of the Zhouyi (周易略例) that explains the Judgments, Wang Bi argues that a Judgment speaks of the hexagram as a whole and "makes clear the ruler from which it proceeds." His reasoning is almost political: 夫眾不能治眾，治眾者，至寡者也, "the many cannot govern the many; what governs the many is the very few."

That gives the first and simplest rule. If a hexagram has five lines of one kind and a single line of the other, the single line is the ruler. There are twelve such hexagrams:

• One yang among five yin: Fu (first line), Shi (second), Qian, Modesty (third), Yu (fourth), Bi (fifth), Bo (top).
• One yin among five yang: Gou (first), Tong Ren (second), Lü, Treading (third), Xiao Chu (fourth), Da You (fifth), Guai (top).

Look at Modesty and the rule becomes vivid: the lone yang line in the third place, "the noble one of modesty who works hard," is the modest person the hexagram is named for. In Fu, Return, the single yang line at the bottom is the return of light itself.

When no line stands out by number, Wang Bi says the meaning may instead come from the relation of the two trigrams, and no single line rules. Not every hexagram has a ruler in his sense, and he did not pretend otherwise.

The Tuan commentary points to rulers

Long before Wang Bi named the idea, the Tuan commentary was already explaining Judgments through a single line. Its phrases are the best clues you have:

• Da You, Great Possession: 柔得尊位大中，而上下應之, "the yielding gains the place of honour, great and central, and above and below respond to it." That is the yin fifth line.
• Bi, Holding Together: 以剛中也, "because it is firm and central." That is the yang fifth line.
• Shi, the Army: 剛中而應, "firm, central and responded to." That is the yang second line, the general, answered by the yin ruler in the fifth.

When the Tuan names a line with words like 剛中, 柔得中 or 得尊位, it is telling you which line rules.

Constituting and governing rulers

The Zhouyi Zhezhong, compiled in the early eighteenth century at the Kangxi emperor's command under Li Guangdi, set out a distinction that most later study follows. In its general principles it says there are two kinds of ruler:

• The constituting ruler (成卦之主) is the line that makes the hexagram what it is, whatever its position and whether its character is good or bad. A line that brings danger can be a constituting ruler, because the danger is what the hexagram is about.
• The governing ruler (主卦之主) is a line of good character that holds the right time and the right place. It is most often the fifth line, though other lines are sometimes chosen.

Sometimes the same line is both; sometimes they differ. Lü, Treading, shows the difference within the Tuan itself. It begins 柔履剛也, "the yielding treads upon the firm": the lone yin third line, treading on the tiger's tail, is what constitutes the hexagram. But it goes on to praise the fifth line, 剛中正，履帝位而不疚, "firm, central and upright, it treads the place of the sovereign without fault": that is the line that governs. The hexagram is about treading on danger; the right way to tread is shown by the fifth.

The Zhezhong also allows a hexagram to have more than one ruler of either kind. Treat the two categories as questions you can ask, not as a key that settles every case.

How to find the ruler

When you want to know a hexagram's ruler, work through these steps in order:

• Count the lines. If one line is alone in its kind, start there; it is almost always at least the constituting ruler.
• Read the Tuan. Look for a line it singles out: firm and central, yielding and central, gaining the honoured place, responded to above and below.
• Check the fifth line. If it is central and its text is favourable, it is the likely governing ruler, especially if the Tuan praises the centre.
• Read the name. Ask which line embodies the hexagram's name. In Modesty it is the modest line; in Guai, Breakthrough, the top yin line is the one being broken through.
• Accept when there is no clear ruler. Some hexagrams are better read through their two trigrams than through any one line.

For the position principles behind these choices, see correct place and central lines; for the relations that link the ruler to the other lines, see correspondence and holding together.

Why the ruler matters in a reading

The rules for changing lines that most readers follow come from Zhu Xi, and they do not mention rulers at all. The ruler is an interpretive tool, not a casting rule. But it changes how you weigh what you see:

• If the ruler is your moving line, the change touches the heart of the situation. Read its text as the main message and the Judgment as its frame.
• If a different line moves, read it in relation to the ruler. Is it close to the ruler, corresponding with it, riding over it? Its role in the situation is defined partly by how it stands to the centre of power.
• If several lines move, the ruler among them can help you decide which to stress when the line texts seem to pull in different directions.
• If no lines move, the ruler still tells you what the Judgment is pointing at, which is often the clearest way into a static hexagram.

The next time you cast a reading, look first for the ruler before you read the lines. Knowing who holds the centre of the situation makes it much easier to see where you stand in it.