Yin and Yang Lines in the I Ching: Old and Young Lines, and What 6, 7, 8 and 9 Mean
The four numbers
| Number | Name | Yin or yang | Changes? |
|---|---|---|---|
| 6 | Old yin | Yin | Changes to yang |
| 7 | Young yang | Yang | Does not change |
| 8 | Young yin | Yin | Does not change |
| 9 | Old yang | Yang | Changes to yin |
Odd numbers are yang and even numbers are yin. 7 and 9 are yang; 6 and 8 are yin.
These four numbers come from the yarrow-stalk method: after three changes, the remaining stalks are counted off in fours, giving nine, eight, seven or six groups of four (see the yarrow-stalk method). The coin method adds up backs at 3 and inscribed sides at 2, and arrives at the same four numbers.
Why the old change and the young do not
Yang grows from 7 to 9, and 9 is yang at its extreme. Yin shrinks from 8 to 6, and 6 is yin at its extreme. Whatever reaches its extreme turns back: yang at its limit turns to yin, and yin at its limit turns to yang. 7 and 8 are still midway, so they do not change.
This is also the root of what the Zhouyi means by "change": the divination looks for where the movement is, which is why the changing lines are the lines to read.
Why lines are labeled nine and six
In "Nine at the beginning" (初九), "Six in the second place" (六二), "Nine in the fifth place" (九五) and "Six at the top" (上六), the nine and the six only tell you whether the line is yang or yin. They do not say the line is necessarily changing. The Zhouyi divines by change, so it uses the numbers that change, nine and six, as its names for yang lines and yin lines.
The places, from the bottom up, are called beginning (初), second, third, fourth, fifth and top (上). In Chinese the bottom line is written place first, "beginning nine" (初九), not "nine beginning", and the top line likewise, "top nine" (上九); the four middle lines are written number first, as in "nine second" (九二) and "six third" (六三).
All nines, all sixes
Of the sixty-four hexagrams, only Qian (Heaven) and Kun (Earth) have one extra text. Qian has All nines (用九): "A host of dragons appears, and none pushes to the head. Good fortune." and Kun has All sixes (用六): "It is favorable to stay true forever.". When all six lines are old yang or all six are old yin, so that all six lines change, this is the text you read.