The hexagrams should be thought of not merely as made up of six individual lines but always as composed of two primary trigrams.
In the interpretation of the hexagrams, these primary trigrams play a part according to the various aspects of their character-first according to their attributes, then according to their images, and finally according to their positions within the family sequence.
These general meanings, particularly when it is a question of interpretation of the individual lines, must be supplemented by the lists of symbols and attributes -at first glance seemingly superfluous-given in Discussion of the Trigrams. (See "Definition")
In addition, the positions of the trigrams in relation to each other must be taken into account.
From these characterizations of the trigrams-already in use in the Commentary on the Decision-there was later constructed a system of transforming the hexagrams one into another, which has led to much confusion.
This system is here left wholly out of account, since it is not in any way essential to the explanation. Nor has any use been made of the "hidden" hexagrams - i.e., the idea that basically each hexagram has its opposite hidden within it (for example, within Ch'ien is K'un, within Chên is Sun, etc.).
But it is decidedly necessary to make use of the so-called nuclear trigrams, hu kua. These form the four middle lines of each hexagram, and overlap each other so that the middle line of the one falls within the other.
An example or two will make this clear:
The hexagram Li, THE CLINGING, FIRE (30)
|shows a nuclear trigram complex consisting of the four lines|
The two nuclear trigrams are :
|Tui, the Joyous, as the upper|
|Sun, the Gentle, as the lower|
These relationships correspond exactly with the evaluations of the lines in the appended judgments.