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Foundation of the trigrams:

The trigrams are born as the combination of Yin and Yang energy in 3 times or impulses.

In addition to the stable and pure Yin and Yang energies (Heaven, the creative and Earth, the receptive), there are six other trigrams, covering all possible combinations between the lines.

The simplest way to understand them is family ordering. Between the trigrams, Chien, the sky, corresponds to the father and Kun, the earth, corresponds to the mother. Then there are three sons who represent the evolution of the Yang energy (Chen, Kan and Kun), and three daughters who do the equivalent with the Yin disposition (Sun, Li, Tui).