There are 8 fundamental trigrams in I-Ching which derived from 3 parallel lines. These lines are made of different combinations of Yin and Yang. Their combination of every possibility resulted in 64 hexagrams. These hexagrams are often separated into three different formats. Circular format indicates time and heaven.
Square format denotes space and earth.
The third combines them by having circular arrangement enclosing square design. It symbolizes the added dimension of man, and his interaction with time and space. Together, both 8 trigrams and their expansion of 64 hexagrams, encompassed all of changing cosmic and physical conditions found on earth. In I-Ching, Tai Chi represents great cosmos. The cosmos is there, and perhaps has always been there.