Wu Chi

The origin of the I Ching begins with the "Wu Chi", which means "What there is before the universe comes into being."

Tao

"Wu Chi" can be thought of as negative space with the potential for change, which brings the universe or "Tao" into being.

Yin & Yang

The Tao (also known as the Grand Terminus) in turn generates the two forms of Yin & Yang.

The Four Symbols 

The Trigrams (Pa Kua)

When we introduce the next set of lines to the four symbols we get the eight sets of three lines known as the Trigrams or "Pa Kua".