Two Yi: Two factors or things with the properties of yin and yang opposition and coexistence.
For example, heaven and earth, men and women, day and night, odd and even, hardness and softness, heaven and earth, in short, all things in the universe that can be divided into two.
Two Yi can generally be understood as yin and yang.
Examples of natural and social yin and yang:
The sky is yang, and the earth is yin.
The sun is yang, and the moon is yin.
Day is yang, night is yin.
Bright is yang, dark is yin
Above is yang, below is yin.
Movement is yang, stillness is yin.
Men are yang, women are yin.
A gentleman is yang, while a petty person is yin
Between heaven and earth, when you observe anything, there is nothing that does not have the phenomenon of yin and yang. Every movement and stillness of all things, and every movement and breath of human beings contain the profound principles of yin and yang.
Tai Chi Sheng Two Yi
The drawings of the Yang and Yin lines in the Book of Changes are presented above