What are two musical instruments?

The word "two vessels" in classical Chinese means "two representations of the universe", which represents the vague and abstract understanding of the stars in the universe of ancient China. Originated from the ancient people's view of nature in China. The ancients observed various opposing and related natural phenomena in nature, such as heaven and earth, sun and moon, day and night, cold and heat, men and women, up and down, etc.

In the way of philosophical thinking, the concept of "Yin and Yang" is summarized, and Yin and Yang also map the understanding of opposition and related relations in this kind of nature, so it is generally recognized that "Er Yi" mainly refers to "Yin and Yang".

As early as the Spring and Autumn Period, Yin and Yang were mentioned in Yi Zhuan and Lao Zi's Tao Te Ching. The theory of Yin and Yang has penetrated into all aspects of China's traditional culture, including religion, philosophy, calendar, Chinese medicine, calligraphy, architecture, geomantic omen, divination and so on. Yin and Yang are the division or subdivision of "unity of opposites or contradictory relationship". These philosophical thoughts and ideas still have a wide influence today.