Xu refers to a state of the cosmos or a state of mind. Basically, it has two different meanings. The first refers to the origin of the universe, indicating that everything originates from xu. Different ancient thinkers have different interpretations of this notion: Some take xu as being devoid of anything; others believe it is the state of existence of qi (气). Because qi is invisible and formless, it is said to be empty, but not a vacuum totally devoid of anything. The second meaning of xu refers to a state of mind that is peaceful, not preoccupied or simply free of any preconceptions.
Void and peace mean that all distractions, such as desires and rational thoughts, should be dispelled to attain peace and purity of the soul. The idea of void and peace was first proposed by Laozi and Zhuangzi(369?-286 BC), the founders of Daoism, and then used by Xunzi (313?-238 BC) to refer to a state of mental concentration. Such a state of mind is similar to the psychological conditions in appreciation of works of literature and art, which are characterized by being totally free from the awareness of oneself and the outside world, and free from any urge and desire. Therefore, thinkers and literary critics of earlier times used this term to explain the state of mind in literary and artistic creation and appreciation. It stressed the need for spiritual freedom in artistic creation, suggesting that this is an important precondition for reaching the highest level of aesthetic appreciation.
Qi (vital force) has a material existence independent of subjective consciousness and is the basic element of all physical beings. It is also the basis for the birth and existence of life and spirit. In addition, some thinkers have given a moral attribute to qi. Qi is in constant motion and change, and has no specific shape. Its concentration gives birth to a thing and its evaporation signals the end of that thing. Qi permeates all physical beings and their surroundings. Qi, as a philosophical concept, is different from what is commonly understood by the word qi (气), namely, air. Although things in liquid or solid form are different from things in air form, from the perspective of the ancient Chinese philosophy, their formation and existence are the results of the concentration of qi.
The term refers to a state of mind that is completely empty and void. It originates from the book Zhuangzi, in which the meaning of the term was explained by Confucius (551-479 BC) to Yan Hui (521-481 BC). Zhuangzi (369?-286 BC) believed that one’s ears and heart distinguish between oneself and others and between right and wrong, while qi (气 vital force), shapeless and empty, exists in everything and does not come into conflict with anything. Therefore, one’s mind should be empty like qi when coming into contact with external things so that one will not be different or clash with them. When one’s mind roams beyond physical things, freeing itself from the constraints and influence of other things, it maintains a state known as the “pure state of mind.”
This refers to a state of mind Xunzi (313?-238 BC)proposed as a way to master the dao of general morality. He believed that one gets to know dao through the action of one’s heart and mind. But since the human heart and mind are often closed, they can only function normally when one is open-minded, concentrated, and consequently tranquil. Xu (虚), or open-mindedness, prevents prior knowledge from hindering the acquisition of new knowledge. Yi (壹), or concentration, allows one to assimilate knowledge of different categories while keeping them from interfering with each other. Jing (静), or tranquillity, is to keep the false and confusing knowledge from obstructing one’s normal process of contemplation.