“When the Yin and the Yang keep precisely to their proper positions, then there is quiet and peace. But if (the balance) leans to one side, then there is wind, if they clash there is thunder, if they cross each other’s path there is lightning, if they are in confusion, there is fog and clouds, if they are at harmony there is rain. 

If the Yang force conquers, clouds and rain result; if the Yin force conquers, ice and frost are formed. Absolute supremacy of the Yang leads to hail, the converse leads to sleet. These are the changes of the two fundamental forces. 

Hairy animals acquire their coats before coming into the world, feathered ones similarly first acquire their feathers. Both are born by the power of Yang. Animals with carapaces and scales on their bodies likewise come into the world with them; they are born by the power of Yin. Man alone comes naked into the world; (this is because) he has the (balanced) essences of both Yang and Yin.

The essence (or most representative example) of hairy animals is the unicorn, that of feathered ones is the phoenix (or pheasant); that of the carapace-animals is the tortoise, and that of the scaly ones is the dragon. That of the naked ones is the Sage. The dragon cannot rise up without wind; the tortoise cannot foretell the future without (the application of) fire. These are examples of the action of Yang on the Yin. These four (numinous) animals are the aids of the spirit of the Sage. Thereby the sage can be the master of heaven and earth, the master of the mountains and the rivers, the master of the gods and the spirits, and the master of the sacrifices in the ancestral temple. 

The sage marks carefully the Numbers of the sun and moon, so that he can observe the motions of the stars and the constellations, and thence arrange the four seasons in order according to their progressions and retrogradations. This is called the ‘calendar’ (li). The sages invented the twelve musical tubes, so as to provide standards for the eight notes, high and low, clear or blurred. These are called the ‘pitchpipes’ (lü). The pitchpipes are in the domain of the Yin but they govern Yang proceedings. The calendar comes from the domain of the Yang, but it governs Yin proceedings. The pitchpipes and the calendar give each other a mutual order, so closely that one could not insert a hair between them.” (Ta Tai Li Chi)

12 tubes + 8 notes = 20 items of music.12 months + 8 moon periods = 20 items of calendar.