Generally speaking, Yin and Yang are complementary opposites and are the two factors which combine to form Tai Chi. Since Tai Chi itself is an abstract concept, the Universe and all the matter in it cannot be understood until after Tai Chi is divided into, and analysed in accordance with, Yin and Yang. Yin signifies softness, weakness, female, stillness, interior, bending, Earth, Moon, night, negative, and the dark side of all matter. Yang signifies hardness, strength, male, motion, exterior, unbending, Heaven, Sun, day, positive and the bright side of all matter.
In a favourable environment Yin and Yang will interact and develop, but in an unfavourable environment they will repel one another and destroy all matter. Yin and Yang counteract and yet interact. When in any one situation their interaction reaches a conclusion, the natural phenomena in that situation will follow a pattern of variation in constant repetition, as is shown in the diagrams set out below. These diagrams, in representing the changes of Yin and Yang, also represent the Four Emblems:-
A. Young Yang
Yang is ascending while Yin is descending. Yang here represents spring, brightness and the sun. In terms of time, it is the morning of the day. This is why this propitious motif is shown on the cover of this book and also should be the motif of all Tai Chi Chuan schools.
B. Old Yang
Yang is on top while Yin is underneath. This is Yang at its strongest point, where it completely dominates Yin. This means the sun is at its zenith and the time is noon. It is now summer time.
C. Young Yin
Yang is now descending while Yin is ascending. Yin represents the moon and darkness, so it is now evening time. The brightness of the sun is now on the wane. The leaves are falling and autumn has come.
D. Old Yin
Yang has reached its nadir while Yin has reached its zenith. Yin has followed Yang as night follows day. The time is now midnight. Old Yin will be followed by Young Yang. Winter in now with us.