It operates in a twofold way, by expansion and contraction, or by ceaseless active and passive pulsations.

The active expansive pulsation is called Yang, the passive intensive pulsation is Yin, and the two may be called the Positive and Negative Essences of all things.

When the active expansive phase of the process has reached its extreme limit, the operation becomes passive and intensive; and from these vibrations originate all material and mortal existences.

Creation is therefore a perpetual process,--matter and spirit are opposite results of the same force.

The one tends to variety, the other to unity; and variety in unity is a permanent and universal law of being.