"The concept of yin and yang originates in ancient Chinese philosophy and metaphysics, which describes two primal opposing but complementary forces found in all things in the universe. Yin, the darker element, is passive, dark, feminine, downward-seeking, and corresponds to the night; yang, the brighter element, is active, light, masculine, upward-seeking and corresponds to the day.
The pair probably goes back to ancient agrarian religion; it exists in Confuciasm, and it is prominent in Taoism. Though the words yin and yang only appear once in the "Tao Te Ching", the book is laden with examples and clarifications of the concept of mutual arising.
Yin and yang are descriptions of complementary opposites rather than absolutes. Any yin/yang dichotomy can be seen as its opposite when viewed from another perspective. The categorization is seen as one of convenience. Most forces in nature can be broken down into their respective yin and yang states, and the two are usually in movement rather than held in absolute stasis."
"This Symbol is used in Logos, on book covers, in the New Age Movement, in martial arts and so forth. Yin and Yang are considered to be opposites. Yin represents eternity, dark ,feminine, left side of the body etc. Yang is its opposite and represents history, light, masculine, right side of the body etc. Yang is male, positive and represented by the sun. Yin is female, negative, and represented by the moon, says Paul E. Desautels in the Gem Kingdom.
The Symbol itself dates back at least to the fourth century BC. and has been identified with the Eastern philosophical religions of Confucianism, Buddhism, and Taoism. In the Western World it has long been adopted into the symbolism of myth, magic, astrology and witchcraft.
A book, Black Magic, White Magic, explains the Yin-Yang like this: Another ancient magical sign called the yin-and-yang first appeared sometime before the 3rd century BC. in China. This emblem became a favourite of Sorcerers and mystics throughout the Orient because it, too, embodies so many possible meanings.
One well-known witch who is called the "mistress of the occult", proclaims that the Yin-Yang theory is: ...an idea that inspired such things as Chinese boxing, breath control [used in yoga, meditation etc.], the use of special herbs, and some rather erotic sexual exercises designed to nourish the Yang with the Yin.
The concept of Yin and Yang (also called Tai-gi-tu), likewise plays an important role in many other occult practises. For instance, the Dictionary of Mysticism states the following about the practise of shu shu: The Ancient Chinese system of Magic, divination, and occult practises including astrology, dream interpretation the art of co-ordinating human affairs by the active and passive principles of the universe (yin yang) and Five Elements (wu shing), fortune telling by the use of the stalks of the divination plant and the tortoise shell, and miscellaneous methods such as dream interpretation, the regulation of forms and shapes of buildings, etc."
"The two contrary cosmological basic principles of Chinese philosophy to which all things, being, events and time periods are ordered. Corresponding to the Yin principle are the negative, the feminine, darkness, the earth, passivity, wetness, and the broken line, corresponding to the Yang principle are the positive, the masculine, brightness, the sky, activity, dryness, and the unbroken line. The two principles represent the polarisation into which the unity of the primeval beginning separated. They are visually represented as a circle that is divided symmetrically by a serpentine line; of the two areas thereby produced, one is dark, the other light; in the middle of each area, however there is a spot that is the colour of the other area, which a sign of the mutual dependency of both principles; the powers of Yin and Yang are never fundamentally opposed to one another and alternatingly wax or wane periodically in definite periods of time."