To the ancient Chinese, Yin ( represented by the broken line ) had connotations of; "shady, secret, dark, mysterious, cold.
Yang, the opposite of Yin, ( and represented by the unbroken line ) links to ideas of "clear, bright, the sun, heat".
From these basic opposites, a complete system of opposites was developed.
Yin represents everything about the world that is dark, hidden, passive, receptive, yielding, cool, soft, and feminine.
Yang represents everything about the world that is illuminated, evident, active, aggressive, controlling, hot, hard, and masculine.
Everything in the world can be identified with either Yin or Yang. Earth is the ultimate Yin object. Heaven is the ultimate Yang object.

Although it is correct to see Yin as feminine and Yang as masculine, everything in the world is really a mixture of the two, which can mean that female beings might actually be mostly Yang and male beings might actually be mostly Yin.
The familiar diagram ( at the top of this page), shows Yin and Yang flowing into each other, they do not merely replace each other but actually become each other.

When it comes to the "five elements", earth, water, and wood are clearly to be associated with Yin. Water, the softest and most yielding element, becomes the supreme symbol of Yin and Fire (the hottest element) and metal (the hardest) both are associated with Yang.


The ancient Chinese thought of South as being the top of their compass, so the diagram at the top of the page has pure "Yin" ( 3 broken lines ) in the South-West, and pure "Yang" ( 3 unbroken lines ) in the North-West.
The I Ching is based on the principle of a broken line, representing Yin, and an unbroken line, representing Yang. ( These surround the Yin and Yang symbol at the top of this page). The I Ching groups the lines into sets of threes (the trigrams) and into sets of sixes (the hexagrams).
There are eight trigrams: The arrangement of the trigrams around the compass reflects Chinese geomancy (Feng Shui), i.e. the determination of the auspicious or inauspicious situation and orientation of places (cities, temples, houses, or graves). Chinese cities are properly laid out as squares, with gates in the middle of the sides facing due north, east, south, and west. The diagonal directions are then regarded as special "spirit" gates: Northwest is the Heaven Gate; Southwest the Earth Gate; Southeast the Man Gate; and Northeast the Demon Gate. The Northeast was thus the direction from which malevolent supernatural influences might particularly be expected.
This illustrates an important aspect of the theory of Yin and Yang: Because the "Way of the Tao is Return," Yin and Yang, when they reach their extremes, actually become their opposites. The "old" lines therefore change into their opposites, giving us two hexagrams if any changing lines are involved: the first hexagram, representing the current state of affairs; and the second hexagram, after the changes have been made, representing the future state of affairs.