The I Ching (often spelled as I Jing, Yi Ching, Yi King, or Yi Jing; also called "Book of Changes" or "Classic of Changes") is the oldest of the Chinese classic texts. A symbol system designed to identify order in what seem like chance events, it describes an ancient system of cosmology and philosophy that is at the heart of Chinese cultural beliefs. The philosophy centers on the ideas of the dynamic balance of opposites, the evolution of events as a process, and acceptance of the inevitability of change (see Philosophy, below). In Western cultures, the I Ching is regarded by some as simply a system of divination; many believe it expresses the wisdom and philosophy of ancient China.
The text of the I Ching is a set of predictions represented by a set of 64 abstract line arrangements called hexagrams (卦 guà). Each hexagram is a figure composed of six stacked horizontal lines (爻 yáo), where each line is either Yang (an unbroken, or solid line), or Yin (broken, an open line with a gap in the center). With six such lines stacked from bottom to top there are 26 or 64 possible combinations, and thus 64 hexagrams represented.
The hexagram diagram is conceptually subdivided into two three-line arrangements called trigrams (卦 guà). There are 23, hence 8, possible trigrams. The traditional view was that the hexagrams were a later development and resulted from combining the two trigrams. However, in the earliest relevant archaeological evidence, groups of numerical symbols on many Western Zhou bronzes and a very few Shang oracle bones, such groups already usually appear in sets of six. A few have been found in sets of three numbers, but these are somewhat later. Note also that these numerical sets greatly predate the groups of broken and unbroken lines, leading modern scholars to doubt the mythical early attributions of the hexagram system (see, e.g., Shaugnessy 1993).
Each hexagram represents a description of a state or process. When a hexagram is cast using one of the traditional processes of divination with I Ching, each of the yin or yang lines will be indicated as either moving (that is, changing), or fixed (that is, unchanging). Moving (also sometimes called "old", or "unstable") lines will change to their opposites, that is "young" lines of the other type -- old yang becoming young yin, and old yin becoming young yang.
The oldest method for casting the hexagrams, using yarrow stalks, is a biased random number generator, so the possible answers are not equiprobable. While the probability of getting either yin or yang is equal, the probability of getting old yang is three times greater than old yin. The yarrow stalk method was gradually replaced during the Han Dynasty by the three coins method. Using this method, the imbalance in generating old yin and old yang was eliminated. However, there is no theoretical basis for indicating what should be the optimal probability basis of the old lines versus the young lines. Of course, the whole idea behind this system of divination is that the oracle will select the appropriate answer anyway, regardless of the probabilities. (Wikipedia)
