I Ching divination

Among the many forms of divination is a cleromancy method using the I Ching (易經, yì jīng) or Book of Changes. I Ching consists of sixty-four hexagrams and commentary upon those symbols. Each hexagram is six lines, each one of which is either yin (represented by a broken line) or yang (a solid line). By randomly generating the six lines by one or other of various methods and then reading the commentary associated with the resulting hexagram, the sense(s) of that commentary is (are) then used as an oracle.

Certain schools of Chinese philosophy (such as the School of Yin-Yang, whose tenets were largely adopted by Daoism, though both are centuries younger than I Ching) maintain that powerful old yin will eventually turn to young yang and vice versa, so in addition to lines' being considered either yin or yang, they are also either young (i.e., stable) or old (i.e., changing); any hexagram that contains old yin or old yang lines (both being referred to as moving lines) thus also produces a second, different hexagram in which the moving lines of the first hexagram become their opposites (i.e., old yin becomes yang, and old yang becomes yin). The person consulting the oracle then also studies both the commentary specific to any moving line(s) and the commentary associated with the second hexagram formed when the indicated changes of lines have been made to the first.

Throughout China's region of cultural influence (including Korea, Japan and Vietnam), scholars have added comments and interpretation to this work, one of the most important in ancient Chinese culture; it has also attracted the interest of many thinkers in the West. Historical and philosophical information, as well as a list of English translations, can be found here. The text is extremely dense reading—it is not unknown for experienced soothsayers to ignore the text, interpreting the oracle from the pictures created by the lines, bigrams, trigrams, and final hexagram.

Several of the methods of consultation produce one number (6, 7, 8, or 9, corresponding to old yin, young yang, young yin, and old yang, respectively) per application of a more or less complex procedure, so that six passes through the procedure are required to generate one hexagram (or two hexagrams, if the first has any changing lines). Simpler (and sometimes less traditional) procedures can also be used.

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Wikipedia