The Book of Changes or the I Ching is among the oldest writings preserved to the present day. Its origins are in ancient China and it has become increasingly well known in the West since the late 19th century. The I Ching's principal use is in divination.
To consult the I Ching, one formulates a question and casts the I Ching using coins or yarrow sticks. Both methods are seemingly random, bypassing the conscious mind and allowing 'spirit to guide the draw. The process produces a hexagram, consisting of 6 lines. A line is represents either a yin or a yang and can be changing or stable. Thus, each casting the I Ching can produce 4 to the 6th power, that is 4096 different results. The result consists of one hexagram, a collection of six lines, one of 64, two (to the sixth power) different hexagrams. A second hexagram is constructed by reversing each of the changing lines of the first, so that a changing yin becomes a yang and vice versa. A hexagram may have from zero to six changing lines but on the average, at least using the coins method, 1-5 lines will be changing. The book contains an interpretation text for each of the hexagrams, with a special passage for each of the changing lines. The text of the first hexagram, the text of the changing lines following the text of the first hexagram plus the text of the resulting hexagram together compose the reading.
The hexagrams themselves have complex symbolic structure and form families and sequences. A single hexagram may be seen to represent a situation. Each line represents a component of the situation. Changing the line leads to a resulting hexagram through a process of transition represented by the text of the line. The I Ching may be used as a method of analysis without any random process by simply looking for a hexagram embodying the situation to be analyzed and looking at the possible changes. The philosophical tone of the I Ching is inherently cyclic, with all processes being reversible and constantly in flux, with increase, decrease, stability and turmoil alternating. The symbols are very generic and lend themselves to representing interpersonal situations, situations of society or organization as well as the inner life of man.
When used as an oracle, we can think of the I Ching as a dictionary used for receiving messages. As such it is not fundamentally different from using cards or some other method. The versatility of its symbols and its specific structure do give it a characteristic flavor and richness of tone, however.
If we consider the I Ching as a means of receiving communications from the spiritual world, communications which are limited in their data rate by various factors, we can hardly conceive of an encoding that would deliver more semantic payload for only 12 bits of data than the I Ching. Of course, consistently with the Law of Confusion, the reality of any such communication is undemonstrable in materialistic terms.