The Chinese character Romanised as "I" represents easiness, clarity, change and changelessness. "Ching" may be transliterated as "a classic" (book/writing). "I Ching" therefore translates as "The Classic book of Change". Interpretation suggests ways in which nature society and the individual could or should work together.
The I Ching is most known or recognised by westerners as a method of divination and often perceived as some kind of fortune telling based upon instinct or extraordinary almost supernatural ability - like reading tea leafs in the bottom of a cup or lines on a person's palm. This erroneous interpretation by many westerners is perhaps excelled only by our attempts to Feng Shui our cluttered homes with a coat of pastel paint a putting the television in a different corner!
The text of the I Ching is a set of oracular statements represented by 64 sets of six lines each called hexagrams.
"Hexagram": "Hex" is "six". "Gram" is from the Greek "grapho" meaning to write or draw. Therefore, a hexagram is a picture/graphical representation composed of 6 lines. (The Star of David is another example of a hexagram).
In the article above the eight essential forces and structures of the Universe (Heaven - Mountain - Earth - Wind - Fire - Thunder - Water - The Sacred Lake) are shown in relation to the primary eight trigrams that are then combined to produce sixty four variations.
The Yin Yang symbol is an accurate pictorial simplification of the 64 hexagrams of the I Ching. The former shows Yin as the black and Yang as the white. However, it is very important to note that each is shown with the thinnest or smallest part of one becoming equilaterally greater as the other becomes lesser. So, the Yin Yang simplistically illustrates gradients of Yin and Yang. The I Ching hexagrams go much further than that by codifying these gradients into 64 phases. Both represent cyclical change with energies or forces. The Yin Yang particularly illustrates the idea that this all goes around in an endless circle. The I Ching is a means of divination in as much that it agrees with Great Brittan's WW2 leader Winton Churchill who said "If you want to predict what will happen in the future, study the past".
The I Ching is much more than some kind of fortune telling tool that many of us westerners take it to be; it is just one element of a comprehensive and interlocking theory of how internal (personal) and external (world-wide) harmony might be achieved.
I know of many Tai Chi postures or phases of postures that are associated with and in a way, illustrated by I Ching Hexagrams. There are three that are linked to the posture "Beginning". The physical movements of this posture are designed to guide the flow of chi (vital energy) from the feet, up the spine to the top of the head, and then down the front of the body to the abdomen.
Ch'ien/Qien or "Heaven" (hexagram number 1) represents the point at which the knees are straight and the energy has risen up through the spinal column all the way to the head. In the I Ching (the book*) "Ch'ien" is revealed as "Creative Originality" and it suggests that it is time to take action and continue with determination. Work hard but do not overreach.
Fu "Return" or "Turning Point" (hexagram number 24) represents the descent or lowering of chi. In the I Ching "Fu" is revealed as "Returning" and the inference is: You may move freely as there is advantage in all directions with no one opposing you. Keep a firm goal in mind as this is a new cycle of growth - so let things grow. Put behind you the wrong doings of others and they will do the same for you.
K'un or "Earth" (hexagram number 2) represents the outcome of the lowering, in which the energy has moved down to the abdomen. K'un, is revealed as "Fulfilling Destiny" and it is suggested that there is no need to force the issue and that good fortune can be derived from passive compliance.
The oldest method for casting the hexagrams, using yarrow stalks, is a biased random number generator, and because there are more 'old yang' hexagrams than there are old yin' hexagrams the possible answers are not equi-probable. The yarrow stalk method was gradually replaced during the Han Dynasty by the three coins method. Using this method all mathematical imbalances is eliminated. Of course, the fundamental idea underlying this system of divination is that the appropriate answer will be produced, regardless of the probabilities.
There have been several arrangements of the trigrams and hexagrams over the ages. The b? gùa is a circular arrangement of the trigrams, traditionally printed on a mirror, or disk. According to legend, Fu Hsi found the b? gùa on the scales of a tortoise's back.
References: http://en.wikipedia.org/wiki/I Ching.
* The I Ching translated by Rudolf Ritsems and Stephen Karcher. Element ISBN1-85230-536-3