In the beginning there was energy, and the energy was one. The Taoists called this energy chi.
We live in a universe of duality, however, where the great unity is seemingly broken up into a multiplicity of things, all of which are chi. Think of atomic particles, which are nothing but energy - and at microscopic level everything and everyone is formed of particles.
In keeping with this apparent duality, the Taoists determined that chi was split into two opposing energies - yang, which they deemed the creative, active, masculine, of heaven - and yin, which was determined to be the receptive, passive, nurturing, of the earth and feminine.
The interplay between these two forces gives a picture of the situation facing us at any given moment.
Next they created trigrams, three lines created randomly - each yang or yin - stacked one above the other. The eight variations this could cause each represented a different situation or state of affairs.
By combining two trigrams into a six-line stack or hexagram, it was later discovered that 64 different situations could be portrayed. For example:
This hexagram is composed of the trigram Li above, the trigram representing fire and illumination, and, below it, Sun, the symbol of both wind and wood. So we arrive at the hexagram of Ting - the Cauldron, number 50 in the sequence of 64. Fire and wind together produce heat, a primary requirement for cooking. The cauldron as a whole contains the food being cooked, and is symbolic of the nourishment of wise people who can help advance the conventions and outlook of entire civilisations.
Why a cauldron? Well, the shape of the hexagram helps define its meaning further. The yin line at the beginning represents the cauldron's legs, the three yang lines in 2nd, 3rd and 4th place, are its body, while in the 5th place are the two retaining rings.
The hexagram can be created by any random method, the most common of which is throwing three coins for each of the six lines. The head side of each coin is given a value of three, the tail side a value of two. A sum total of 6 or 8 for the value of the three coins indicates a yin line, and 7 or 9 a yang line.
Moving Lines
A total of 6 or 9 (all three coins tails or all three coins heads) results in a so-called moving line, which in the case of a yin line is marked with a cross in the gap -
and in the case of a yang line with a roundel in its middle -
A moving line indicates a specific meaning within the general situation portrayed by the hexagram. Moreover, it causes the line to change to its opposite - a yang line becomes a yin line, and vice versa.
This of course changes the composition of the hexagram, and creates a new or secondary hexagram which provides an additional aspect to the reading. The changed moving lines of the secondary hexagram are also taken into account in the reading and the interpretation.