The Bagua or Pa Kua are eight symbols used in Taoist cosmology to represent the fundamental principles of reality, seen as a range of eight interrelated concepts. Each consists of three lines, each line either "broken" or "unbroken", respectively representing yin or yang.
It begins with two. There are only 8 ways one can combine them as 3.
5 of the 8 Forces are included in Taoist 5 Element Theory: water, fire, earth, wood, and metal.
The other 3 are: heaven, thunder, and mountain
How can there be five elements in a cosmic description and none of them are air? To someone used to the basic four - fire, water, earth, and air - the concept is confusing.
There are ways to get it. But you have to understand that it's amazing enough to describe everything according to the limitations of the math - 8 trigrams, and doubled into hexagrams, a total of 64 hexagrams with which to describe all the changes.
There are going to have to be some multi-layered meanings. Tui - metal - two solid lines with one broken line at the top - is the perfect example. That trigram represents lake as well as metal. One has to think like a cloud to get all the logic of this. But it has to do with containment. An unobstructed flow like a river or an ocean is much different from a collection point where the earth holds the water like in a lake. Meanwhile, metals are borne from earth. They have a different relationship with water than earth or wood. As well, there is an implication that air is part of Tui. Air is also part of Zun, wind/wood, the other most multi-layered of the 8.
When fire burns wood into ashes, there is no more wood. The ashes are earth. When fire works on metals, it is a weakening but the quality of transformation is much different.
When Zun is wind it symbolizes the penetrating work of the True Gentle. When it is wood it becomes like a tree bursting through the ground from seed or standing on top, one individual growth of wood on a mountain. Coupling them begs the question - what arouses air to become wind? The answer has something to do with how seeds are scattered by the wind and so, with rain and sun, growth occurs. The wind is a basic constituent in the making of plants and trees. And Zun can fuse further - into jade if the cauldron is really exquisite - which is how the I Ching gains depth as one studies the whole system more - while still giving the beginner or intermediate a great deal to work with.
The 8 forces appear in 3 classic orders in a yin/yang bagua. The sequence I was taught is great for applying to how these elements are located in the human body. In future posts I hope to delve into that sequence, perhaps with an illustration. The Taoism and I Ching discussion groups depict them all and more.