Five Elements
The basic theory behind the 5 Elements is there are “different kinds” of qi in nature. In Chinese Traditional Medicine, or Oriental Medicine, they are represented as water, wood, fire, earth, and metal. These five represent a class of qi which takes many forms. See the 5 element chart for more information.
One way they interact is that one will feed to the next one. For example, starting with water, the essential for life as we know it, it allows for wood to grow, and wood is the fuel for fire to burn, the burned wood turns to earth, metal is found in earth, and water condenses on metal. Then, the cycle is back at water. This is called inter-promoting. It is also known as a parent/child relationship. Water is the parent of wood, so the qi of water is passed down to give nutrients to wood. Wood promotes fire, fire promotes earth, earth promotes metal, and metal promotes water. In inter-promoting, yin always promotes yin and yang always promotes yang.
Then, there is the connection between the elements that keep others in check. Look at the diagram the star in the middle of the circle is the inter-restraining. For example, when the water qi gets too strong, something has to bring it back in line so the rest of the elements are balanced. Earth will restrain water. From this example, extend it to all the elements: water restrains fire, wood restrains earth, fire restrains metal, earth restrains water, and metal restrains wood. And the way to remember it is water puts out fire, trees (wood) keeps the ground/dirt (earth) from being blown in the wind or washed away in a flood, fire melts metal to be shaped, earth is used to create dams, and metal axes cut down the trees.
On the chart below, you will see that there is an organ section to the list. There are yin and yang organs. The job of the yin organs is to transform. For example, the lungs transform oxygen to carbon dioxide. And the job of the yang organs is to transport. The stomach is part of the transportation of food through the body from eating to going to the restroom.
As the diagram shows, the yin organs feed/promote the yin organs, and yang organs feed/promote the yang organs: the inter-promoting cycle of the 5 elements. And the inter-retraining, the yang organs restrain the yin organs, and the yin organs restrain the yang organs. In these two relationships, qi is always cycling, moving, living. Also, when the cycle becomes unbalanced, the qi can be restored to balance by enhancing or lowering one or more element qi. This theory of balance is studied and used in the treatments by TCM/Oriental Medicine doctors.