The original concept of yin and yang came from the observation of nature and the environment. “Yin” originally referred to the shady side of a slope while “yang” referred to the sunny side. Later, this thinking was used in understanding other things, which occurred in pairs and had complementary and opposing characteristics in nature. Some examples include: sky and earth, day and night, water and fire, active and passive, male and female and so on. Working with these ideas, ancient people recognized nearly all things could have yin and yang properties. Yin and yang can describe two relative aspects of the same phenomena such as the example of the slope, or they can describe two different objects like sky and earth.