Yin & Yang
Yin and Yang subdivides all the phenomena of nature, all the energy and all the organs of the body into two groups. Yin and yang are not absolute but instead describe conditions that are relative and dynamic. Yin mechanisms or structures are related with the interior. They absorb and collect energy. Yang, however, projects outwards and upwards, with a tendency to exhaust itself. Only in the perfect harmony of Yin and Yang can Qi flourish and flow freely.