 On the other hand, Vital Force (gi, C. qi 氣) is a psycho-physical force or energy that can serve as the vehicle of Principle. As concretizing force, it is the primordial stuff out of which everything in the universe is made. Following Zhu Xi in Song China, the Neo-Confucians at the time typically believed that Principle can manifest itself in the world only by means of Vital Force. When Principle is manifested in the spatiotemporal world by Vital Force, it becomes material (chil 質). The material then refers to the state of Vital Force’s becoming thick and dense. Thus, Principle is the same everywhere but Vital Force is exemplified in different modes or qualities. For example, Vital Force freely moves when it is refined, but it is inert when it is coarse.