 This pattern of thought is further strengthened by Hyegang. In various works, he finally dispenses with Principle for good and promotes Vital Force alone as the ultimate source of reality of the world. He also emphasizes the pragmatic-experimental spirit in our investigation of nature. For Hyegang, Vital Force fills the heaven and earth, i.e., the whole universe. No matter whether it aggregates and disperses, there is nothing that is not Vital Force (Penetration of Spirit and Vital Force (singit’ong 神氣通) Book 1, Sec. 1 in Ch’oe Han’gi Expanded Work, Volume 1). Thus, because of Vital Force that composes it, the whole world is alive and active. However, the most interesting aspect of his idea is that the concept of Principle (i 理) is entirely reduced to Vital Force. For him, Principle means the coherent logical principle (條理) of Vital Force. When Vital Force is invoked, Principle already resides in Vital Force. When Principle is mentioned, Vital Force follows Principle. For this reason, the statement that Principle is one and its manifestations are many (理一分殊), which is one of the common Neo-Confucian interpretations of Principle, is now replaced by the dictum that Vital Force is one and its manifestations are many (氣一分殊).