All existence is the manifestation of the realization(氣化生成) of Gi(氣-Qi in Chinese). In other words, Gi is the principal(主體) followed by its realization and subsequent utilization(有用) in all existence. To man principal(主體) becomes the motivation for life, and utilization(有用) becomes the method needed for living. MyungLiology(命理學), which studies ways to utilize all existence in such way summed up as utilization, proposes ways of living by sorting the uses of all existence into origin-used(喜神) and purpose-used(忌神).
In MyungLiology(命理學), all existence is on earth(地元-in terms of heaven, earth and man), which is the environment in which man lives. In the environment, all existence go by the order of time and the law of life and death. The obligation(司令用神) of man(人元-in terms of heaven, earth and man) underlies the mind that carries out the task bestowed by the heaven and earth. There are two types of method for living, namely origin-used(喜神) and purpose-used(忌神) in which each individual's task is carried out. In carrying out one's task, he/she may make him/herself meritorious by rectifying what has been contorted due to climate change or excess and deficiency of the Five primary substance(or the Five elements). This is called transform-used(有用之神).
In sum, the earth(地元) is the environment for living; the obligation(司令用神) is the given task at birth; the origin-used(喜神) and purpose-used(忌神) signify ways of living toward one's task; the transform-used(有用之神) is the solution for rectifying any contortion.