'Cheon' is one of four categories with 'Ki'(氣), 'Do'(道), ‘Ri'(理). Specially 'Cheon' meaned sky is so important that most of philosophers have referred to it. 'Cheon' is widespread, so it has been the object of the astronomers and subject of the philosophers. All recognize the conception definitely and consistently, in the other hand some vaguely, someone give different conceptions. Therefore this paper is written with a view to right recognition of the conception and relationships with the human by the study of significance changes by the times.

Ki is the important conception of Chinese philosophy, many of philosophers have discussed it. So the meaning of it is various in accordance with the times and the scholars. And it has been discussed not only in the sphere of philosophy but medicine, astronomy, g eography, society and culture ; therefore we can't understand the Oriental studies without the comprehension of it. Above all, the Oriental-medicine is based on the principles of it, that is to say 'Ki-medicine'. There are Ki of a letter, Ki of a philosophy, Ki of a nature and Ki of the human body according to the recognition process from that time on the ancient. This paper is written with the view of the right understanding about it by the comparison of various theories dealed with it.