We have two basic works of-his: “On the Divine Names”, : and “On the Hierarchies.” The latter book is divided into the Heavenly and the ecclesiastical hierarchies. The word “hierarchy” probably was created by him; at least we don’t know if anyone else used it before. It is derived. from hieros, holy, sacred; and arch principle, power, beginning, etc. – thus, a holy power. The word hierarchy is defined by him as a holy system of degrees with respect to knowledge and efficacy This characterizes .all Catholic thinking very much; i. t., it is not only ontological, but also epistemological; there are degrees not only in being but also in knowledge.