Generally, epistemology is considered as second degree knowledge, in which the value of knowledge is discussed. On the other hand, in philosophy, the existential characteristics of knowledge, such as separate from matter and its nature, are discussed. But as some contemporary philosophers have mentioned, many epistemological discussions are ontological. Even the discussion of the value of knowledge cannot be without considering its reality. Also, without relying on metaphysical principles, such as the principle of the realization of reality, its having ranks, the principle of causality and its branches, it is not possible to advance epistemological discussions. Therefore, we believe that epistemology is also a first degree knowledge and is a part of ontology, and it is only with a special validity that it can be considered a second degree knowledge.