That is what makes it axiomatic. Existence is grasped perceptually - open your eyes and what you see is part of existence. It is the total of all that exists . The word reality is often used for existence in the sense all which exists . Consciousness is the faculty of awareness.
Awareness implies awareness of something .
We are aware of reality around us, through perception. The three axioms together - existence , consciousness and identity establish the primacy of existence . Consciousness has the power to apprehend reality, not to create it. What is Epistemology Epistemology is the science of the proper methods used to acquire and validate one's conclusions about reality and give them the status of knowledge . Since existence is primary, the contents of one's mind - thoughts, ideas, emotions, etc.