Objectivism and theories of concepts underly cognition and measurement. Since its all in a constant perceptual stage, i agree that we must explore much of the limitations of knowledge. Essence to me is epistemological. Some of these concepts in earlier philosophies rose through arbitrary meanings. Some abstractions again, at some point became Axiomatic concepts. Something that is perceived directly but grasped conceptually are to different things. To identify them consciously and self consciously as an epistemological need can be a very ambiguous endeavor.