The question of what ontologically exists is of upmost importance and fundamental in answering any question about what is to be epistemological known. The problem is its circularity, that we can only “guess” at what exists from what is known.
The nature of knowledge, then, must tell us something of the nature of what exists, that is, we can never “know” something else directly. If we were to know something else directly then we would be that thing. Then, we would not be something else. Things are necessarily separate and never known directly.
This also tells us about the nature of knowledge – that a medium is always necessary in order to have knowledge of it. This is true of both self-knowledge (or will) and other-knowledge (or representation) where they both are indirect. The internal (self) medium is no different to the external (other) medium. They only differentiations in degrees of knowledge and levels of activity or process.