Nevertheless it may be known, insofar as consciousness may be self-aware. Let us begin by distinguishing the epistemological from ontological grounding. It should be self-evident that nothing may be known apart from consciousness, in some sense, so consciousness serves as epistemological ground. Realism, the position that we discover how things are in themselves because consciousness merely records reality without determining it, can never be more than a naive assumption. However, here we must also be careful not to reduce being to existence.
Existence is phenomenal, referring to how a thing appears to consciousness.
Being is noumenal, referring to the way in which a thing appears as not reducible to its appearance. This provides phenomenological grounds for rejecting subjective idealism. The world includes far more than those things that are actually being observed at a particular time. It would be ridiculous to claim that there is presently no far side of the moon, or even that we never knew that there was a far side of the moon until it was observed. Moreover, if we wish to preserve intellectual integrity, Berkeley's appeal to the omnivigilant mind of God to preserve the existence of everything that we are not perceiving is not a resource to which we may appeal.