The study of the master-minds of the human race is almost equally instructive in what they achieved and in what they failed to achieve; and speculations which are far from solving the riddle of existence have their use in teaching us why it is insoluble.
Thus it appears that the term Metaphysics has been at different times used in two principal senses: 1. As synonymous with Ontology, to denote that branch of philosophy which investigates the nature and properties of Being or Reality, as distinguished from Phenomenon or Appearance. 2. As synonymous with Psychology, to denote that branch of philosophy which investigates the faculties, operations, and laws of the human mind.
There is a wide application of the term consciousness, in which it is coextensive with the whole cycle of human knowledge; for we can know nothing without being conscious that we know it; and we can investigate no objects but those whose existence, real or apparent, must be made known to us by consciousness. In this sense, what is out of consciousness is out of the field of human knowledge altogether.
But this consideration does not affect the definition which assigns the facts of consciousness as the proper object of metaphysical science. For in other sciences those facts are considered, necessarily indeed, but secondarily only, as the means by which the direct objects of such sciences are made known to us. The manner in which consciousness operates as the instrument of the physical sciences is not taken into account by those sciences, nor is the nature and veracity of its testimony called in question.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the philosophy of consciousness