The problem has thus a twofold aspect, as related to the conditions of being and to the conditions of thought; and its solution may be attempted from the one or the other starting-point. We may commence with abstract principles of being in general, and endeavour to deduce & priori the essential characteristics of existence per se; or we may commence with an examination of the actual constitution of the human mind, and endeavour to ascertain empirically how the conception of reality is formed, and what is its consequent value. And either of these methods of inquiry may be so conducted as in the end to lose sight of the original relation which binds them together; and each may thus present an aspect of irreconcilable antagonism, in place of the mutual pursuit of a common object.
The a priori reasoner may pervert his conception of absolute being into a form which finds, no counterpart in the human consciousness, and, confident in the infallibility of his own process, may condemn as worthless the mirror which refuses to reflect back the distorted image. And the investigator of the facts of consciousness, when his imperfect analysis has failed to discover the hidden element of reality, may proclaim reality itself to be a dream and a delusion, and the mind and all that it contains a mere aggregate of phenomena.
Deceived by the apparent parallelism of the distant rays, the opposing theorists forget that those rays must converge somewhere in a common centre: they forget that philosophy itself is but the articulate development of consciousness; that from consciousness all inquiries set out, and to consciousness they must all return.
And such, history tells us, has been the actual fate of Metaphysics. The clue to its distant mazes, lost almost at the outset of the journey, became more and more irrecoverable as the paths diverged more and more from their common centre; till its latest expositors on both sides were unconscious of its existence.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the Philosophy of Consciousness