Metaphysics has been defined by Aristotle (and the definition may be for the present provisionally accepted) as the science which contemplates being as being, and the attributes which belong to it as such. The latter definition, while verbally resembling the former, exhibits, in fact, an important modification of it; for it implies that the progress of philosophy had necessitated the division of things in general into beings, or things as they are, and phenomena, or things as they appear.
The material principles assumed by the Ionians, and the mathematical relations of the Pythagoreans, were theories of the universe, falling under the general conception of Philosophy; but the origin of Metaphysics must rather be dated from the period when the Eleatics denied the reality of the sensible world, and confined the region of truth to the supersensible unity which can be obtained only by contemplation.
The first step towards a definite conception of Metaphysics was attained by regarding it as the science of real existence. But this conception, like the wider one of Philosophy in general, becomes in its subsequent process developed from different and even contradictory points of view, till the resulting systems appear to have nothing in common but the name.
The notion of bang, as distinguished from phenomenon, corresponds in its original signification with that which the mind conceives as permanent and unchangeable, in opposition to that which is regarded as transitory and fluctuating. Such an object of inquiry may be approached from two opposite sides. It is the real in itself, and it is contemplated by the mind as such.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or or the Philosophy of Consciousness