The perception of a material universe, as it is the most prominent fact of cognition, so has it given rise to the problem which has been most agitated by philosophers. This question does not relate to the existence of the fact. The existence of the perception of matter is admitted on all hands. It refers to the nature, or origin, or constitution of the fact. Is the perception of matter simple and indivisible, or is it composite and divisible? Is it the ultimate, or is it only the penultimate, _datum_ of cognition? Is it a relation constituted by the concurrence of a mental or subjective, and a material or objective element,--or do we impose upon ourselves in regarding it as such? Is it a state, or modification of the human mind? Is it an effect that can be distinguished from its cause? Is it an event consequent on the presence of real antecedent objects? These interrogations are somewhat varied in their form, but each of them embodies the whole point at issue, each of them contains the cardinal question of philosophy. The perception of matter is the admitted fact. The _character_ of this fact--that is the point which speculation undertakes to canvass, and endeavours to decipher. Another form in which the question may be put is this: We all believe in the existence of matter--but what _kind_ of matter do we believe in the existence of? matter _per se_, or matter _cum perceptione_? If the former--this implies that the given fact (the perception of matter) is compound and submits to analysis; if the latter--this implies that it is simple and defies partition. Opposite answers to this question are returned by psychology and metaphysics. In the estimation of metaphysic, the perception of matter is the absolutely elementary in cognition, the _ne plus ultra_ of thought. Reason cannot get beyond, or behind it. It has no pedigree. It admits of no analysis. It is not a relation constituted by the coalescence of an objective and a subjective element. It is not a state or modification of the human mind. It is not an effect which can be distinguished from its cause. It is not brought about by the presence of antecedent realities. It is positively the FIRST, with no forerunner. The perception-of-matter is one mental word, of which the verbal words are mere syllables. We impose upon ourselves, and we also falsify the fact, if we take any other view of it than this. Thus speaks metaphysic, though perhaps not always with an unfaltering voice.