Matter is a quantitative substance, or that substance which is a constituent of all bodies and in which the physical accident of quantity inheres whereby the body naturally has extended location in space. By reason of this accident of quantity a body is naturally impenetrable, i.e.,occupies space in such a way as to exclude all other bodies from occupying the same space at the same time. Materialism is, then, that philosophic system of Monism which denies the existence of any other kind of substance, such as spirit, and claims that all phenomena of the universe can and must be explained by matter and the forces or energies inherent in and intrinsically dependent upon brute matter.