“ MATERIALISM (from Lat. materia, matter) , in philosophy, the theory which regards all the facts of the universe as explainable in terms of matter and motion, and in particular explains all psychical processes by physical and chemical changes in the nervous system. It is thus opposed both to natural realism and to idealism. For the natural realist stands upon the common-sense position that minds and material objects have equally effective existence; while the idealist explains matter by mind and denies that mind can be explained by matter. ”

“ The various forms into which materialism may be classified correspond to the various causes which induce men to take up materialistic views. Naïve materialism is due to a cause which still, perhaps, has no small power, the natural difficulty which persons who have had no philosophic training experience in observing and appreciating the importance of the immaterial facts of consciousness. The pre-Socratics may be classed as naïve materialists in this sense ”

“ Cosmological materialism is that form of the doctrine in which the dominant motive is the formation of a comprehensive world-scheme: the Stoics and Epicureans were cosmological materialists. In anti-religious materialism the motive is hostility to established dogmas which are connected, in the Christian system especially, with certain forms of spiritual doctrine. ”