The doctrine of Materialism has assumed several distinct phases or forms in the hands of its different advocates; and these must be carefully discriminated from each other, if we would either estimate aright their respective merits, or do justice to the parties by whom they have been severally maintained. The grossest and most revolting form of Materialism is that which _identifies mind with matter_, and _thought with motion_. It denies that there is any real or radical difference between physical and moral phenomena, and affirms that life and thought are so entirely dependent on material organization, that the dissolution of the body must necessarily be the destruction of conscious existence, and that death can only be an eternal sleep. This is the doctrine of Materialism which was taught in a former age, by the author of the "Systeme de la Nature," and which has recently been revived by M. Comte in France, and by Atkinson and Martineau in England. A few extracts will sufficiently illustrate its character and tendency. "Men have evidently abused the distinction," says Baron D'Holbach, "which is so often made between _man physical_ and _man moral_: man moral is nothing else than that physical being considered in a certain point of view, that is, with reference to some modes of action which belong to his peculiar organization."--"The universe--that vast assemblage of everything that exists--exhibits nowhere anything else than _matter and motion_."--"If we are asked, what is man? we reply, that he is a material being, organized or framed so as to feel, to think, and to be affected in certain ways peculiar to himself, according to his organization."[147] More recently, M. Comte has affirmed that "the subject of all our researches is _one_," and that "all natural phenomena are the necessary results either of the laws of extension or of the laws of motion;" while M. Crousse is quite clear that "intelligence is a property or effect of matter," and that "body and spirit together constitute matter." In our own country, Atkinson and Martineau have not shrunk from the avowal of the same doctrine, or the adoption of the most revolting consequences that can be deduced from it. "Instinct, passion, thought, are effects of organized substances."--"Mind is the consequence or product of the material man; it is not a thing having a seat or home in the brain, but it is the manifestation or expression of _the brain in action,_ as heat and light are of fire, and fragrance of the flower."[148]