The doctrine of Materialism, as formerly taught by Dr. Priestley and his followers, is in some respects similar to that which we have just noticed, but in other respects differs from it, if not in its essential nature, at least in its collateral adjuncts and its practical applications. It resembles the theory of D'Holbach and Comte, in so far as it affirms the doctrine of _unisubstancisme_, and rejects the idea of a _dualism_ such as is implied in the common doctrine of Matter and Spirit. But it differs from that theory, inasmuch as it is combined, whether consistently or otherwise, with the recognition of a personal God, a resurrection from the dead, and a future state of reward and punishment. Dr. Priestley seems to have fluctuated for a time between two opposite extremes,--that of _spiritualizing_ Matter, and that of _materializing_ Mind; for, in a very remarkable passage, we find him saying, "This scheme of _the immateriality of Matter_, as it may be called, or rather, _the mutual penetration of Matter_, first occurred to my friend Mr. Mitchell on reading 'Baxter on the Immateriality of the Soul.'"[149] But at length he settled down in the fixed belief of Materialism, as he had always held the principle of _unisubstancisme_. He held throughout that "Man does not consist of two principles so essentially different from each other as Matter and Spirit, but the whole man is of _one uniform composition_; and that either the material or the immaterial part of the universal system is superfluous."[150] He attempts, therefore, to show, that sensation, perception, and thought,--the common properties of _mind_,--are not incompatible with extension, attraction, and repulsion, which he conceives to be the only essential properties of _matter;_ that both classes of properties may possibly belong to the same subject; and that hence no second substance is necessary to account for and explain any of the phenomena of human nature. In this respect, his theory is precisely the same with that which has been already noticed; but the peculiarity by which it is distinguished from the Atheistic and Antichristian speculations of D'Holbach and Comte is twofold. In the _first_ place, while he ascribes to mere matter the power of sensation, thought, and volition, he admits that these powers, and all others belonging to matter, were communicated to it at the first, and are still continued, by the Divine will, thus recognizing the doctrine both of Creation and Providence; and in the _second_ place, while he denies the natural immortality of the soul, and even the possibility of its conscious existence in a state of separation from the body, he does not deny the immortality of man, but receives it, as well as the doctrine of future rewards and punishments, on the authority of that Divine Revelation which speaks of "the resurrection of the dead," and of "a judgment to come." In these respects, his theory is