They had recourse to the theory of Materialism chiefly with the view of excluding a world of spirits, and of undermining the doctrine of a future state: here it is applied to prove the constant development and indestructible existence of minds generated from matter, but destined to survive the dissolution of the body; nay, every particle of matter in the universe is supposed to be advancing, in one magnificent progression, towards the spiritual state.

The danger now is, not that Religion may be undermined by Materialism, but that it may be supplanted by a fond and foolish superstition, in which the facts of Mesmerism and the fictions of Clairvoyance are blended into one ghostly system, fitted to exert a powerful but pernicious influence on over-credulous minds.[152] On a review of the various forms which the theory of Materialism has assumed, it must be evident that we should be doing great injustice to their respective advocates, did we place them all on the same level in relation to Theology, or pronounce upon them one indiscriminate censure.
In the hands of D'Holbach and Comte, it was associated with the avowal of Atheism, and the denial of a future state: in the hands of Priestley, it was associated with the recognition of a God, and the Christian doctrine of a resurrection: in the hands of Dr.Good, it was combined with the principles of Theism, and even with the revealed doctrine of the separate existence of the soul during the interval between death and the resurrection: and in the hands of Davis and the author of the "Purpose of Existence," it is exhibited in connection with a theory of Progression, widely different, indeed, from the doctrine of Scripture, but equally different from the infidel speculations of the last century.
Still, with all these shades of difference, there is _that common to all_ the forms in which it can be presented which shows that they are radically one and the same: _they all deny the existence of any generic difference between Matter and Mind_.
Confining our attention to this common element, and omitting the consideration of minor diversities, we may now inquire into the grounds on which the theory rests, and the most plausible reasons which have been urged in support of it.
To some minds it has been recommended by its _apparent simplicity_.

It speaks only of _one_ substance as existing in Nature under various modifications.

It represents the universe, so far as created being is concerned, as entirely composed of _matter_, more or less refined; and thus excludes the complication which must necessarily arise from the supposition of two substances, generically different, yet intimately and indissolubly related.

The principle, therefore, which prompts us to seek unity in diversity, and to reduce, by some comprehensive generalization, a multitude of phenomena under one general law, has led some to adopt the theory of _unisubstancisme_ in preference to the opposite doctrine of _dualism_.