physical impulse; if intellectual thought could be reduced to material
motion; if desire and aversion, hope and fear could be explained by the
natural laws of attraction and repulsion, then we might blend the two
substances into one, and speak of "mind" as a mere modification of
"matter." But as long as the properties or powers by which alone any
substance can be known are seen to be generically different, we cannot
confound the substances themselves, or reduce them to one category,
without violating the plainest rules of philosophical inquiry.

And yet to these rules Dr. Priestley refers, as if they warranted the
conclusions at which he had arrived. He desires his readers "to recur to
the universally received rules of philosophizing, such as are laid down
by Sir Isaac Newton at the beginning of his third book of "Principia."
The first of these rules, as laid down by him, is that we are to _admit
no more causes than are sufficient to explain appearances_; and the
second is, that to _the same effect_ we must, as far as possible, assign
_the same cause_." We cheerfully accept these canons of philosophical
inquiry; and it is just because no one substance is sufficient, in our
estimation, to account for _all_ the appearances, that we equally reject
the "spiritualism" of Berkeley, who would resolve all phenomena into
"mind," and the "materialism" of Priestley, who would resolve all
phenomena into "matter." Matter and Mind may, indeed, be said to
resemble each other in some respects,--in their being equally existent,
equally created, and equally dependent; but their essential properties
are generically different, for there is no identity, but a manifest and
undeniable diversity, between thought, feeling, desire, volition, and
conscience, and the various qualities or powers belonging to matter,
such as extension, solidity, and _vis inertiae_, or even the powers of
attraction and repulsion. On the ground of this manifest difference
between the properties by which alone any substance makes itself known,
we hold ourselves warranted to affirm that the "mind" is immaterial, and
to ascribe mental phenomena to a _distinct substantive being_, not less
than the material phenomena of Nature.

Some ingenious thinkers, on both sides of the question, have not been
fully satisfied with this method of stating the grounds of our opinion.
It has been said by our opponents, that if we found merely on the
acknowledged difference between two se