bodies operate on each other: Their force or energy is entirely
incomprehensible: But are we not equally ignorant of the manner or force
by which a mind, even the supreme mind, operates either on itself or on
body? Whence, I beseech you, do we acquire any idea of it? We have no
sentiment or consciousness of this power in ourselves. We have no idea
of the Supreme Being but what we learn from reflection on our own
faculties. Were our ignorance, therefore, a good reason for rejecting
any thing, we should be led into that principle of denying all energy in
the Supreme Being as much as in the grossest matter. We surely
comprehend as little the operations of one as of the other. Is it more
difficult to conceive that motion may arise from impulse than that it
may arise from volition? All we know is our profound ignorance in
both cases[15].

[15] I need not examine at length the _vis inertiae_ which is
so much talked of in the new philosophy, and which is ascribed
to matter. We find by experience, that a body at rest or in
motion continues for ever in its present state, till put from
it by some new cause; and that a body impelled takes as much
motion from the impelling body as it acquires itself. These are
facts. When we call this a _vis inertiae_, we only mark these
facts, without pretending to have any idea of the inert power;
in the same manner as, when we talk of gravity, we mean certain
effects, without comprehending that active power. It was never
the meaning of Sir ISAAC NEWTON to rob second causes of all
force or energy; though some of his followers have endeavoured
to establish that theory upon his authority. On the contrary,
that great philosopher had recourse to an etherial active fluid
to explain his universal attraction; though he was so cautious
and modest as to allow, that it was a mere hypothesis, not to