ment, there seems to be
a radical difference, and of quite another kind, than what is produced
on a body by the change of its situation. As we conclude from the
distinction and separability of their ideas, that external objects
have a separate existence from each other; so when we make these ideas
themselves our objects, we must draw the same conclusion concerning
them, according to the precedent reasoning. At least it must be confest,
that having idea of the substance of the soul, it is impossible for us
to tell how it can admit of such differences, and even contrarieties of
perception without any fundamental change; and consequently can never
tell in what sense perceptions are actions of that substance. The use,
therefore, of the word, action, unaccompanyed with any meaning, instead
of that of modification, makes no addition to our knowledge, nor is of
any advantage to the doctrine of the immateriality of the soul.

I add in the second place, that if it brings any advantage to that
cause, it must bring an equal to the cause of atheism. For do our
Theologians pretend to make a monopoly of the word, action, and may not
the atheists likewise take possession of it, and affirm that plants,
animals, men, &c. are nothing but particular actions of one simple
universal substance, which exerts itself from a blind and
absolute necessity? This you'll say is utterly absurd. I own it is
unintelligible; but at the same time assert, according to the principles
above-explained, that it is impossible to discover any absurdity in the
supposition, that all the various objects in nature are actions of
one simple substance, which absurdity will not be applicable to a like
supposition concerning impressions and ideas.

From these hypotheses concerning the substance and local conjunction of
our perceptions, we may pass to another, which is more intelligible
than the former, and more important than the latter, viz. concerning the
cause of our perceptions. Matter and motion, it is commonly said in the
schools, however varyed, are still matter and motion, and produce only
a difference in the position and situation of objects. Divide a body as
often as you please, it is still body. Place it in any figure, nothing
ever results but figure, or the relation of parts. Move it in any
manner, you still find motion or a change of relation. It is absurd to
imagine, that motion in a circle, for instance, should be nothing but
merely motion in a circle; w