The instance of motion, which is commonly made use of to shew after what manner perception depends, as an action, upon its substance, rather confounds than instructs us.

Motion to all appearance induces no real nor essential change on the body, but only varies its relation to other objects.

But betwixt a person in the morning walking a garden with company, agreeable to him; and a person in the afternoon inclosed in a dungeon, and full of terror, despair, and resentment, 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.