past appearance to the senses, but are not able to observe this connexion to be perfectly constant, since the turning about of our head, or the shutting of our eyes is able to break it. What then do we suppose in this case, but that these objects still continue their usual connexion, notwithstanding their apparent interruption, and that the irregular appearances are join'd by something, of which we are insensible? But as all reasoning concerning matters of fact arises only from custom, and custom can only be the effect of repeated perceptions, the extending of custom and reasoning beyond the perceptions can never be the direct and natural effect of the constant repetition and connexion, but must arise from the co-operation of some other principles.
I have already[1] observ'd, in examining the foundation of mathematics, that the imagination, when set into any train of thinking, is apt to continue, even when its object fails it, and like a galley put in motion by the oars, carries on its course without any new impulse. This I have assign'd for the reason, why, after considering several loose standards of equality, and correcting them by each other, we proceed to imagine so correct and exact a standard of that relation, as is not liable to the least error or variation. The same principle makes us easily entertain this opinion of the continu'd existence of body. Objects have a certain coherence even as they appear to our senses; but this coherence is much greater and more uniform, if we suppose the objects to have a continu'd existence; and as the mind is once in the train of observing an uniformity among objects, it naturally continues, till it renders the uniformity as compleat as possible. The simple supposition of their continu'd existence suffices for this purpose, and gives us a notion of a much greater regularity among objects, than what they have when we look no farther than our senses.
But whatever force we may ascribe to this principle, I am afraid 'tis too weak to support alone so vast an edifice, as is
- ↑ Part II. sect. 4.
