When we infer the existence of an object from that of others, some object must always be present either to the memory or senses, in order to be the foundation of our reasoning; since the mind cannot run up with its inferences IN INFINITUM.

Reason can never satisfy us that the existence of any one object does ever imply that of another; so that when we pass from the impression of one to the idea or belief of another, we are not determined by reason, but by custom or a principle of association.

But belief is somewhat more than a simple idea.

It is a particular manner of forming an idea: And as the same idea can only be varyed by a variation of its degrees of force and vivacity; it follows upon the whole, that belief is a lively idea produced by a relation to a present impression, according to the foregoing definition.] This operation of the mind, which forms the belief of any matter of fact, seems hitherto to have been one of the greatest mysteries of philosophy; though no one has so much as suspected, that there was any difficulty in explaining it.

For my part I must own, that I find a considerable difficulty in the case; and that even when I think I understand the subject perfectly, I am at a loss for terms to express my meaning.