I have often observed, that, beside cause and effect, the two relations of resemblance and contiguity are to be considered as associating principles of thought, and as capable of conveying the imagination from one idea to another. I have also observed, that when of two objects, connected together by any of these relations, one is immediately present to the memory or senses, not only the mind is conveyed to its co-relative by means of the associating principle, but likewise conceives it with an additional force and vigour, by the united operation of that principle, and of the present impression. All this I have observed, in order to confirm, by analogy, my explication of our judgments concerning cause and effect. But this very argument may perhaps be turned against me, and, instead of a confirmation of my hypothesis, may become an objection to it. For it may be said, that if all the parts of that hypothesis be true, viz. _that_ these three species of relation are derived from the same principles; _that_ their effects, in enforcing and enlivening our ideas, are the same; and _that_ belief is nothing but a more forcible and vivid conception of an idea; it should follow, that that action of the mind may not only be derived from the relation of cause and effect, but also from those of contiguity and resemblance. But as we find by experience that belief arises only from causation, and that we can draw no inference from one object to another, except they be connected by this relation, we may conclude, that there is some error in that reasoning which leads us into such difficulties. This is the objection: let us now consider its solution. 'Tis evident, that whatever is present to the memory, striking upon the mind with a vivacity which resembles an immediate impression, must become of considerable moment in all the operations of the mind, and must easily distinguish itself above the mere fictions of the imagination. Of these impressions or ideas of the memory we form a kind of system, comprehending whatever we remember to have been present, either to our internal perception or senses; and every particular of that system, joined to the present impressions, we are pleased to call a _reality_. But the mind stops not here. For finding, that with this system of perceptions there is another connected by custom, or, if you will, by the relation of cause or effect, it proceeds to the consideration of their ideas; and as it feels that 'tis in a manner necessarily determined to view these particular ideas, and that the custom or relation, by which it is determined, admits not of the least change, it forms them into a new system, which it likewise dignifies with the title of _realities_. The first of these systems is the object of the memory and senses; the second of the judgment.