deas;
though by their force and settled order, arising from custom and the
relation of cause and effect, they distinguish themselves from the other
ideas, which are merely the offspring of the imagination.

As to the influence of contiguity and resemblance, we may observe, that
if the contiguous and resembling object be comprehended in this system
of realities, there is no doubt but these two relations will assist that
of cause and effect, and infix the related idea with more force in the
imagination. This I shall enlarge upon presently. Mean while I shall
carry my observation a step farther, and assert, that even where the
related object is but feigned, the relation will serve to enliven the
idea, and encrease its influence. A poet, no doubt, will be the better
able to form a strong description of the Elysian fields, that he prompts
his imagination by the view of a beautiful meadow or garden; as at
another time he may by his fancy place himself in the midst of these
fabulous regions, that by the feigned contiguity he may enliven his
imagination.

But though I cannot altogether exclude the relations of resemblance and
contiguity from operating on the fancy in this manner, it is observable
that, when single, their influence is very feeble and uncertain. As the
relation of cause and effect is requisite to persuade us of any real
existence, so is this persuasion requisite to give force to these other
relations. For where upon the appearance of an impression we not
only feign another object, but likewise arbitrarily, and of our mere
good-will and pleasure give it a particular relation to the impression,
this can have but a small effect upon the mind; nor is there any reason,
why, upon the return of the same impression, we should be determined to
place the same object in the same relation to it. There is no manner of
necessity for the mind to feign any resembling and contiguous objects;
and if it feigns such, there is as little necessity for it always to
confine itself to the same, without any difference or variation. And
indeed such a fiction is founded on so little reason, that nothing but
pure caprice can determine the mind to form it; and that principle being
fluctuating and uncertain, it is impossible it can ever operate with
any considerable degree of force and constancy. The mind forsees and
anticipates the change; and even from the very first instant feels the
looseness of its actions, and the weak hold it has of it