In order to explain this matter, I shall just touch upon two principles, one of which shall be more fully explained in the progress of this Treatise; the other has been already accounted for. I believe it may safely be established for a general maxim, that no object is presented to the senses, nor image formed in the fancy, but what is accompanied with some emotion or movement of spirits proportioned to it; and however custom may make us insensible of this sensation, and cause us to confound it with the object or idea, 'twill be easy, by careful and exact experiments, to separate and distinguish them. For, to instance only in the cases of extension and number, 'tis evident that any very bulky object, such as the ocean, an extended plain, a vast chain of mountains, a wide forest; or any very numerous collection of objects, such as an army, a fleet, a crowd, excite in the mind a sensible emotion; and that the admiration which arises on the appearance of such objects is one of the most lively pleasures which human nature is capable of enjoying. Now, as this admiration increases or diminishes by the increase or diminution of the objects, we may conclude, according to our foregoing principles,[7] that 'tis a compound effect, proceeding from the conjunction of the several effects which arise from each part of the cause. Every part, then, of extension, and every unite of number, has a separate emotion attending it when conceived by the mind; and though that emotion be not always agreeable, yet, by its conjunction with others, and by its agitating the spirits to a just pitch, it contributes to the production of admiration, which is always agreeable. If this be allowed with respect to extension and number, we can make no difficulty with respect to virtue and vice, wit and folly, riches and poverty, happiness and misery, and other objects of that kind, which are always attended with an evident emotion. The second principle I shall take notice of is that of our adherence to _general rules_; which has such a mighty influence on the actions and understanding, and is able to impose on the very senses. When an object is found by experience to be always accompanied with another, whenever the first object appears, though changed in very material circumstances, we naturally fly to the conception of the second, and form an idea of it in as lively and strong a manner, as if we had inferred its existence by the justest and most authentic conclusion of our understanding. Nothing can undeceive us, not even our senses, which, instead of correcting this false judgment, are often perverted by it, and seem to authorize its errors.