The comparisons employed by poets and orators, coincide with the last-mentioned supposition. It is always a known object that is to be aggrandized or lessened. The former is effectuated by likening it to some grand object, or by contrasting it with one that has the opposite character. To effectuate the latter, the method must be reversed. The object must be contrasted with something superior to itself, or likened to something inferior. The whole effect is produced upon the principal subject, which by this means is elevated above its rank or depressed below it. In accounting for the effect that any unusual resemblance or contrast has upon the mind, I have hitherto assigned no other cause but surprise; and to prevent confusion and obscurity, I thought it proper to discuss that principle first. But surprise is not the only cause of the effect described. Another cause concurs, which operates perhaps not less powerfully than surprise. This cause is a principle in human nature that lies still in obscurity, not having been evolved by any writer, though its effects are extensive. As it is not distinguished by a proper name, the reader must be satisfied with the following description. No man who studies himself or others but must be sensible of a tendency or propensity in the mind to complete every work that is begun, and to carry things to their full perfection. This principle has little opportunity to display itself upon natural operations, which are seldom left imperfect. But in the operations of art it hath great scope; and displays itself remarkably, by making us persevere in our own work, and by making us wish for the completion of what is done by another. We feel a sensible pleasure when the work is brought to perfection; and our pain is not less sensible when we are disappointed. Hence our uneasiness, when an interesting story is broke off in the middle, when a piece of music ends without a close, or when a building or garden is left imperfect. The same principle operates in making collections, such as the whole works good and bad of any author. A certain person endeavoured to collect prints of all the capital paintings, and succeeded except as to a few. La Bruyere remarks, that an anxious search was made for these, not on account of their value, but to complete the set[82]. The final cause of this principle is an additional proof of its existence. Human works are of no significancy till they be completed. Reason is not always a sufficient counterbalance to indolence: and some principle over and above is necessary, to excite our industry, and to prevent our stopping short in the middle of the course.