In past experience, all conceptions which were attended with emotion were most distinct and clear, and therefore, when such conceptions return united with others, they are the ones which are most interesting, and thus most vivid and distinct. Thus, in our musing hours of idle reverie, as one picture after another glides before the mind, if some object occurs, such as the home of our youth, or the friend of our early days, the emotions which have so often been united with these objects in past experience cause them to appear in clear and glowing lineaments, and the stronger have been the past emotions connected with them, the more clearly will they be defined. It appears, then, that there are two circumstances that account for the apparent _selection_ which the mind makes in its objects of conception. The first is the feeling that _certain conceptions are fitted to accomplish the leading desire of the mind_; and the second is, that _certain objects in past experience have been attended with emotion_. But there is another phenomenon in our mental history which has a direct bearing on the nature and succession of our conceptions. When any conception, through the influence of desire or emotion, becomes the prominent object, immediately other objects with which this has been associated in past experience begin to return and gather around it in new combinations. Thus a new picture is presented before the mind, from which it again selects an object according as desire or emotion regulates, which, under this influence, grows vivid and distinct. Around this new object immediately begin to cluster its past associates, till still another scene is fresh arrayed before the mind. In these new combinations, those objects which are least interesting continually disappear, while those most interesting are retained to form a part of the succeeding picture. Thus, in every mental picture, desire or emotion seems to call forth objects which start out, as it were, in bold relief from all others, and call from the shade of obscurity the companions of their former existence, which gather around them in new and varied combinations. Almost every object of thought in past experience has been connected with a great number of other objects, and so great has been the variety of its former combinations, that it would be impossible to predict, with any degree of certainty, _which_ of its past associates will be summoned to aid in forming the new mental scenes which are destined to arise. Yet experience has enabled us to detect some _general laws_, which appear to regulate these combinations.