The mind is continually under the influence of some desire. It constantly has some plan to accomplish, some cause to search out, or some gratification to secure. The present wish or desire of the mind imparts an interest to whatever conception seems calculated to forward this object. Thus, if the mathematician has a problem to solve, and this is the leading desire of the mind, among the various conceptions that arise, those are the most interesting which are fitted to his object, and such immediately become vivid and distinct. If the painter or the poet is laboring to effect some new creation of his art, and has this as the leading object of desire, whatever conceptions seem best fitted to his purpose are immediately invested with interest, and become distinct and clear. If the merchant, or the capitalist, or the statesman has some project which he is toiling to accomplish, whatever conceptions appear adapted to his purpose soon are glowing and defined, in consequence of the interest with which desire thus invests them.

From this it appears that the nature of the desire, or governing purpose of the mind, will in a great measure determine the nature and the succession of its conceptions. If a man has chosen to find his chief happiness in securing power and honor, then those conceptions will be the most interesting to his mind that best fall in with his object. If he has chosen to find happiness in securing the various gratifications of sense, then those conceptions that most coincide with this desire will become prominent. If a man has chosen to find his chief enjoyment in doing the will of God, then his conceptions will, to a great extent, be conformed to this object of desire. The current of a man's thoughts, therefore, becomes the surest mode of determining what is the governing purpose or leading desire of the mind.

But there are seasons in our mental history when the mind does not seem to be under the influence of any governing desire; when it seems to relax, and its thoughts appear to flow on without any regulating principle. At such times the vividness of leading conceptions, which otherwise is determined by desire, seems to depend upon our past experience. Those objects which, in past experience, have been associated with emotion, are those which the mind selects, and which thus begin to glow in the distinct lineaments with which emotion at first invested them.

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.

The first is, that those objects are most likely to attend each other which in past experience were united, while some strong emotion was existing with them. If, for example, a retired lake had been the scene of death to a beloved friend, the conception of this object would be almost invariably associated with the image of the friend that had perished beneath its waters, and also with the scene of his death. In like manner, if some friend had expired at a certain hour of the day, or on a particular day of the year, the return of these seasons would probably be associated with the sorrowful scenes connected with them in past experience.

The second law of association is, that long continued or frequently repeated attention to objects that are connected at the time of this attention will secure the connected return of these objects. Attention, it may be recollected, is desire united with our conceptions, thus rendering them more vivid.

It seems to produce the same effect if this attention is long continued or if it is frequently repeated. Thus, if the mind has dwelt for a long time on a beautiful picture, has noticed all its proportions, its shading, its outline, and its colors with minute attention, one object in this picture can not recur to the mind without bringing with it the other objects that were associated at the time of this close attention. The frequent repetition of a sentence is a case where oft repeated though short attention to certain words has the effect of recalling them to the mind in the connection in which they were placed during this repeated attention.