Indeed, there are few objects, either of perception or conception, which, however close the process of abstraction, do not remain complex in their nature. The simplest forms of matter are _combined_ ideas of extension, figure, color, and relation. These different ideas we gain by the aid of the different senses. Of course, our conceptions are combinations of different qualities in an object which the mind considers as _one_, and as distinct from other objects. Each item, then, in any mental picture is itself a complex object, and each mental picture is formed by a combination of such complex objects. It will be found very difficult, if not impossible, to mention a name which recalls any object of sense in which the conception recalled by the word is a single disconnected thing, without any idea of place or any attendant circumstances, and, as before remarked, almost all objects of sense are complex objects, combining several ideas, which were gained through the instrumentality of different senses. The idea of color is gained by one sense, of position, shape, and consistency by another, and other qualities and powers which the mind associates with it by other senses. The other fact necessary to the correct understanding of the subject is the influence which the _desires_ and _emotions_ have upon the character both of the perceptions and conceptions with which they coexist. It will be found that our _sensations_ vary in vividness and distinctness according to the strength and permanency of certain feelings of desire which coexist with them. For example, we are continually hearing a multitude of sounds, but in respect to many of them, as we feel no desire to know the cause or nature of them, these sensations are so feeble and indistinct as scarcely ever to be recalled to the mind or recognized by any act of memory; but should we hear some strange wailing sound, immediately the desire would arise to ascertain its nature and cause. It would immediately become an object of distinct and vivid perception, and continue so as long as the desire lasted. While one sensation becomes thus clear and prominent, it will be found that other sensations which were coexisting with it will become feebler and seem to die away. The same impressions may still be made upon the eye as before, the same sounds that had previously been regarded may still strike upon the ear, but while the desire continues to learn the cause of that strange wailing sound, the other sensations would all be faint and indistinct. When this desire is gratified, then other sensations would resume their former distinctness and prominency.