Perception is _par excellence_ the faculty of cognising the concrete. It strives to embrace all the qualities of its object without completely succeeding, because it is held in check by an internal foe,—the natural tendency of the mind to simplify and to eliminate. The same horse, at a given moment, is not perceived in the same manner by a jockey, a veterinary surgeon, a painter, and a tyro. To each of these, certain qualities, which vary individually, stand in relief, and others recede into the background. Except in cases of methodical and prolonged investigation (where we have observation, and not perception) there is always an unconscious selection of some principal characteristics which, grouped together, become a substitute for totality. It must not be forgotten that perception is pre-eminently a _practical_ operation, that its mainspring is interest or utility, and that in consequence we neglect—i. e., leave in the field of obscure consciousness—whatever at the moment concerns neither our desires nor our purposes. It would be superfluous to review all the forms of perception (visual, auditory, tactile, etc.), and to show that they are governed by this same law of utility; but it should be remarked that the natural mechanism by which the strengthened elements and the weakened elements are separated, is a rude cast of what subsequently becomes abstraction, that the same forces are in play, and are ultimately reducible to some definite direction given to the attention. With the image, the intermediate stage between percept and concept, the reduction of the object represented to a few fundamental features is still more marked. Not merely is there among the different representations which I may have of some man, dog, or tree, one that for the time being necessarily excludes the others (my oak tree perforce appears to me in summer foliage, tinted by autumn, or bereft of leaves,—in bright light or in shade), but even this individual, concrete representation which prevails over the others is no more than a sketch, a reduction of reality with many details omitted. Apart from the exceptionally gifted men in whom mental vision and mental audition are perfect, and wholly commensurate (as it would seem) with perception, the representations which we call exact are never so, except in their most general features. Compare the image we have with our eyes closed of a monument, with the perception of the monument itself; the remembrance of a melody with its vocal or instrumental execution. In the average man, the image, the would-be copy of reality invariably suffers a conspicuous impoverishment, which is enormous in the less lavishly endowed; it is here reduced to a mere schema, limited to the inferior concepts.