If, then, we consider the foregoing figure merely as a means of representing the gradation to the eye, the image in moving, by hypothesis, from the moment of perception, _P_, is less and less in contact with reality, becomes simplified, impoverished, and loses some of its constitutive elements. At _X_ it crosses the middle threshold to approach nearer and nearer to the concept. At _G_ let us locate generic images, primitive forms of generalization, whose nature and process of becoming are well-known;[134] we should place farther along, at _S_, schematic images, which require a higher function of mind. Indeed, the generic image results from a spontaneous fusion of like or very analogous images--such as the vague representation of the oak, the horse, the negro, etc.; it belongs to only one class of objects. The schematic image results from a voluntary act; it is not limited to exact resemblances--it rises into abstraction; so it is scarcely accompanied by a fleeting representation of concrete objects--it is almost reduced to the word. At a higher level, it is freed from all sensuous elements or pictures, and is reduced, in the present instance, to the mere notion of value--it is not different from a pure concept. While the artist and the mechanic build with concrete images, the commercial imagination can act directly neither on things nor on their immediate representations, because from the time that it goes beyond the primitive age it requires a substitution of increasing generality; materials become values that are in turn reducible to symbols. Consequently, it proceeds as in the stating and solving of abstract problems in which, after having substituted for things and their relations figures and letters, calculation works with signs, and indirectly with things. Aside from the first moment of invention, the finding of the idea--an invariable psychological state--it must be recognized that in its development and detailed construction the commercial imagination is made up chiefly of calculations and combinations that hardly permit concrete images. If we admit, then,--and this is unquestionable--that these are the materials _par excellence_ of the creative imagination, we shall be disposed to hold that the imaginative type we are now studying is a kind of involution, a case of impoverishment--an unacceptable thesis as regards the invention itself, but strictly acceptable as regards the conditions that necessity imposes upon it.