The idea of each color had originally entire concreteness given to it by an object possessing the color; as some of the unmodified names, such as orange and violet, show us. The dissociation of each color from the object specially associated with it in thought at the outset, went on as fast as the color came to be associated in thought with objects unlike the first, and unlike one another. The idea of orange was conceived in the abstract more fully in proportion as the various orange-colored objects remembered, cancelled one another's diverse attributes, and left outstanding their common attribute. So is it if we ascend a stage and note how there arises the abstract idea of color apart from particular colors. Were all things red the conception of color in the abstract could not exist. Imagine that every object was either red or green, and it is manifest that the mental habit would be to think of one or other of these two colors in connection with anything named. But multiply the colors so that thought rambles undecidedly among the ideas of them that occur along with any object named, and there results the notion of indeterminate color--the common property which objects possess of affecting us by light from their surfaces, as well as by their forms. For evidently the notion of this common property is that which remains constant while imagination is picturing every possible variety of color. It is the uniform trait in all colored things; that is--color in the abstract. Words referring to quantity furnish cases of more marked dissociation of abstract from concrete. Grouping various things as small in comparison either with those of their kind or with those of other kinds, and similarly grouping some objects as comparatively great, we get the opposite abstract notions of smallness and greatness. Applied as these are to innumerable very diverse things--not objects only, but forces, times, numbers, values--they have become so little connected with concretes, that their abstract meanings are very vague. Further, we must note that an abstract idea thus formed often acquires an illusive independence; as we may perceive in the case of motion, which, dissociated in thought from all particular bodies and velocities and directions, is sometimes referred to as though it could be conceived apart from something moving. Now all this holds of the subjective as well as of the objective; and among other states of consciousness, holds of the emotions as known by introspection. By the grouping of those re-representative feelings above described, which, differing among themselves in other respects, have a component in common, and by the consequent mutual cancelling of their diverse components, this common component is made relatively appreciable, and becomes an abstract feeling. Thus is produced the sentiment of moral obligation or duty. Let us observe its genesis.