Conceptions of Classes.—But a large part of our conceptions, if we carefully observe the operations of our own minds, are not particular, but general, not of individual objects, but of classes of objects. Of this, any one may satisfy himself on a little reflection. How are these conceptions formed?
Such Conceptions, how formed.—The process of forming a general conception, I take to be this: The several elements that compose our conception of an individual object, being originally presented, as we have already said, one by one, in the discrete, and not in the concrete, it is of course in our power to conceive of any one of these elements by itself. No new power or faculty is needed for this. By the usual laws of suggestion any one of these elements may be presented to the mind, distinct from those with which, in perception, it is associated, and as such it may be the object of attention and thought. I may thus conceive of the color, the form, the size, or the fragrance of a flower.
Extension of the Process to other Objects.—It is of the form, color, etc., of some particular flower, as yet, however, and not of form and color in general, that I conceive. Suppose, now, that other flowers are presented to my notice, possessing the same form and color, for example, red. Presently I observe other objects, besides flowers, that are of the same color—horses, cows, tables, books, cloths. As the field of observation enlarges, still other objects are added to the list, until that which I first conceived of as the peculiar property of a single flower, the rose, and of a single specimen, no longer is appropriated in my thoughts to any individual object or class of objects, but becomes a general conception. It is an abstraction and also a generalization; an abstraction because it no longer denotes or connotes any individual object, but stands before the mind as simple, pure quality, red, or redness; a generalization inasmuch as it is a quality pertaining equally to a great variety of objects.
The Process carried still further.—Having thus obtained the general conception of red, and, in like manner, of blue, violet, yellow, indigo, orange, etc., etc., I may carry the process still further, and form a conception more general than either, and which shall include all these. These are all varieties denoting the certain peculiarity of appearance which external objects present to the eye. Fixing my thought upon this, their common characteristic, I no longer conceive of red, or blue, or violet, as such, but of color in general.
In like manner, I observe the properties of different triangles—right-angled, obtuse-angled, acute-angled, equilateral, isosceles. I leave out of view whatever is peculiar to each of these varieties, retaining only what is common to them all—the property of three-sidedness; and my conception is now a general one—triangle.
It is in this manner that we form the conceptions expressed by such terms as animal, man, virtue, form, beauty, and the like. A large proportion of the words in ordinary use, are of this sort. They are the names or expressions of abstract, general, conceptions: abstract, in that they do not relate to any individual object; general, in that they comprehend, and are equally applicable to a great variety of objects.
Process of Classification.—The process of classification is essentially the same with that by which we form general abstract conceptions. Observing different objects, I find that they resemble each other in certain respects, while in others they differ. Objects A, B, and C, differ, for instance, in form, and size, and weight, and fragrance, but agree in some other respect, as in color. On the ground of this resemblance, I class them together in my conceptions. In so doing, I leave out of view all other peculiarities, the points in which they differ, and take into account only the one circumstance in which they agree. In the very act of forming a class, I have formed a general conception, which lies at the basis of that classification.
Tendency of the Mind.—The tendency of the mind to group individual objects together on the ground of perceived resemblances, is very strong, and must be regarded as one of the universal and instinctive propensities of our nature, one of the laws of mental action. As we have already remarked, respecting general abstract terms, a large portion of the language of ordinary life is the language of classification. The words which constitute by far the greater part of the names of things, are common nouns, that is, names of classes. The names of individual objects are comparatively few. Adjectives, specifying the qualities of objects, denote groups or classes possessing that common quality. Adverbs qualifying verbs or adjectives, designate varieties or classes of action and of quality. Indeed, the very existence of language as a medium of communication, and means of expression, involves and depends upon this tendency of the mind to class together, and then to designate by a common noun, objects diverse in reality, but agreeing in some prominent points of resemblance. In no other way would language be possible to man, since, to designate each individual object by a name peculiar to itself, would be an undertaking altogether impracticable.
Rudeness of the earlier Attempts.—The first efforts of the mind at the process of classification are, doubtless, rude and imperfect. The infancy of the individual, and the infancy of nations and races, are, in this respect, alike; objects are grouped roughly and in the mass, specific differences are overlooked, and individuals differing widely and essentially are thrown into the same class, on the ground of some observed and striking resemblance. As observation becomes more minute, and the mind advances in culture and power of discrimination, these ruder generalizations are either abandoned or subdivided into genera and species, and the process assumes a scientific form. What was at first mere classification, becomes now, in the strictest sense, generalization.