Scientific Classification.—Classification, however scientific, is still essentially the process already described. We observe a number of individuals, for example, of our own species. Certain resemblances and differences strike us. Some have straight hair, and copper complexion, others, woolly hair, and black complexion, others, again, differ from the preceding in both these respects. Neglecting minor and specific differences, we fix our attention on the grand points of resemblance, and thus form a general conception, which embraces whatever characteristics belong, in common, to the several individuals which thus resemble each other. To this general conception we appropriate the name Indian, Negro, Caucasian, etc., which henceforth represent to us so many classes or varieties of the human race. Bringing these classes again into comparison with each other, we observe certain points of resemblance between them, and form a conception still more general, that of man.
Further Illustration of the same Process.—In this way the genera and species of science are formed. On grounds of observed resemblance, we class together, for example, certain animals. They differ from each other in color, size, and many other respects, but agree in certain characteristics which we find invariable, as, for example, the form of the skeleton, number of vertebræ, number and form of teeth, arrangement of organs of digestion. We give a name to the class thus formed—carnivora, rodentia, etc. The class thus formed and named, we term the genus, while the minor differences mark the subordinate varieties or species included under the genus. In the same way, comparing other animals, we form other genera. Bringing the several genera also into comparison, we find them likewise agreeing in certain broad resemblances. These points of agreement, in turn, constitute the elements of a conception and classification still wider and more comprehensive than the former. Under this new conception I unite the previous genera, and term them all mammalia. And so on to the highest and widest generalizations of science.
Having formed our classification we refer any new specimen to some one of the classes already formed, and the more complete our original survey, the more correct is this process of individual arrangement. It is remarked by Mr. Stewart, that the islanders of the Pacific, who had never seen any species of quadruped, except the hog and the goat, naturally inferred, when they saw a cow, that she must belong to one or the other of these classes. The limitations of human knowledge may lead the wisest philosopher into essentially the same error.
It is in the way now described that we form genera, and species, and the various classes into which, for purposes of science, we divide the multitude of objects which are presented in nature, and which, but for this faculty, would appear to us but a confused and chaotic assemblage without number, order, or arrangement. The individuals exist in nature—not the classes, and orders, and species: these are the creations of the human mind, conceptions of the brain, results of that process of thought now described as the reflective faculty in its synthetic form.
Importance of this Process.—It is evident at a glance that this process lies at the foundation of all science. Had we no power of generalization—had we no power of separating, in our thoughts, the quality from the substance to which it pertains, of going beyond the concrete to the abstract, beyond the particular to the general—could we deal only with individual existences, neither comparison nor classification would be possible; each particular individual object would be a study to us by itself, nor would any amount of diligence ever carry us beyond the very alphabet of knowledge.
Existence of general Conceptions questioned.—Important as this faculty may seem when thus regarded, it has been questioned by some whether, after all, we have, in fact, or can have, any general abstract ideas; whether triangle, man, animal, etc., suggest in reality any thing more to the mind than simply some particular man, or triangle, or animal, which we take to represent the whole class to which the individual belongs.
There can be no question, however, that we do distinguish in our minds the thought of some particular man, as Mr. A, or some particular sort of man, as black man, white man, from the thought suggested by the term man; and the thought of an isosceles or right-angled triangle, from the thought suggested by the unqualified term triangle. They do not mean the same thing; they have not the same value to our minds. Now there are a great multitude of such general terms in every language, they have a definite meaning and value, and we know what they mean. It must be then that we have general abstract ideas, or general conceptions.
Argument of the Nominalist.—But the nominalist replies. The term man, or triangle, awakens in your mind, in reality and directly, only the idea of some particular individual or triangle, and this stands as a sort of type or representation of other like individuals of whom you do not definitely think as such and so many. I reply, this cannot be shown; but even if it were so, the very language of the objection implies the power of having general conceptions. If the individual man or triangle thought of stands as a type or representation, as it is said, of a great number of similar men and triangles, then is there not already in my mind, prior to this act of representation, the idea of a class of objects, arranged according to the law of resemblance, in other words, a general abstract idea or conception? If I had not already formed such an idea, the particular object presented to my thoughts could not stand as type or representation of any such thing, or of any thing beyond itself, for the simple reason that there would be nothing of the sort to represent.
Further Reply.—Besides, there is a large class of general terms to which this reasoning of the nominalist would not at all apply—such terms as virtue, vice, knowledge, wisdom, truth, time, space—which manifestly do not awaken in the mind the thought of any particular virtue or vice, any particular truth, any definite time, any definite space, but a general notion under which all particular instances may be included. To this the nominalist will perhaps reply, that in such cases we are really thinking, after all, of mere names or signs, as when we use the algebraic formula x-y, a mere term of convenience, having indeed some value, we do not know precisely what, itself the terminus and object of our thought for the time being. In such cases the mind stops, he would say, with the term itself, and does not go beyond it to conjure up a general conception for it. So it is with the terms virtue, vice; so with the general terms, class, species, genus, man, animal, triangle; they are mere collective terms, signs, formulas of convenience, to which you attach no more meaning than to the expression x-y. If you would find their meaning and attach any definite idea to them, you must resolve them into the particular objects, the particular vices, virtues, etc., which go to make up the class.
I reply to all this, you are still classifying, still forming a general conception, the expression of which is your so called formula, x-y, alias virtue, man, and the like.