Let me illustrate my meaning by at least one instance.
Among the words which have proved spider's webs, ensnaring even the greatest intellects of the world from Aristotle down to Leibniz, the terms genus, species, and individual occupy a very prominent place. The opposition of Aristotle to Plato, of the Nominalists to the Realists, of Leibniz to Locke, of Herbart to Hegel, turns on the true meaning of these words. At school, of course, all we can do is to teach the received meaning of genus and species; and if a boy can trace these terms back to Aristotle's γένος and εἶδος, and show in what sense that philosopher used them, every examiner would be satisfied.
But the time comes when we have to act as our own examiners, and when we have to give an account to ourselves of such words as genus and species. Some people write, indeed, as if they had seen a species and a genus walking about in broad daylight; but a little consideration will show us that these words express subjective concepts, and that, if the whole world were silent, there would never have been a thought of a genus or a species. There are languages in which we look in vain for corresponding words; and if we had been born in such a language, these terms and thoughts would not exist for us. They came to us, directly or indirectly, from Aristotle. But Aristotle did not invent them, he only defined them in his own way, so that, for instance, according to him, all living beings would constitute a genus, men a species, and Socrates an individual.
No one would say that Aristotle had not a perfect right to define these terms, if those who use them in his sense would only always remember that they are thinking the thoughts of Aristotle, and not their own. The true way to shake off the fetters of old words, and to learn to think our own thoughts, is to follow them up from century to century, to watch their development, and in the end to bring ourselves face to face with those who first found and framed both words and thoughts. If we do this with genus and species, we shall find that the words which Aristotle defined—viz., γένος and εἶδος—had originally a very different and far more useful application than that which he gave to them. Γένος, genus, meant generation, and comprehended such living beings only as were known to have a common origin, however they might differ in outward appearance, as, for instance, the spaniel and the bloodhound, or, according to Darwin, the ape and the man. Εἶδος or species, on the contrary, meant appearance, and comprehended all such things as had the same form or appearance, whether they had a common origin or not, as if we were to speak of a species of four-footed, two-footed, horned, winged, or blue animals.
That two such concepts, as we have here explained, had a natural justification we may best learn from the fact that exactly the same thoughts found expression in Sanskrit. There, too, we find gâti, generation, used in the sense of genus, and opposed to âkriti, appearance, used in the sense of species.
So long as these two words or thoughts were used independently (much as we now speak of a genealogical as independent of a morphological classification) no harm could accrue. A family, for instance, might be called a γένος, the gens or clan was a γένος, the nation (gnatio) was a γένος, the whole human kith and kin was a γένος; in fact, all that was descended from common ancestors was a true γένος. There is no obscurity of thought in this.
On the other side, taking εἶδος or species in its original sense, one man might be said to be like another in his εἶδος or appearance. An ape, too, might quite truly be said to have the same εἶδος or species or appearance as a man, without any prejudice as to their common origin. People might also speak of different εἴδη or forms or classes of things, such as different kinds of metals, or tools, or armour, without committing themselves in the least to any opinion as to their common descent.
Often it would happen that things belonging to the same γένος, such as the white man and the negro, differed in their εἶδος or appearance; often also that things belonging to the same εἶδος, such as eatables, differed in their γένος, as, for instance, meat and vegetables.
All this is clear and simple. The confusion began when these two terms, instead of being co-ordinate, were subordinated to each other by the philosophers of Greece, so that what from one point of view was called a genus, might from another be called a species, and vice versâ. Human beings, for instance, were now called a species, all living beings a genus, which may be true in logic, but is utterly false in what is older than logic—viz., language, thought, or fact. According to language, according to reason, and according to Nature, all human beings constitute a γένος, or generation, so long as they are supposed to have common ancestors; but with regard to all living beings we can only say that they form an εἶδος—that is, agree in certain appearances, until it has been proved that even Mr. Darwin was too modest in admitting at least four or five different ancestors for the whole animal world.[16]
In tracing the history of these two words, γένος and εἶδος, you may see passing before your eyes almost the whole panorama of philosophy, from Plato's ideas down to Hegel's Idee. The question of genera, their origin and subdivision, occupied chiefly the attention of natural philosophers, who, after long controversies about the origin and classification of genera and species, seem at last, thanks to the clear sight of Darwin, to have arrived at the old truth which was prefigured in language—namely, that Nature knows nothing but genera, or generations, to be traced back to a limited number of ancestors, and that the so-called species are only genera, whose genealogical descent is as yet more or less obscure.