The tenacity with which many thinkers still cling to a belief in the reality and absoluteness of such distinctions as those expressed by the terms "organic and inorganic", "living and dead", "animal and vegetable", "rational and instinctive", etc., is plainly the result of this tendency to attribute to Nature the exactness of words.
The terms animal and plant were not established as the result of scientific and thorough study and comparison, but were first introduced to give expression to the most superficial and obvious difference between living things.
Originally an animal was a living thing which could move and feel, and a plant one which could not; and this is still the popular view, although the scientific definitions are quite different. As soon as primitive man began to observe and to generalize and to use abstract words, one of the first generalizations which attracted his attention was that, of the bodies which were of most importance to him, and like him grew up, matured, and died, some were still more like himself in having the power to move and feel, while others lacked this power, and were fixed and insensible. We do not intend to imply that this generalization took this definite shape, but simply that it was reached and put into words at a very early period; and this is shown by the fact that in nearly all languages, and among all but the lowest races of men, this division of living things into two great groups is recognized, and definite words are employed to distinguish the animal from the vegetable organism. At a later period, when living things came to be more carefully studied, and superficial observation gave place to more exact and careful comparison, these two groups were found to have a real existence in Nature; and, as long as this study was confined to the more familiar, abundant, and easily-studied organisms, the increase of scientific knowledge only served to render the distinctness of the two groups more evident. It was soon found that all the common plants are alike in many other respects besides being fixed and insensible, and that all ordinary animals have many common characteristics, and it was found convenient to express these resemblances briefly and absolutely in definitions, and thus the terms animal and plant came to have a more and more exact and scientific value. It was seen, too, that all living things have much in common, and that the chief difference between plants and animals is the possession by the latter of the new properties of sensation and voluntary motion, added to those characteristics which they share with the plants. It is not at all strange that it was thought desirable to express this fact by a word, and that, in the same way that living things were said to differ from inorganic bodies by having, in addition to all the properties of the latter, a new and higher quality, vitality, animals were said to possess the new and higher faculties of feeling and will, in addition to all the faculties of the plant.
Thus was gradually built up that conception of Nature which re-