But though the invention of nouns adjective be much more natural than that of the abstract nouns substantive derived from them, it would still, however, require a considerable degree of abstraction and generalization. Those, for example, who first invented the words, _green_, _blue_, _red_, and the other names of colours, must have observed and compared together a great number of objects, must have remarked their resemblances and dissimilitudes in respect of the quality of colour, and must have arranged them, in their own minds, into different classes and assortments, according to those resemblances and dissimilitudes. An adjective is by nature a general, and in some measure, an abstract word, and necessarily presupposes the idea of a certain species or assortment of things, to all of which it is equally applicable. The word _green_ could not, as we were supposing might be the case of the word _cave_, have been originally the name of an individual, and afterwards have become, by what grammarians call an Antonomasia the name of a species. The word _green_ denoting, not the name of a substance, but the peculiar quality of a substance, must from the very first have been a general word, and considered as equally applicable to any other substance possessed of the same quality. The man who first distinguished a particular object by the epithet of _green_, must have observed other objects that were not _green_, from which he meant to separate it by this appellation. The institution of this name, therefore, supposes comparison. It likewise supposes some degree of abstraction. The person who first invented this appellation must have distinguished the quality from the object to which it belonged, and must have conceived the object as capable of subsisting without the quality. The invention, therefore, even of the simplest nouns adjective, must have required more metaphysics than we are apt to be aware of. The different mental operations, of arrangement or classing, of comparison, and of abstraction, must all have been employed, before even the names of the different colours, the least metaphysical of all nouns adjective, could be instituted. From all which I infer, that when languages were beginning to be formed, nouns adjective would by no means be the words of the earliest invention.