To conclude. This is that which in short I would say, viz. that all the great business of GENERA and SPECIES, and their ESSENCES, amounts to no more but this:--That men making abstract ideas, and settling them in their minds with names annexed to them, do thereby enable themselves to consider things, and discourse of them, as it were in bundles, for the easier and readier improvement and communication of their knowledge, which would advance but slowly were their words and thoughts confined only to particulars. CHAPTER IV. OF THE NAMES OF SIMPLE IDEAS. 1. Names of simple Ideas, Modes, and Substances, have each something peculiar. Though all words, as I have shown, signify nothing immediately but the ideas in the mind of the speaker; yet, upon a nearer survey, we shall find the names of SIMPLE IDEAS, MIXED MODES (under which I comprise RELATIONS too), and NATURAL SUBSTANCES, have each of them something peculiar and different from the other. For example:-- 2. First, Names of simple Ideas, and of Substances intimate real Existence. First, the names of SIMPLE IDEAS and SUBSTANCES, with the abstract ideas in the mind which they immediately signify, intimate also some real existence, from which was derived their original pattern. But the names of MIXED MODES terminate in the idea that is in the mind, and lead not the thoughts any further; as we shall see more at large in the following chapter. 3. Secondly, Names of simple Ideas and Modes signify always both real and nominal Essences. Secondly, The names of simple ideas and modes signify always the real as well as nominal essence of their species. But the names of natural substances signify rarely, if ever, anything but barely the nominal essences of those species; as we shall show in the chapter that treats of the names of substances in particular. 4. Thirdly, Names of simple Ideas are undefinable. Thirdly, The names of simple ideas are not capable of any definition; the names of all complex ideas are. It has not, that I know, been yet observed by anybody what words are, and what are not, capable of being defined; the want whereof is (as I am apt to think) not seldom the occasion of great wrangling and obscurity in men's discourses, whilst some demand definitions of terms that cannot be defined; and others think they ought not to rest satisfied in an explication made by a more general word, and its restriction, (or to speak in terms of art, by a genus and difference,) when, even after such definition, made according to rule, those who hear it have often no more a clear conception of the meaning of the word than they had before. This at least I think, that the showing what words are, and what are not, capable of definitions, and wherein consists a good definition, is not wholly besides our present purpose; and perhaps will afford so much light to the nature of these signs and our ideas, as to deserve a more particular consideration.