Books, like conversation, rarely give us any precise ideas: nothing is so common as to read and converse unprofitably. We must here repeat what Locke has so strongly urged—Define your terms.

Cf. Locke: "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." | An Essay Concerning Human Understanding (1689) Book III, chapter 4