The first of these rules is not always adhered to; and, in the progress of a science, as subtler and more abstract relations are discovered amongst the facts, the meaning of a term may have to be modified and shifted further and further from its popular use.  The term ‘rent,’ for example, is used by economists, in such a sense that they have to begin the discussion of the facts it denotes, by explaining that it does not imply any actual payment by one man to another.  Here, for most readers, the meaning they are accustomed to, seems already to have entirely disappeared.  Difficulties may, however, be largely overcome by qualifying the term in its various relations, as produce-rents, ground-rents, customary rents, and so forth, (Cf.  Dr. Keynes’ Scope and Method of Political Economy, chap. 5.)

Sec. 6.  Definitions affect the cogency of arguments in many ways, whether we use popular or scientific language.  If the definitions of our terms are vague, or are badly abstracted from the facts denoted, all arguments involving these terms are inconclusive.  There can be no confidence in reasoning with such terms; since, if vague, there is nothing to protect us from ambiguity; or, if their meaning has been badly abstracted, we may be led into absurdity—­as if ‘impudence’ should be defined in such a way as to confound it with honesty.

Again, it is by definitions that we can best distinguish between Verbal and Real Propositions.  Whether a term predicated is implied in the definition of the subject, or adds something to its meaning, deserves our constant attention.  We often persuade ourselves that statements are profound and important, when, in fact, they are mere verbal propositions.  “It is just to give every man his due”; “the greater good ought to be preferred to the less”; such dicta sound well—­indeed, too well!  For ‘a man’s due’ means nothing else than what it is just to give him; and ‘the greater good’ may mean the one that ought to be preferred:  these, therefore, are Truisms.  The investigation of a definition may be a very valuable service to thought; but, once found, there is no merit in repeating it.  To put forward verbal or analytic propositions, or truisms, as information (except, of course, in explaining terms to the uninstructed), shows that we are not thinking what we say; for else we must become aware of our own emptiness.  Every step forward in knowledge is expressed in a real or synthetic proposition; and it is only by means of such propositions that information can be given (except as to the meaning of words) or that an argument or train of reasoning can make any progress.