28. Thirdly, when the same sign is not put for the same idea.
Thirdly, He that puts not constantly the same sign for the same idea, but uses the same word sometimes in one and sometimes in another signification, ought to pass in the schools and conversation for as fair a man, as he does in the market and exchange, who sells several things under the same name.
29. Fourthly, when words are diverted from their common use.
Fourthly, He that applies the words of any language to ideas different from those to which the common use of that country applies them, however his own understanding may be filled with truth and light, will not by such words be able to convey much of it to others, without defining his terms. For however the sounds are such as are familiarly known, and easily enter the ears of those who are accustomed to them; yet standing for other ideas than those they usually are annexed to, and are wont to excite in the mind of the hearers, they cannot make known the thoughts of him who thus uses them.
30. Fifthly, when they are names of fantastical imaginations.
Fifthly, He that imagined to himself substances such as never have been, and filled his head with ideas which have not any correspondence with the real nature of things, to which yet he gives settled and defined names, may fill his discourse, and perhaps another man's head, with the fantastical imaginations of his own brain, but will be very far from advancing thereby one jot in real and true knowledge.
31. Summary.
He that hath names without ideas, wants meaning in his words, and speaks only empty sounds. He that hath complex ideas without names for them, wants liberty and dispatch in his expressions, and is necessitated to use periphrases. He that uses his words loosely and unsteadily will either be not minded or not understood. He that applies his names to ideas different from their common use, wants propriety in his language, and speaks gibberish. And he that hath the ideas of substances disagreeing with the real existence of things, so far wants the materials of true knowledge in his understanding, and hath instead thereof chimeras.
32. How men's words fail when they stand for Substances.
In our notions concerning Substances, we are liable to all the former inconveniences: v. g. he that uses the word TARANTULA, without having any imagination or idea of what it stands for, pronounces a good word; but so long means nothing at all by it. 2. He that, in a newly-discovered country, shall see several sorts of animals and vegetables, unknown to him before, may have as true ideas of them, as of a horse or a stag; but can speak of them only by a description, till he shall either take the names the natives call them by, or give them names himself. 3. He that uses the word BODY sometimes for pure extension, and sometimes for extension and solidity together, will talk very fallaciously. 4. He that gives the name HORSE to that idea which common usage calls MULE, talks improperly, and will not be understood. 5. He that thinks the name CENTAUR stands for some real being, imposes on himself, and mistakes words for things.